The following is a summary of most of the talks associated with the Bioastronomy 2004: Habitable Worlds conference. This conference continues a succession of meetings organized by the IAU Commission 51 (Bioastronomy). The objective is to review progress in all fields of bioastronomy (also known as astrobiology). (Interested readers may also want to consult my summary of Bioastronomy 2002: Life Among the Stars.)
A caveat is in order. I am not an expert in many of these fields. I have recorded what I understood the speaker's main points to be. In some places I have added interpretation or questions. However, any errors in this document almost certainly reflect my lack of understanding of a field and caution should be used in order that a speaker's remarks are not overinterpreted based on what I recorded. In addition to differing levels of understanding, the talks were of differing length. Thus, the length of my notes from speaker to speaker reflects many factors. Finally, I (rightly or wrongly) took no notes on the posters. Thus, there are a number of presentations not recorded here.
Also, I have used a fair amount of jargon or specific terms at various points in this summary. Given time constraints I may be willing and able to explain what various terms mean if asked. Here is a bit of a glossary for some shorthand I've used:
extrasolar planet
civilization
intelligence
habitable zone
brown dwarf
kiloyears = 1000 yrs; megayears = 1 million years; gigayears = 1 billion years
Anything surrounded by braces is either a place where my notes are unclear, I am adding some additional material, or voicing an opinion.
These represent comments made during the discussion period after each paper.
Addressed the question of what makes a planet "habitable"? He suggested that for a planet to be habitable there are both local aspects (e.g., presence of water, presence of oxygen, geology, etc.) and external aspects (e.g., properties of host star, dynamic stability of planetary system, etc.). Acknowledging his bias as an astronomer, he argued that a true assessment of a planet's habitability must include both. Thus, an ecosystem is defined not only by a planet's surface [and interior?] but also by the planet's place around its star.
He then summarized various planet searches to date and their successes.
He suggested a definition for habitable planets that included the following possibilities, then discussed each in order.
solar system-like;
terrestrial planets around low mass stars and BDs;
moons of giant planets; and
giant planets themselves.
A solar system analog is one in which there are terrestrial planets in the inner part of the system and a giant planet around 5 AU. He mentioned the possibility that giant planets are required to help clean the system of debris (comets, asteroids) that might otherwise impact the inner planets too often. He showed an image of the epsilon Eridani system, in which this process may have been detected, as there is a circumstellar debris disk, but it has a hole in it, possibly cleared by a planet. He suggested that epsilon Eridani might be how the Sun and Kuiper Belt would look from a distance.
One can assess the dynamical stability of the known extrasolar planet systems. Of the roughly 120 known extrasolar planets, only 4 are close to being solar system analogs in the sense of having a giant planet at a few AU. Of these, only one looks really promising:
The giant planets in both systems have high eccentricities, so they would probably render any terrestrial planet dynamically unstable.
The system has a giant planet at the correct distance, but also giant planets within a few AU of the star, so it is unlikely to have terrestrial planets.
Naively, then one might suggest that roughly 1% of planetary systems would contain habitable planets [or more precisely, terrestrial planets that might be habitable]. However, there is still a significant selection bias against finding long-period Jovian planets, so this 1% value is almost certainly a lower limit.
He then summarized a number of long-term [astrometric?] programs (including one that started in the 1980s). Of 15 stars studied, effectively none found with definite Jovian planets, but 5 candidates. Another program had 23 stars, of which 3 have Jovian planets, 14 showed nothing, and another 6 were candidates. Taken together, these programs suggested 25% of solar type stars might have Jovian planets on the correct orbits to allow for habitable planets.
Finally, mentioned attempts to assess the dynamical stability of systems (Barrie et al; Jones et al.). They looked at 9 of the known exoplanetary systems, of which 4 resulted in non-stable orbits for terrestrial planets. Extrapolating, one would expect 30% of stars could have terrestrial planets on stable orbits in the stars' HZs.
One of the difficulties in finding terrestrial-mass planets around main-sequence stars is that terrestrial-mass planets are so much less massive. The mass ratio is much more favorable for low-mass stars and BDs. He described a program using the UVESS instrument on the VLT to search around low-mass stars and BDs. He suggested that they may have found a 91 Earth-mass planet in a 91-day orbit, but it still needs to be confirmed, and he didn't say which star.
IR spectrographs should be able to detect a Neptune-mass planet around BDs. Of course, BDs have no interior fusion source and are cooling, so their HZs become steadily smaller and closer to the BD.
of the known exoplanets, about 35% have semi-major axes around 0.6 to 1.5 AU, within their stars' HZs. A satellite around one of these giant exoplanets might be habitable. Detecting such a satellite requires only 1--10 m/s doppler velocity precision but it is required on the exoplanet itself, not the star. This is challenging, and he was fairly pessimistic. More likely would be that one could detect the transit of a satellite of one of these planets. It requires roughly photometric accuracy to 1 part in 100,000, but the Kepler mission should be able to do this. He noted that Kepler should find roughly 7 transiting giant planets for every 100,000 stars observed.
Although running out of time, he flashed the Sagan & Salpeter paper that discusses the possibility of life in the atmospheres of gas giant planets.
Q: Pointed out that the HZ around an M-type star might be quite complicated [due to tidal lock, flares, etc.]
Q: Detecting Jupiter around the Sun might actually be quite difficult. Jupiter's orbital period is about 12 years. The Sun displays an activity cycle (linked to sunspots) of 11 years. A distant observer might conclude, quite reasonably, that the effects seen in any spectra result from the Sun's activity and not from a planet!
He discussed the PSR B1620-26 system. He pointed out that pulsar timing allows for much higher precision, and he reminded the audience that the first exoplanet system found is around a pulsar.
He focussed on globular clusters. These are dense clusters of stars, containing many white dwarfs and neutron stars/pulsars. Dynamical exchange is possible so that, e.g., in interactions between a pulsar and a star-planet binary, the pulsar might end up with a planetary companion. Moreover, globular clusters are old so they can place constraints on the extent to which stellar metallicity is important for forming planets. He has been focussing on the globular cluster M4, which contains the millisecond pulsar PSR B1620-26.
Soon after the discovery of this pulsar, it was clear that it was at least a binary system and probably a trinary. Current thinking is that there was a dynamical exchange between a pulsar-white dwarf binary and main sequence star-planetary system. The main sequence star (with its planetary system) could have spent most of its time near the outskirts of the cluster, which would have allowed a planet in a 5 AU orbit to survive. After the dynamical exchange, the result was a pulsar-main sequence star binary, orbited by the planet. The main sequence star then formed a white dwarf, spinning up the pulsar.
The white dwarf is now constrained to have a mass of 0.34 solar masses, meaning that the planetary mass is probably 1.7 Jovian masses. Given the age of M4, this planet is old, probably about 12.7 Gyr.
Conclusion: Either giant planets form by a gravitational instability collapse method [in which part of the planetary disk simply becomes unstable and collapses to form a planet] or planets are incredibly easy to form.
Also made comment that the low metallicity of M4 places constraints on the ease of planet migration in the sense that higher metallicity = more efficient migration.
Interesting paper on the possibility of finding planets around white dwarfs. In particular, there is a class of white dwarfs known as DAZs that have enhanced metallicites [and/or hydrogen] in their atmospheres. However, the time it would take for these elements to settle out of the white dwarf atmosphere is quite short, meaning that there must be a fairly steady source of material to the white dwarf. One possibility is that the white dwarf accretes from the general interstellar medium. However, he has found a couple for which that doesn't seem to work and suggests that planets in orbit about the white dwarf may be another source of material.
He described a program to search for water masers from the atmospheres of exoplanets. [It is not obvious to me that such would be detectable. Giant planet atmospheres are quite turbulent, but a maser requires a long path length of material at nearly the same velocity.]
He began by describing a habitable planet as one that had at least liquid water on its surface over geological time scales.
He referred to the carbon-sulfur cycle and its feedback effect. Namely, CO2 is absorped into oceans, which takes CO2 out of the atmosphere, but volcanoes put CO2 back into the atmosphere. Sulfer may be important in plate tectonics, so that the CO2 can be recycled. The feedback effect is that, if the oceans take out too much CO2, the atmosphere cools but doesn't affect volcanos, which continue to pump CO2 into the atmosphere, rewarming the planet. If volcanoes pump too much CO2 into the atmosphere, the oceans warm, which increases their CO2 uptake, thereby cooling the planet.
He then summarized planet formation and discussed each of the items in turn:
Protoplanetary disk: A protoplanetary disk forms with or around a young star. Observations (Haisch et al. 2001) suggest 50% of young stars have protoplanetary disks, but these seem to dissipate within about 6 Myr (suggesting that planet formation must get started in this duration).
Dust grains accrete to form km-sized planetismals: A km-sized object is important because at this size, gravitational effects become important. However, it is not known how to form such objects. Do they form via turbulent concentration? In this method, there would be turbulent eddies in the protoplanetary disk [much like in a stream], which would concentrate the dust grains. However, attempts to model this process in detail have been unsuccessful. Do they form via gravitational instability? The lack of understanding here could be an important stumbling block. Could metallicity be important?
Primitive meteorites contain components that are about 1 mm in size. There is a very narrow range of sizes for these components. Not clear what this means. It is known from measurements of radioactive isotopes like Aluminum-26 that these 1-mm sized components were incorporated into the parent bodies very quickly, within 2--3 Myr.
Could there be special conditions required? OTOH, 60% of stars younger than 400 Myr have debris disks, which contain no gas so are thought to be "second generation," namely resulting from the collision/destruction of comets or asteroids.
Planets: Forming planets from planetismals is easy, typically happens via runaway growth [aided by gravitational focussing] in which the km-sized objects start attracting smaller objects and each other together. Simulations suggest that lunar- to Mars-sized objects can build up within 0.1--1 Myr.
However, not clear that all terrestrial-mass planets are habitable. E.g., small planets can lose their atmospheres quickly. Small planets also cool quickly, which could mean that their internal heat source to drive a magnetic field and plate tectonics disappears.
He described work to assess the habitability of planets in the upsilon Andromedae system. Also pointed out that we may have lost a planet in our own solar system, namely, the Asteroid Belt is the remnant of a planet that failed to form because of the gravitational influence of Jupiter.
Giant planets can be bad for the health of terrestrial planets. They can migrate inward, which would tend to scatter terrestrial planets out of the system [assuming that they had even formed]. It is not clear that if a giant planet migrates all the way into its star that any terrestrial planets will form in the aftermath. Might be too little material left in the disk. Also, giant planets might delay the runaway growth that allows terrestrial planets to form or scatter planetismals out of the disk [as is thought to have happened in the Asteroid Belt].
Giant planets may have been important for the Earth's oceans. Earth's oceans represent 0.02% of the planet's mass. Some water almost certainly lost in early giant impacts and some in oxidizing water in the mantle. Moreover, the early solar nebula was hot, so it would have been tough for water to condense on Earth. He showed a graph illustrating that water content increases with distance from Sun. However, getting asteroids to hit the Earth is tough, because the Earth is so small. He quoted a probability of 1E-6. Giant planets can kick asteroids into the inner solar system, increasing the probability that they will hit Earth.
Carbonacous asteroids are 5--10% water and are chemically similar. They could have supplied lots of water to the Earth. Comets are problematic, because their deuterium/hydrogen ratio (and Ar/H2O ratio) is different than Earth.
Described simulations to assess how the properties of the giant planets affect the water delivery to Earth. For instance, making Jupiter or Saturn less massive or farther away reduces their impact on the Asteroid Belt and reduces the water delivery to the Earth. Making eccentricity larger or mass larger [or ...] can also drop dramatically the amount of water delivered, e.g., to only 0.01% of Earth mass.
In the future
Spitzer will provide more information on protoplanetary disks;
Doppler surveys will provide more information on planetary systems;
Theory and Antartica meteorite finds will provide more information on planetismal formation;
Kepler mission will provide information on frequency of terrestrial planets; and
TPF/Darwin missions will characterize terrestrial planets around nearby stars.
Q: Could late heavy bombardment have been important? Don't know whether it was due to comet or asteroids?
Q: Chemistry of comets not as secure as stated
Q: The water delivery simulations are not self-consistent.
Q: Earth vs. Mars? comets/asteroids more important for Mars [because it is smaller], only a few could have delivered all of the water that Mars is thought to have or to have had.
Looked at the core accretion model, in which giant planets grow from smaller planetismals, with a focus on the gamma Cepheus system. Core accretion requires low relative velocities of particles, but companion star excites eccentricity of planetismals, producing large impact velocities, particularly for particles from outer parts of the disk. Companion star might have hindered planetary growth.
Ad hoc planetary disk truncation can solve this problem. Adding more gas to the disk can also solve the problem as it produces more gas drag on particles. This effect begins to be effective for particle sizes around 400 m, becomes substantial for 20-km size objects.
Described simulation, using 250 "embryoes." Can make planetary core in 10 Myr, but the core is in the wrong place, around 1.5 AU instead of the observed 2.5 AU. Could invoke migration of core outward, due to scattering from embryoes interior to its orbit. Not clear that this is efficient enough.
Could binary star system formed larger, then shrunk? Possible, but not clear why
Deplete inner parts of disk?
Implies that a gravitational instability formation mechanism is required?
Beckwith & Sargent found a distribution of protoplanetary disk masses, sort of. It is centered on the 0.01 solar mass value thought to be appropriate for the solar nebula, but it has at least a factor of 10 spread.
Estimates timescales of planetary formation. Finds relation between surface density of disk, distance from star, and kind of planet formed. Assumes a power-law density distribution within the disk and oligarchic growth, i.e., once a few large planetismals form, they dominate everything.
Suggests following scenario:
Massive disk: Forms Jovian planets that migrate and end up with large eccentricity;
Medium disk: Forms a solar system-like planetary system; or
Light disk: Forms only terrestrial and icy giant (Uranus, Neptune) planets because there is not enough material to form Jovian planets.
From the Beckwith & Sargent results, he estimates that those systems have disk masses less than 0.03 solar masses, so capable of forming terrestrial planets, are around about 60% of all stars.
Q: Didn't really take migration into account.
Q: Beckwith & Sargent result appropriate for T Tauri stars, with masses less than 1 solar mass. Also the luminosity is much higher for T Tauri stars. Neither of these effects taken into account.
Nelson studied binaries, with particular case of two 0.5 solar mass stars separated by 50 AU, with an orbital eccentricity of 0.3, and each with disks. Nelson found the disks were heated, even to the point that refractive elements began to sublimate [meaning that terrestrial planets could not form].
Boss repeated this simulation, using a 3-D radiative transfer code, and [slightly?] different initial conditions. He was able to produce planets, or at least clumps begin to form in the disks. He did not have to use an artificial viscosity in the disk, because of the radiative transfer, and he found a much shorter cooling time.
Concludes that tidal forces can produce disk instability, so binaries should have planets. Noted that this was the "right answer" as at least some binaries do have planets. Speculated that terrestrial planets might form.
Q: Could binary separation change? No, no reason to expect mass loss from system.
Restated that planetismal formation difficult. Suggested considering effect of vortices into protoplanetary. Expect to see dust trapped in vortices, allowing planetismals to form.
Conducted simulations of vortices in protoplanetary disks. Found "dust," or at least 1-m sized particles, being trapped in vortices. Larger or smaller particles not trapped as efficiently.
Also found that vortices destroyed by dust, and need to figure out how vortices form in the first place.
Q: 1-mm sized particles found in meteorites? Can't reproduce this.
Q: Vortex shearing? [which tends to destroy the vortices] Yes, it is an effect [and not really taken into account?]
Defines Earth-like planets as those with masses between 0.7 and 3 Earth masses. At the lower end of the mass range, it is not clear that plate tectonics can survive. At the upper end of the mass range, it is not clear that anything prevents a runaway growth to a giant planet. Also requires the planet to have a temperature between 0 and 100 Celsius.
Stated that the long-term goals are
Inventoring and characterizing exoplanets;
Detecting Earth-like planets;
Detecting planets in the HZs of stars; and
Conducting atmospheric studies of these planets.
Summarized planet finding methods:
Radial velocity method: limiting precision of order a few meters/second -> Saturn mass planet at 1 AU from star;
Transiting planets: [Limited by need for edge-on orbits];
Microlensing: Hasn't been all that successfull yet; and
Astrometric
Claimed from mass distribution of known exoplanets that expect 3% of stars to have Earth-like planets. [Is that number right? Error in notes?] Summarized some other statistics.
He mentioned briefly the case of HD 82943, which is too Li rich. Could this be due to planet swallowing?
Summarized mass--semi-major axis phase space for planet detection. Saturn is detectable by radial velocity or astrometry. Only hope of detecting Earth-like planets is via transits.
(Diverged briefly to show picture of F ring at Saturn from Cassini.)
Future missions:
COROT [ESA?]: Search for relatively massive planets and "big" Earths;
MOST (Canada): Results expected soon;
Kepler (?): 1-m telescope, high-precision photometry, long duration, few Earth-like planets expected to be detected;
Eddington (ESA): Cancelled, hope to revive;
GAIA (ESA): astrometry, could see Sun's motion at 100 pc, goal is 10--20 microarcsecond precision;
SIM (NASA): pointed interferometer, but survey thousands of stars;
TPF (NASA): actually two missions: TPF-C, a coronograph, and TPF-I, an interferometer [NASA representative later said both are important];
Darwin (ESA): like TPF-I, two may merge; and
Lifefinder and Earth Imager: way out concepts, many telescopes in space, each several meters in diameter.
Timeline:
2008--2012: gather statistics [Kepler, GAIA?, SIM?];
2015--2020: detection of a few Earth-like systems [TPF, Darwin];
Then: Lifefinder, Earth Imager.
He described a simulation of the Earth, specifically of the CO2 cycle, with interchange between the atmosphere, oceans, and crustal material. The issue was to assess whether there might be habitable planets within the HZ of 47 UMa, for which a terrestrial-mass planet could be dynamically stable if it were within 1.25 AU of the host star. He found that the HZ varied as a function of continental crust area, because he assumed that the amount of exposed continental crust was related to the amount of "weathering" or incorporation of atmospheric CO2 into the crust. He also looked at the long-term habitability of such a planet and favored "water worlds," in which a large fraction of a planet's surface would be covered by water.
Also looked at the system around 55 Cnc, for which he claimed that the HZ was quite large, potentially between 0.7 and 1 AU, and all orbits within this range would be stable.
Q: By long-term habitability vis-a-vis water worlds, he claimed to run the simulations for the life of the system (~ 1 Gyr).
Q: Didn't really explain why he favored water worlds.
Q: Dispute over whether amount of exposed continental crust is really the appropriate metric for determining "weathering." Exposed material, e.g., lavas on the islands of Hawaii [and Iceland?] are more efficient at absorbing CO2 than is much older rocks like those in Australia. Perhaps geologic activity is a better measure of weathering than simply exposed continental crust.
Presented a summary of the OverWhelming Large Telescope (OWL), a proposed 100-m optical telescope under study in Europe. One of the key issues is whether one needs a 100-m class telescope (i.e., OWL) or a smaller one like the TMT [Thirty-Meter Telescope or Twenty-Meter Telescope, depending upon one optimistic one is about budgets], now under study in the U.S. Claims that a 30-m instrument would be good for detectining Jupiter-like planets, but a 100-m is needed for terrestrial planets. The goal is to make the resolving power of the telescope (i.e., its diffraction limit) sufficiently high that the planet can be separated cleanly from the star's light. This of course assumes that one can make such a large telescope operate near its diffraction limit. One also has to make this measurement in the presence of considerable glare from the host star. He quoted contrast levels of 1 billion [which means he is thinking of visible-light detections instead of IR, I think]. Also, he claimed that if one believes that 30--50% of stars have Earth-like planets, in order to have a good probability of detecting such a planet, one would have to survey the solar neighborhood out to 30 pc, which again, he claimed pushes one toward a 100-m telescope rather than a 30-m telescope. Finally, both the TMT and the OWL would be composed of individual mirror segments, similar to the construction of the Keck telescopes. He claimed that the cost of mirror segments becomes increasingly cheap [by which I think he means that they become a smaller and smaller fraction of the total telescope cost] for telescope sizes larger than 60--70 m, another reason to favor OWL over TMT.
Discussed the science of Lifefinder, a proposed successor mission to the Terrestrial Planet Finder (TPF). Lifefinder would have the goal of determining the compositions of terrestrial-mass planets in the solar neighborhood.
How does one determine that life is present on a distant planet? He described a "sequence" for Earth [by which I think my notes indicate a time sequence, i.e., over the course of Earth's history]:
Atmosphere dominated by reducing compounds and CO2, as the result of significant volcanism.
Atmosphere contains significant amounts of methane (CH4), possibly as the result of anoxic processes and/or decay.
Atmosphere contains significant amounts of oxygen (O2) due to photosynthesis. Possible that both O2 and CH4 would be present simultaneously. There presence relies on the "equilibrium" state of the atmosphere, which is poorly understood.
Described how one would make these measurements. For O2 (and its byproduct, ozone [O3]), one could use measurements ranging from visible to IR wavelengths. For CH4, one would want to use measurements in near- to mid-IR wavelengths. However, he emphasized that these are demanding measurements.
He showed various spectra of Earth and pointed out that CH4 absorption could be quite weak and therefore masked by different conditions on different planets. He also described the "red edge" in the Earth's spectrum due to the strong reflection by chlorphyll in the near-IR, but indicated that this might not be of much use because Lifefinder is envisioned as looking at the integrated spectrum of the planet, so for the Earth the spectrum might be dominated by clouds and one would not detect plants on the ground. Tried to summarize briefly some Earthshine measurements trying to simulate measuring the integrated spectrum of a planet.
He argued that measurements in space are the only way to accomplish Lifefinder, even a 100-m telescope on the ground would not be sufficient. He argued for 30-m telescopes in space, probably multiple telescopes. He argued that one strong reason for 30-m class telescopes would be to gather enough photons to be able to measure and/or understand systematic effects in the telescopes.
He described Lifefinder as potentially being a 24th century experiment, not a 21st century one.
Q: Could CH4 or O2 be produced abiogenically? Yes, he cited the example of an ice-covered planet (e.g., a larger version of Europa) on which the ice is being photoionized to produce the oxygen, but there is no other surface material other than ice with which the oxygen can react and be removed from the atmosphere.
Q: He wants to be able to service Lifefinder in space. [Seems to be trying to tie Lifefinder to the recently announced NASA mission of returning to the Moon.]
Q: Dispute over fraction of planet's surface seen in Earthshine experiments. It may be as little as 10%, in which case detection of the red edge becomes possible to contemplate.
[The session chair indicated that the minor planet (9826) Ehrenfreund is named after her.]
Described "primordial soup" as containing ingredients from both abiogenic reactions on Earth as well as organic compounds delivered from space. She summarized stellar evolution and cosmochemistry as to how the essential elements (C, O, N, ...) are formed.
Organic compounds in space are formed in the interstellar medium (ISM). About 99% of the ISM is in the form of gas, with the remaining 1% in the form of dust. Chemistry is complicated and involves gas-phase reactions in the gas, solid-state reactions in the dust, and gas-dust grain interactions. One difficulty with the relevance of organic compounds in space to the origin of life on this planet is that the [most or all] organic compounds are formed in the molecular clouds that also give birth to stars, and the organic compounds are destroyed once the stars ignite. The relevant molecular clouds are the so-called "hot cores" in which the temperature is about 100 Kelvin, the density is about 107 particles per cubic centimeter, and the lifetime is about 100,000 years.
She summarized the carbon in the ISM. About 20% of it is in carbon monoxide (CO), less than 8% is in icy dust grains, and about 15% is in poly... aromatic hydrocarbons (PAHs), but this leaves a fair amount of the carbon unaccounted for. One possibility would be large, fairly rigid molecules as these would have only weak spectral lines. Such molecules might also be transported easily into forming planetary systems. She suggested that some organic material probably is incorporated into planetismals. During the late heavy bombardment, she estimated that 104 to 109 kilograms of carbon delivered per year to the Earth (exogenous delivery).
She compared comet chemical composition to stellar composition, because comets are presumed to be the primary means of delivery for organic materials. There is a large diversity in the chemical composition of comets. Comets are probably a mixture of both interstellar and nebular material. Some of the compounds found in comets or thought to be present, e.g., crystalline silicates, are almost certainly nebular in origin.
Described the Murchison meteorite, in which organic compounds have been found. A small amount of the organic compounds were [water] insoluable carbon compounds; there was also a small amount of voilates or biogenic compounds. She described how one might form these compounds by starting with cyanide and aceteldehyne and adding ammonia (NH3) or H2O, depending upon the pH level.
She re-measured the nucleobases in the organic compounds in the Murchison meteorite and claims that it is much different than the soil, thereby ruling out contamination. [However, I couldn't quite see how she arrived at this conclusion based on the table she presented.]
Even if one can deliver materials to the Earth, what was its early state? Would organic materials on the early Earth have been able to start life? We don't know what the state of the early Earth was. Probably atmosphere contained a large amount of N2, which she claims means it would be more difficult for the atmosphere to have been a source of abiogenic organic compounds.
She concludes that the amount of exogenic organic material (i.e., delivered) would have been roughly equal to the amount of endogeneous (i.e., "in-house") organic material.
Next problem is that, even if one has a sufficient amount of organic compounds, how are they concentrated in a manner such that life can originate? Could this be done underwater or would an ocean be too dilute?
Claims that the amount of carbon/organic material on Mars is far less than it should be if comets delivered a proportional amount to Mars as to Earth.
Future: continuing work on chemistry pathways for forming carbon compounds in the ISM. Even if one has the organic compounds, how easy is it to form life on early Earth?
Regarding a recent [and controversial] claim of the detection of glycine in interstellar space, she claims that that detection is now secure.
Claims that HCN has been overlooked by the community as an important molecule. Among its various properties are that it is easy for it to undergo polmerization.
Described a series of Miller-Urey like laboratory experiments starting from HCN. Claims that an HCN solution to which one adds [? ammonia?] produces huge amounts of organic compounds, some of which are H2O soluable and others not. Claims that the reactions produce peptides not amino acids, and that therefore proteins were produced before amino acids. Even if the laboratory experiments were conducted without H2O being present, still lots of organic compounds were formed.
Claims that tholins, a series of reddish organic compounds, are really HCN polymers. ["Tholin" is a term coined by Sagan to describe a series of organic compounds. They are produced easily in Miller-Urey--like laboratory experiments and have a characteristic reddish or brown color. They have been hypothesized to explain the reddish color of many icy bodies in the outer solar system, which would be covered in tholins produced from the ices bombarded by the Sun's UV radiation.]
Argues that popular view for the origin of life of an initial "RNA world" is wrong. Life would have started from HCN world, in which HCN polymers would form the basis for proteins and amino acids.
Described a study of interplanetary dust particles (IDPs). Wants these to be a means for delivering substantial amounts of organic material to the Earth.
There are lots of IDPs. The Long Duration Exposure Facility (LDEF) satellite got hit by lots of them, but they have a range of sizes. For IDPs larger than about 20 microns in size, they can get heated during their passage through the Earth's atmosphere. This can destroy their organic compounds. For sizes smaller than 10 microns, they effectively fall to the Earth without being heated, so these particles could deliver unheated organic material ("pristine").
He is analyzing IDPs. Traditional chemistry has problems with 1 nanogram particles. He is using a synchrotron light source and Fourier transform IR spectragraph. Finding lots of features due to C=C and C=O bonds, and some C-Hx compounds. The new results are from 5 IDPs, 4 of which are anhydrous (no water) and one of which is hydrated. Seeing lots of C=O features, as well as O- and N- compounds. The C/N ratio is about 12. With the FT IR spectrograph, was able to make a map of where the various compounds existed in the IDP. They could produce an image of the particle in the wavelengths of the N-absorption lines and outside of the N-absorption line wavelengths. Found an anti-correlation in that the carbon is not located where the nitrogen compounds are and vice versa.
Claims that IDPs are chemically different than comets (Halley) or meteorites (Murchison), with more O and more N. Suggests that 15,000 kg per year of unpyrolized (unheated) material falls to the ground in IDPs in the current epoch. Could have been much more in the past.
Described the "RNA world." [My notes have something about a "eutectic phase."] The importance of RNA is that it can carry out both protein (catalytic) and DNA (information storage) functions.
A eutectic phase can harbor compounds, allowing them to concentrate and form polymers. Described a series of laboratory experiments in which oligomers could be produced starting from an eutectic phase. Were able to produce 15- to 20-molecule length polymers. Claimed that if the eutectic phase were concentrated, could elongate these to 30- or even 45-mer molecules. However, salt water impedes this process. Wants origin of life to occur on land masses in order to avoid sea water.
The RNA world solves the DNA vs. protein (i.e., chicken or egg) formation problem. Suggests that the sequence was RNA -> RNase-P -> last universal common ancestor (LUCA) -> life diversity. RNase-P is a less efficient catalyst than protein but is more efficient than introns or some kineases. Notes that introns have an eukaryote aspect to them.
The traditional "tree of life" has bacteria and eukaryotes diverging from the LUCA, with the archea later diverging from the eukaryotes. He questions whether this is wrong, with confusion introduced by gene duplication. Could it be that eukaroytes and archea diverged from the LUCA, with bacteria diverging later from archea? He wonders whether eukaryotes might not be a basal part of the "tree of life." There are several what appear to be RNA-world artifacts that appear only in eukaryotes. However, there could have also been lateral transfer of genes, or eukaryote fusion could explain RNase P artifacts.
Many pykarotic species have large gene diversity. She showed an example of 3 genomes of 3 [close?] species, which shared only 39% of the same genes.
She focussed on Thermotoga, a deep phylogentic branch within the 16S rRNA tree of life. It is part of the bacteria part of the tree. It is widespread and thermophillic. [I believe it thrives at temperatures around 90 deg. C.] She speculated that it might be one of the earliest divering and slowly evolving species. However, it may have also undergone lateral gene transfer with archea.
Her approach was to hybridize a test species against T. maritina MSB8 strain (from a volcanic island off Italy [she didn't indicate which island, Sicily or Volcano?]), subtract genes from the test species and T. maritina, and look at what is left over.
[I learned later that 16S RNA refers to a specific part of the RNA that is responsible for encoding information from DNA. Because it has to interact with the DNA of an organism, 16S RNA is thought to be unique to each species.]
She found that there is a fair amount of gene diversity between various Thermotoga species, with much of the differences linked either to sugar transport or to an ATP-related gene [and therefore to energy storage]. This may represent a transfer from archea.
She posed an essential question: Does it make sense to make trees of species if there have been lots of gene transfers? Maybe it makes sense to make "gene trees." [What followed was a long discussion of various introns in various Thermotoga species, which I'm not sure I followed.] She concluded that various introns had been transferred from eukaryotes, specifically thermophillic eukaryotes. She concluded with multiple examples in which the linkage or relation between species depended upon the portion of the genome that one compares.
Q: Thermophyillic eukaroytes live at temperatures of 50--60 deg. Celsius. Why would a hyperthemophyillic species like Thermotoga acquire genes from thermophyillic eukaryotes [given the difference in temperatures at which they thrive]?
Q: With so much gene transfer, does it make sense to search for a LUCA? No, maybe one searches for a last universal common "community."
Claimed that definitions of life include aspects not unique to biological systems, e.g., "growing," as well as aspects unique to life. Talked a lot about bifurcation points. [I'm not quite sure I understood what he meant, but his use of the term "bifurcation point" seemed almost to imply something similar to a phase change in a physical system.]
Defined life in terms of compartments (membranes) and heritable information (DNA) and energy ([sugar?]). All life has membranes. Illustrated a common membrane structure consisting of a bilipid, in which two molecules are arranged head-tail like 'o- -o'. Here 'o' represents a hydrophyillic head to the molecule while '-' indicates its hydrophobic tail. [If I understand this, the hydrophobic part tries to prevent substances, particularly water, from crossing the membrane while the hydrophyillic part enables substances to cross when needed.]
She looked at the morphology of bacteria. Bacteria morphology has two broad classes, coccal (circular) or rod shaped, with a few intermixes. The most deeply rooted bacteria in the tree of life [so those presumed to be most primitive] are all rod shaped. However, if the shape of a species of bacteria changes from rod to coccal, it never reverts to rod-shaped.
She suggested the following sequence: evolution of cells walls peculiar to bacteria -> evolution of membrane transport but what environment suitable for primitive vesicular transport? [She also made comments suggesting that perhaps the coccal shape produces some evolutionary advantage, although it wasn't clear to me if she was attributing the advantage to reproduction or respiration being easier.]
Showed that she was able to produce "biomorphs," objects with a biological appearance, which she suggested might be confused with microfossils. The common composition is a silica skin covering these. [I believe that silica and barium were the crucial aspects for the formation of these structures.] She showed comparisons of a number of biomorphs with microfossils. At least to this untrained eye, the similarities were striking, although in a few cases the sizes differed (e.g., the biomorph was 2--5 times larger than the microfossil to which she was comparing it).
How does one determine a microfossil? It relies on appearance, dating rocks, etc. She suggested that many of the same criteria (though perhaps not all) could be met by biomorphs.
One key aspect is whether the Archean environment could have produced these biomorphs? It is not clear as some of the techniques seem fine-tuned, e.g., they form in pH values of 10--11, in high temperatures, and they need a ready supply of both organics and barium.
Q: These biomorphs appear with both L- and R chirality [in comparison to life which utilizes L chiral materials exclusively].
Discussed biocomplexity in terms of human civilizations. The study is being done on the Croatian islands of Krk, Hvar, Brac, and Korcula. These were all connected to the mainland until approximately 6000 BC at which point the rising Adriatic sea isolated them. His team is collecting biomedical and geneological data on the populations on the islands. The goal is to link genetic assocations to specific phenotype and genotype expressions.
[The bioastronomical connection seemed a bit tenuous. When he got around to talking about it, he seemed to be talking in terms of imaging habitable planets or even sending spacecraft to them.]
Described the island of Surtsey, a volcanic island that appeared south of Iceland on 1963 November 13(?). Eruptions continued until 1967, by which time about 1 km2 of magma was produced. Composition is in part [largely?] tephra, which is essentially solidified volcanic ash. Drill hole studies over the past 25 years show that the island is cooling at the rate of about 1 deg. per year. At its current temperature [about 250 deg.? IIRC], it will take about 100 years to cool, suggesting that this is the typical lifetime of a hydrothermal system.
There are microbes present. He suggested that they may even be helping to modify the rock/ash on the island, at least in the regions at lower temperatures. Also showed a picture indicating that a substantial amount of lichen or plant life has colonized the island.
There has been a significant amount of marine abrasion over the past 25 years. Maximum extent of the island was about 2.75 km2, it is now about 1.75 km2. Most of the loss is due to lava being eroded. [If I understood what he was saying, the island is composed of an inner "core" of extremely hard rock (tephra?) and an outer, more easily eroded rock. The outer portion is being eroded, while the inner portion will probably last for considerably longer.]
Claimed that photosynthesis was probably due to the symbotic inclusion of bacterium into eukaroytes [which I gather is the canonical view]. Photosynthesis is important in the overall energy budget of life on the planet.
There are 5 photosynthetic bacteria, only one of which is oxygenic. The various species are not closely related. The five are cyanobacteria, purple sulfur/purple non-sulfur bacteria, green sulfur bacteria, filamentous anoxygenic bacteria, and phototrophs. Of these, cyanobacteria are the oxygenic [and the ones responsible for polluting the atmosphere with O2 about 2 billion years ago IIRC].
There are 2 different reaction centers [in the cells or in the genome?] for photosynthesis. The reaction centers seem to be distributed randomly throughout the five groups, with cyanobacteria having both reaction centers. He wants aspects of photosynthesis to be due to lateral transfer after the divergence of the various species of bacteria.
There are two competing models for the origin of life, a cold "primordial soup" at a temperature of less than 50 deg. C and a hot "primordial soup" at a temperature of more than 80 deg. C. If biogenesis was cold, how could the LUCA be hyperthermophyillic? One possibility is that there was impact or climate sterilization of the planet so that only the hyperthermophiles survived.
There is evidence of liquid H2O some 4.4 Gyr ago. [I think some of this was presented in Bioastronomy 2002.] However, there is also evidence that the planet's temperature, at least in some spots if not an average temperature, was above 80 deg. C at 3.8 Gyr ago. He claims that if the average climate was hyperthermophillic/thermophillic, then there is nowehere, even on the tops of mountains, that would have been mesophillic [T ~ 50 deg. C]. He looked at the branch length of various microbes from the LUCA; he claims to find a strong correlation between the presumed nearness to LUCA and the temperature at which the organism thrives. He claims an extrapolation of this trend suggests that the LUCA thrived around 120 deg. C [which is near or at the record for the most hyperthermophillic organism known currently].
Hot biogenesis has both pros and cons. A difficulty with it is that RNA and DNA are not stable at high temperatures, at least in experiments carried out in pure H2O. However, H2O with salts in it can stablize RNA and DNA. [He didn't really discuss other pros and cons.] He favors biogenesis at hydrothermal vents on the ocean floor [so hot biogenesis], with compartmentalization provided by clays or condensates. Archea (which thrive at T ~ 120 deg. C) and bacteria (thriving at T ~ 100 deg. C) emerging separately. He claims that various oxygen isotope evidence suggests that the average ambient temperature on the planet has been descreasing over time and that the times of emergence of various microbes is consistent with when the planet had cooled sufficiently that the microbes could survive.
He discussed Raman spectroscopy, particularly as it applies to microfossils. Raman spectroscopy consists of shining laser light on an object. Most of the light is scattered, but about one-millionth of it emerges in a form from which one can determine the roto-vibrational spectrum of it, thereby obtaining its composition. However, his talk was also a defense of the identification of microfossils, with an emphasis on the suite of techniques used to identify them. [I believe this is due to the recent challenge to some of his work that some of the microfossils that he has identified may not be microfossils but abiogenic. He mentioned Carnerup by name, indicating that he did not think that biomorphs would be confused with microfossils.] Among other things, Raman spectroscopy helps confirm that specimens are microfossils because the spectroscopy responds only to the biological material.
Q: Cannot do carbon isotopes studies using Raman spectroscopy [which would help cement the case for microfossils, because life uses the lighter 12C isotope preferentially over the slightly heavier 13C] but he thinks he can do it using another technique.
He summarized racemization, the process by which a set of molecules of one chirality is converted to a set containing roughly equal mixtures of left- and right chirality. Essentially left-handed and right-handed [called either L and R or L and D] molecules represent local minima in the energy configuration of a molecule. Given sufficient, but not too large, additions of energy a molecule can convert from L to R or vice versa.
Posed the question of whether racemization could serve as a crude dating method. In general it cannot. For instance, in crystalline structures, racemization can stop entirely. Given that chiral molecules are taken as a clear biomarker, the objective when searching for life on other planets should be to look in places that may have experienced rapid dessication [drying] as this would have "frozen" in the L/R ratio. In other words, on Mars, one does not want to follow the water!
He favors a strategy of searching in ice or permafrost as either is probably a slowly changing environment in which any unequal L/R set of molecules would have been preserved. For the Earth, he claims that effectively 85% of its surface is at a temperature less than 4 deg. C. He has looked for frozen organisms in the Siberian permafrost. He claims that some Martian landscapes look like permafrost. Even at -12 deg. C, he was still able to find metabolic activity. He also made a reference to possible microbial activity in Lake Vostok.
[He works for a company called Prokaria, a take off on prokarotye.]
Iceland has a range of extreme environments, e.g., hot pots, high sulfide regions, boiling mud pots, pH levels of 1--2.5, T ~ 80--100 deg. C. In a typical hot pot or mud pot, organisms range from anaerobes (thriving at T ~ 100 deg. C) to sulfolopus (living at 90 deg. C, and often seen as a slick on the surface), Cyanidum (at 55 deg. C) and Zygognium (at 20 deg. C). The latter two are both eukaroytes. Hot pots provide lots of free energy and organic chemicals. He also showed pictures of hot springs, areas with lots of H2O, again in which life thrives. He summarized Prokaria's efforts to understand and exploit the chemical capabilities of these organisms.
Only 8 elements comprise about 99% of the Earth's composition. Most of the Fe and Ni is in the core while the mantle is mostly Mg and Si. Adding H2O to a Mg- or Si-rich rock produces serpentine in a process called serpentization. It's actually fairly complex chemistry, in which compounds like olivine or enstatite are converted to serpentine (and other compounds).
His focus is on the Mariana trench, the region where the Pacific plate is diving under the Philipine plate. The subduction region forms a broad arc, and right at the interface is a region called the forearc. Within this forearc are a series of mountains. In classical geology, mountains are formed only when plates collide, so what are mountains doing in a subduction region?
As the Pacific plate subducts, the water is heated out of it. It moves into the mantle, forming serpentine. The serpentine then rises up to form the mountains; the mountains are essentially serpentine mud volcanoes. [I think this means that the serpentine is less dense that the average mantle rock.] These are cold volcanoes, but they have measured flow from them so they are volcanoes in the sense of rock flowing forth from them. They have a structure of a central chimney, up which the serpentine is flowing, surrounded by material that has emerged previously. [The drawing in my notes suggests that they are rather like shield volcanoes.] Also there is a gradient in composition across the Mariana forearc, again consistent with this picture of serpentine formation by extraction of water from the subducting plate.
Organisms have been found living in the surroundings, where the volatiles ooze out of the volcanoes. The region has a high pH, about 12.5, but it is effectively a cold spring. It is the highest concentration of acid-loving species known. There is lots of inorganic chemistry across this region that produces CH4, through the serpentine. This could be fuel/food for some of the organisms.
Q: Either the organisms or the inorganic chemistry related to outgassing volcanoes could explain the CH4 detected recently in the Martian atmosphere.
Looking at subsurface life. They sampled a series of boreholes around Reykjavik and found numerous subsurface organisms. Many diverse communities found, with not a lot of similarity to surface organisms. Many unidentified organisms or gene sequences. About 21% of the communities are common to all boreholes, about 22% are unique to each borehole. Somehow need to distribute organisms in subsurface to have commonalities. Claims that Iceland appears to have many underground channels, particularly for rainwater seeping down. It would take about 10,000 years for rainwater to perlocate through these underground channels.
[This led to one of the more humerous Q&A sessions. He had referred to the water as being "meteoric" in origin. The astronomers were quite confused as to whether he really meant, delivered by extraterrestrial rocks. To a geologist, though, meteoric water means "rain water."]
He emphasized that there are many different things that can lead to an organism being classified as an extremophile. It could be its shape, the atmospheric conditions under which it thrives (e.g., can the organism tolerate oxygen), the pressure, the temperature, .... Some extremophiles can tolerate multiple extreme conditions, so-called polyextremophiles. He summarized the range for certain extremophiles. For temperature, he claims that organisms have been found that can survive in the range -15 deg. C < T < 115 deg. C. [I think there was a recent publication claiming survival of a species up to 121 deg. C.] Leads to various definitions of temperature survivability, hyperthermophile, thermophile, mesophile (T ~ 50 deg. C), and psychrophile (T ~ -10 deg. C). For acidity, the range on organisms is for pH levels less than 1 to as high as 12.
He summarized by noting that within the range of conditions seen on Earth, these organisms could survive on Mars, given sufficient liquid H2O. He also surveyed other spots in the solar system for extremophiles.
Why is life chiral?
Trying to construct polymers from monomers of different chirality is difficult. He used examples like the following to illustrate this. Consider a polymer consisting of L-L-L. It can accept another L monomer, becoming L-L-L-L. However, adding an R monomer terminates the chain, L-L-L-L-R cannot grow any longer, at least by adding monomers on its right end.
He constructs a model describing this. Cross-inhibition is the process of adding an R monomer to an L polymer (Ln) to form LnR1.
He introduced the concept of auto-catalysis, in which L monomers are produced from Ln polymers. [I didn't understand this part.] He then introduced the fidelity f, the efficiency at which auto-catalysis occurs. So f is essentially a free parameter, taking on values ranging from 0 (no auto-catalysis) to 1 (perfect auto-catalysis). He found that if f is low, then one has an mixture of approximately equal parts L and R monomers. However, if f exceeds about 0.5, then one quickly approaches strong chirality in which the mixture is essentially all L or all R, a process that he termed "bifurcation."
[Q: I asked a question on this, because I don't understand what the motivation for this study is. It seems to me that if one has a free parameter that allows one to make more L or R monomers, then it's quite easy to see that one should approach rapidly a state in which the mixture is either all L or all R. I wondered if this was just a strong argument for an external cause for life's chirality, e.g., star light polarization. He disagreed.]
He summarized da Vinci's attempt to define water. Not having a molecular understanding of water as H2O, da Vinci was clearly frustrated. He suggests that we are somewhat in the same state today because we are not able to produce any complete definition of life. He distinguished between definining life vs. habitability of life as we know it vs. the origin of life.
He focussed on Europa, with an attempt to explain how we know what we know.
From Earth-based spectroscopy, we know that the surface is nearly pure H2O ice.
The crater count on the surface from the Voyager flyby was quite low, indicating a relatively young surface (< 50 Myr, for comparison the Earth's ocean floors are about 100 Myr old).
The Galileo NIMS instrument showed a near-uniform distribution of the near IR bands of H2O, consistent with mild contamination of the ice with MgSO4 salts, or H2SO4, or even bacteria.
The bulk density is about 3 g/cm3. This is consistent with taking Io and adding about a 100 km deep ocean. Moreover, Galileo trajectory data are consistent with an 80--170 km deep ocean.
Most of the information on the internal composition and structure of Europa comes from the combination of its bulk density and the gravity measurements from Galileo, from which one can derive a moment of inertia. One tries to model Europa as a combination of a core (largely Fe), rock, and ice. That's how one arrives at an ocean depth somewhere in the neighborhood of 100 km.
However, the "ocean" could be in the form of liquid H2O or "warm" ice. Either would be consistent with the amount of tidal heating thought to be produced by the orbital resonance in which Europa finds itself. Galileo also measured a magnetic field, induced by Europa's motion through Jupiter's magnetic field. In order for a magnetic field to be induced, the interior of Europa must contain a conductor. The most plausible conductor is a liquid ocean containing salts. Claims that the most plausible salt is MgSO4 [based on abundance IIRC], which is also consistent with the surface spectrum.
He described work to try to constrain the amount of salts in the Europan ocean. Found the most likely range to be between 1.3 and 115 grams of MgSO4 salt per kilogram of H2O. For comparison, in the Earth's ocean the concentration is 2.5 grams of MgSO4 salt per kilogram of H2O. He concludes that any Europan life need not be halophillic [salt-loving], though some halophllic life from Earth would be able to survive in the conditions in the Europan oceans.
He summarized various sources of energy within Europa. These include charged particles hitting the surface of Europa [which could then be circulated into the ocean if the surface is convecting in any manner, I think he described some of this work at Bioastronomy 2002], hydrothermal vents, or the decay of 40K and the dissociation of H2O. However, the decay of 40K may not be important if the concentration of MgSO4 is toward the low end of his range.
He is quite concerned about the forward contamination of Europa.
He also suggests that Europa may be a resolution of the faint early Sun paradox: Don't try to keep water liquid on the Earth's surface. Allow the surface to freeze over and for life to originate underneath it.
He concluded with a few remarks on Titan, saying that it might be a good "laboratory" for organic chemistry. It might also tell us about whether life could use NH3 as a solvent or even in non-polar solvants like ethane.
Q: Why Mg salt, given that on Earth, Mg is not soluable in H2O?
Q: Where else could H2O be? Ganyemede, Callisto, Titan? even large asteroids, given that they might contain enough radioactive materials to raise the temperature and melt any ice in their interiors? However, large asteroids don't appear to show any signs of complex chemistry consistent with this notion, even if the H2O lasted for as long as 108 years.
Addressed the issue of planetary protection, which has two facets: protecting other planets from exportation of terrestrial life and protecting the Earth from importation of alien life. The difficulty is how to accomplish this given that alien life may take unexpected forms. For instance, the life around hydrothermal vents was not expected to be found on the cruise in 1977(?) that first found it ("otherwise there would have been more biologists on the cruise").
Most of the focus was on Mars, which he described as potentially being in an interglacial period. [It's not clear if that has a bearing on planetary protection per se.] He summarized the Phoenix Scout and Mars Science Laboratory missions, both of which raise significant protection issues.
He also summarized the protection tactics used for previous missions to Mars. Viking was baked for 54 hrs in a casserole dish, which makes it the current gold standard for trying to make a spacecraft organism-free. Less stringent methods were applied to Pathfinder, only an inventory of microbes on it was taken. [He may have also mentioned the immolation of Galileo in Jupiter's atmosphere in an effort to protect Europa.] He also described the planetary protection protocol developed by COSPAR.
Q: How do planetary protection methods compare to medical sterilization procedures? Planetary protection methods specify a reduction by 1 million [in the density of microbes] on a spacecraft while medical tools specify a reduction of 1 trillion [in the density of microbes] on surgical equipment. [In other words, medical procedures are 1 million times more stringent.] On the other hand, he also emphasized that medical tools are far more simple than spacecraft.
Described a series of experiments to test energy availability for life on Europa. The surface of Europa is 85--128 K, there is a large UV flux, and intense particle bombardment. His focus was on electron bombardment. They deposit most of the energy and penetrate deepest into the ice. By comparison, the UV flux penetrates less than 1 micron and ions penetrate about 10 microns, while electrons penetrate about 500 microns. If there is some means of "stirring" the ice, the products of the electron bombardment could penetrate to 1 meter.
The work has been in the Minos lab (so named because Minos was the offspring of Zeus and Europa). They grow [organic?] films, then bombard them with 10 keV electrons. One hour of exposure in Minos is comparable to 6 Europan orbits.
He focussed on hydrogen peroxide, as it is a potential energy source. They obtain H2O2/H2O ratio of 0.3 to 0.5% by number, with more H2O2 being produced at lower temperatures.
These results imply that if the upper 1.3 meters of the Europan surface is 0.3 to 0.5% of H2O2 by number, with enough resurfacing in 10 million to 100 million years, the oxygen levels [in the Europan ocean] could reach levels that would support terrestrial life. Some terrestrial organisms can survive at levels of less than 22 millimoles of oxygen.
Pointed out that the search for life on other planets would probably focus on searching for biomolecules. He described likely biomarkers as PAHs, amino acids, and fatty acids; other possibilities include naphthoquinones or quinones.
He described lab work on the UV irradiation of compounds thought to be similar to interstellar ices. He can make PAHs in inorganic chemistry. From these, can produce ketones and, by adding a hydrogen atom, could form complicated organic molecules inorganically, so these may be weak biomarkers, particularly if found in interstellar space.
He claimed that poor biomolecules would be free molecular species, e.g., PAHs, unless somehow out of equilibrium (e.g., left/right-handed asymmetry). He also stressed that alien life may not have the same biochemistry as we do. He illustrated a wide range of biochemistries, using only terrestrial life as examples.
He described UV light, ion, and electron bombardment of ices. The resulting processes for chemistry are sputtering, structural changes, implantation, residue, and chemistry. As an example, the OH band stretch can be affected by ion irradiation.
He argues for ion impact on Europa producing hydrogen peroxide. Described lab experiments in which H2CO3 produced, using both proton and helium nuclei irradiation. However, he also claimed a limit to the extent to which ion irradiation could produce changes, e.g., sulfur irradiation of water does not produce SO2 or HSO4 or .... [I'm not sure I understand. Seems to suggest that ion irradiation is not important, therefore.]
Also talked about CO2 irradiated by protons and helium nuclei. Seemed to indicate that the presence of CO2 could increase the H2O2 production with increased ion fluence because more O available. Spent a fair amount of time discussing H2O2/CO2 mixture as an possible starting point for chemistry in the Martian polar caps.
Described four different pictures of Mars: a dry Mars, a locally wet Mars, water vapor on Mars, and a cold, icy Mars. [My pen ran out of ink here, so this talk is sketchy.]
The picture of Mars as a dry place arises from images and spectra of Mars from various orbiters. In particular, he showed landscapes in which a particular type of rock was exposed. This kind of rock is not formed or does not survive in the presence of liquid water, so its presence means that there could not have been liquid water around it. Moreover, he showed places where this kind of rock was exposed over separations of many kilometers, yet the elevation of these exposed rocks was the same to better than 50 m, indicating that this is a wide-spread layer of rock with a common origin. His conclusion was that globally there has not been much liquid water on the surface of Mars.
Locally, however, there are deposits of hematite. Hematite forms naturally [though not exclusively?] in the presence of water. He concluded that there were some fairly small regions where there had been significant amounts of liquid water.
He didn't spend much time discussing water vapor, though there certainly is some in the Martian atmosphere. [This might be related to the idea that the amount of water vapor in the atmosphere varies depending upon how it is being heated.]
The cold, icy Mars might be like what we see today, in which substantial amounts of water are locked up in the Martian polar caps.
Asserts that the big question with respect to Mars is, Is there water on Mars?
He argues for a cryosphere [a region of permafrost], about 5 km deep over the entire surface. This cyrosphere would probably be concentrated toward the poles. Below the cryosphere would be a global aquifer, down to 10 km; below 10 km the rocks are too compactified to allow water in them.
He raises the question of whether the cryosphere might contain cryophillic organisms. Below that potentially could be a troglodytic [cave-like] region in the global aquifer. If so, there might be troglodytic organisms in the global aquifer [similar to cave organisms on the Earth, in which they do not use sunlight directly to survive?].
He argues that Mars' orbital variations lead to large climate change. In contrast to the orbital variations experienced by the Earth, Mars can have, for example, large fluctuations in its obliquity. [I believe Mars' obliquity can potentially exceed 35 degrees, in contrast to the Earth's 23 degrees.]
He argues that Mars is currently in an interglacial period. He summarized observations of Mars' surface: Poleward of +/- 60 deg. latitude, the surface is smooth and consistent with ice in soil. He argued that this ice-rich layer was deposited recently, and that the soil is now being dessicated because the obliquity is lower today than in recent past.
In his scenario, 500 kyr ago, Mars would have had meters of ice and dust down to +/- 30 deg. latitude. In his view, Mars' climate change is driven largely by obliquity changes. During times when Mars has a large obliquity, the poles are heated more efficiently. This leads to the somewhat counter-intuitive result that Mars has warm polar regions during glacial periods but cold polar regions during interglacials.
Is there any way to get material from the global aquifer to the surface? He pointed out a number of large cracks in the surface in the [...] region [somewhere in the mid-latitudes]. He argued that these cracks would form dikes, which could crack cryosphere within past 10[?] kiloyears. The result could be that material from the global aquifer could be brought to the surface.
[See also his second talk later in the meeting.]
He summarized the goal of the Mars rovers Spirit and Opportunity: Determine the history of two sites on Mars that might have been favorable to pre- or biotic conditions. He then described the rovers themselves and showed some of the first images.
He focussed on the rock outcropping in the first images of Eagle Crater. Do the rock outcroppings represent layered rocks and cross-bedding? He pointed out that rocks themselves are really only 20--30 cm high; images are sometimes deceptive in making them appear larger than they really are.
Three lines of evidence point to these rocks being formed by or modified by water deposition:
"blueberries";
"vugs"; and
the layered appearance.
Blueberries are typically 4--6 mm in diameter, spherical, and contain hematite. He showed images of rocks, which appear definitely layered, and from which the blueberries are being eroded. He described the cross-bedding of the rocks as being festoon cross-bedding, which is indicative of water not wind. He showed a number of such images, and continued to make this assertion, that the rocks must have been laid down by water not eroded by wind [though he didn't exactly explain why this is the case].
[I didn't quite catch the description of vugs.]
He discussed the rock abrasion tool (RAT) and illustrated some of the holes made in rocks by the RAT. Some of the holes have red appearance, consistent with blueberries being abraded and scattering hematite.
He also showed fissures in Mars' surface. He compared with the Martian images with those from the Arizona where fissures resulted from extreme dessication at the end of Dryas time. These fissures are "giant dessication cracks" and result from the dehydration of a lake. The shrinkage of the surface material during dessication results in rupture of surface.
He concludes that Meridiani Planum was a standing body of water.
He then switched to Endurance Crater. This crater is is 7 m or so deep, much deeper than Eagle, and being explored currently by one of the rovers.
He noted that the Columbia Hills are unexplained. He posed, but never answered, a number of possible origins: They could be an old crater rim, an interior crater deposit, or a volcano.
There is a fair amount of unknown or poorly explained rock weathering seen. He suggested that moisture has played an important role. He also suggested that the rock named Pot-of-Gold might be quite porous.
Finally, both rovers are about 180 sols into mission, which is well beyond their warranties. The current long-range plan for the rover at Gusev is to winter over on Husband Hill.
He posed the question of whether terrestrial microbes and microbial communities could survive if they were moved to a simulated Martian environment? How do bio-molecules degrade under Martian conditions? What conditions would improve their survival chances?
He described a series of experiments to examine survival (colony formation), activity (respiration measurements), and diversity (molecular fingerprinting) to assess the response of communities to simulated Martian conditions. They used mid-Jutland and Salten Skov soils that are thought to be Martian analogs. It was not clear if they added iron oxides. These are forest soils, so they contain many spores. These first set of experiments was not quite an exact Martian analog as the ambient pressure was 12 mbar instead of the 6 mbar at the Martian surface.
Their experiment looked at exposure of 8 sols (Martian days). They found that colony formation of the microbes did not appear to be affected by exposure nor were activity or glucose metabolism affected for microbes below 1 cm or so of the soil. Finally, there is little difference in the genetic composition of communities after exposure.
[I didn't quite understand this. They seemed to be changing just one thing at a time, e.g., freezing the sample or putting it below the soil, but they way that it was described, it doesn't seem that they are considering microbes below soil at Martian temperatures.]
He concluded that the incubation time was too short to see much effect. Moreover, much of their sample was in form of spores that are quite hardy, so their results may not be representative of more general microbe populations.
He pointed out that it will be another 10 yrs before sample-return mission to Mars, but 80 kg of Martian meteorites already on Earth's surface in the form of Martian meteorites. The focus is on ALH84001.
They are looking for biomarkers, and specifically looking for a biomarker that is difficult to be produced inorganically.
Magnetite is an inorganic material, but some kinds are produced by magnetotactic bacteria. How old are magnetotactic bacteria? There is no consensus, some researchers consider them to have evolved recently, but they have evolved as long as 2 Gyr ago. Magnetotactic bacteria can grow chains of magnetic particles.
A biogenically-produced kind of magnetite is MV-1 magnetite. It has 6 properties that are unique(?) to magnetotactic bacteria:
single domain;
chains;
unusual crystal shape;
chemically pure;
intact lattice; and
[E111] elongation.
However, he then noted that not all terrestrial magnetotactic bacteria produce magnetic particles that meet all of these criteria.
He summarized the history of the meteorite ALH840001. The rock itself is about 4.5 Gyr old. About 4 Gyr ago, it had some interaction with water. It was frozen until about 15 Myr ago, when it was ejected into space. It spent most of those 15 Myr in space before landing in Antarctica.
He focused on carbonate globules within the meteorite, which he described as quite unusual. They are cylinder shaped or zoned, and they sit in surface on crack surface. The magnetites are in these carbonate globules.
About 25% of the ALH84001 magnetites satisfy 5 of 6 criteria above. They cannot identify particle chains given the way they are disolved out of carbonate globules. [Does this mean that they are eliminating one of their criteria?]
It also can be difficult to identify the 3-D shape, given 2-D images. They used TEM [tunnelling electron microscopy] to try to identify shape. They claim that they have been able to confirm geometry of the magnetites as meeting one of the criteria.
He also argued that carbonate thermal decomposition is not a good way to produce these magnetites, and that they therefore must be biogenically produced.
He summarized Mars missions planned by NASA [and ESA] over the next decade. Mars missions are launched every 2 years to take advantage of the orbital mechanics between the two planets. Thus, there are missions planned in 2005, 2007, 2009, and .... The mission in 2007 is Phoenix, a lander in the Mars polar regions. [I didn't note what the ones in 2005 and 2009 are, but I think they are both orbiters.] He raised the question, What of the next decade?
He showed pictures of gullies on Earth and what appear to be gullies on Mars. They look strikingly similar, although their ages are quite different. He also showed images of what appear to deltas on both planets. In constrast to gullies, which can be cut by small amounts of water, deltas require large amounts of water over long periods of time.
With one of the upcoming missions, Mars Reconnaissance Orbiter [2005?], he emphasized that one of the limiting features in understanding its images is that we don't have a good enough understanding of potential terrestrial analogs. He also discussed Phoenix in the same vein. He again closed with the question, Where to go in the next decade?
[Portions of Garvin's talk seemed to be trying to justify NASA's new exploration policy.]
[I note here that many people, probably including Garvin, but certainly many others, made the point that the term "extremophile" is quite an anthroprogenic view. "Extremophiles" would describe us as unusual. While this is true, I don't quite see how it is relevant. We know that there is a severe bias in trying to find life. We know how to find life as we know it; finding life as we don't know it is really hard.]
He summarized the differences between Earth and Mars. In brief, Mars is a cold, dust desert without a magnetic field, which could provide protection of its atmosphere and from cosmic rays. He enumerated the following challenges for life on Mars:
The surface is exposed to a damaging UV spectrum. However, life might be able to evolve a protective sheath or to life sufficiently deep in the soil that it is shielded.
Ionizing radiation hits the surface. This might be less of a problem, as some shielding is provided by the atmosphere and soil.
The essential elements---C, H, O, N, P, and S (CHONPS)---are all present, but the abundance of N and P are uncertain, and they may be chemically bound in such a way as to make it difficult for life to access them.
Life as we know it also requires trace elements such as Na, Mg, K, Ca, and Cl and co-factors such as Fe, Mn, and Zn. The soil appears relatively uniform [in these elemental abundances?] across the planet based on the analysis from 5 landers. However, there may be places where these elements reach toxic levels.
It is not clear that sufficient organic chemicals exist on Mars. Howwever, not all organisms require organic chemicals, and Viking is not the last word on the organic chemical abundance. Moreover, there could be organisms in the polar ice.
The oxygen concentration in the Martian atmosphere is quite low, perhaps 100,000 times less than in the Earth's atmosphere. However, that could just mean that anerobes are required, after all, there was not much oxygen in the terrestrial atmosphere for the first 2 Gyr or so. Also, oxygen is available on Mars, it's just not in the atmosphere.
There are harsh oxidents in the soil and atmosphere. However, life may have evolved protective shells or developed enzymes for dealing with these. Again, life on Earth manages to survive in the presence of oxygen.
It is not clear what energy sources could be tapped by life. Phototrophs [light-loving] organisms might survive in the soil, deep enough that they are shielded from the UV radiation but shallow enough that they still receive some light. Chemolithoautrophs [chemical/rock-loving] organisms might be able to utilize a sulfate solution or there might be methagens, particularly given the recent discovery of methane on Mars. Many of these ideas are relatively unexplored, certainly not checked by Viking.
The climate is cold. The boiling point of water, because of the low atmospheric pressure, is 5 deg. C. However, psychophiles [cold-loving] organisms might survive. Also, there could be local warm spots.
There can be high salt concentrations in the soil. The soil is high in sulfates, with concentrations reaching 12%. It is not clear how saline the soil would be though if the water frozen in it were to melt. Extreme halophiles [salt-loving] organisms on Earth can tolerate 150 g(salt)/kg(H2), however, the salts on Mars are not dominated by sodium salts. Eagle Crater shows a gradient of Br, consistent with it being the result of evaporation. Endurance Crater is also starting to show a Cl gradient, again, potential evidence for evaporation.
The environment could be quite acidic, due to volcanic outgassing. For instance, can add sufluric acid to water and keep the water liquid down to -74 deg. C. He suggests the possibility of acidophilic onotolerant[?] psychophillic organisms. [ :) ].
Finally, where is the water? In Gusev crater, Mazatzal rock shows a high Br content, consistent with liquid water filling the rock's cracks with salt. He also showed pictures of the neutron hydrogen emission, which is thought to trace the water deposits on Mars. However, he also pointed out that the water had to be biogenically available [i.e., that it did not cost more energy to acquire the water from the environment than an organism could use the water to make]. For example, clays require a 14% water content for the water to be biogenically available, but a loam would be consistent with the neutron emission. He also pointed out that Meridani might the remains of an old lake.
He summarized that the soil, a deep aquifer, and [...] might serve as potential habitats. Alternately, one could take the fairly pessimistic view about life on Mars or one could take the optimistic view.
He summarized and compared the atmospheric properties of the Earth and Mars, particularly in light of the recent discovery of methane in the Martian atmosphere.
On Earth there would be no CH4, NH3, N2O, [...] if life were not present. He showed examples of what the concentrations of these various gasses should be in the atmosphere versus what they are. For instance, the amount of CH4 should be 10-145 moles in the terrestrial atmosphere. It is 10-6 moles, so it is enhanced by a factor of 10139. In a similar fashion the concentration of NH3 is enhanced by a factor of 1050.
For Mars, he estimated the atmospheric compositions for different temperatures assuming chemical equilibrium. He finds many of these molecules are at concentrations of 10-100 moles.
There are lots of ways to destroy these molecules in the Martian atmosphere, e.g., UV radiation, and it happens quite quickly. The lifetime of CH4 might be as long as 300 yrs, but for many species it is much shorter, down to only days or weeks.
He mentioned various detections of methane in the Martian atmosphere, by both ground-based telescopes and from Mars Express. The level is about 10 ppbv [parts per billion by volume]. Jikastiy has proposed CH4 as a greenhouse gas on the early Earth. Also, CH4 can be utilized by methagens.
He concluded by describing Ares, essentially an unmanned aerial vehicle (UAV) on an airborne mission to explore the Martian atmosphere. It lost narrowly to Phoenix Scout. It would have also provided regional scale/moderate resolution images of Mars.
[I talked to him a bit more later. I believe that the wingspan of Ares would have to be no more than about 16 ft in order to fit in the shroud, and they've already performed one deployment test in the terrestrial atmosphere.]
He emphasized the importance of climate on the Martian biosphere[!]. He wants Mars to have have had lots of standing water. [How does one reconcile this with Christenssen's talk?]
He poses the question of whether there is any evidence for ice in the equatorial regions. This would be evidence for an orbital dynamic impact on climate. Specifically, if the obliquity of Mars was high, then the poles would warm, evaporating/sublimating the water, and it would condense in the relatively colder equatorial regions.
He showed images of the Tharsis region, specifically around Arsia Mons that show deposits similar in morphology to those in Antarctica. He identifies drop mounds, sublimation tills, and rock glaciers. In effect, he was describing tropical glaciers on mountains. [Even to my untrained eye, some of these pictures were striking. Side-by-side, one could almost believe one was seeing two slightly different pictures of the same region.]
He argues for a wide range of caldera ages in the Tharsis region. Many are over 100 Myr old, with some potentially as old as 2 Gyr.
He also showed comparisons of Olympus Mons and the Makspier[?] glacier in Alaska. Some of these calderas may be as young as 10 Myr.
He argues that, if the climate models for Mars are even close to correct, one expects to find condensation of water around the Tharsis region.
He showed images of lobate deposits around hills. Are these essentially glaciation consisting of more than 50% ice? Some of them appear to have channels coming out of them. [Again, some of these were extremely striking images.]
He summarized his team's recent discovery of methane. They put a spectroscopic slit of a telescope across the face of Mars. They differenced spectra [from different times of the year so that Mars would have different Doppler shifts] in order to remove telluric lines.
They detect the CH4 R1 line. It is observed at multiple times, with the appropriate Doppler shift. Moreover, the air mass [amount of air through which one is looking] on Mars is such that most of the source of the CH4 is probably near the equator.
[This was also the end of the special session.]
Iceland has a form of basaltic sand that produces a spectrum similar to that produced by Martian soil. He described experiments of mixing in 5% by weight of red dust, approximately 2 micron particle sizes, with basaltic sand and the resulting spectrum is essentially unaltered from a pure basaltic sand spectrum.
He discussed the magnetic properties as well. He thinks that one might be able to explain the anomalous magnetic regions on Mars as due to a high oxidation state of the lava.
He described WetCHEM, a proposed in situ measuring lab for future Mars landers.
[Missed the introductory remarks]
He provided largely an historical overview. He claims that even before the Apollo missions we had a good understanding that the lunar maria were formed early. He showed a paper from 1966 in which he argued that the lunar maria were roughly 3.5 Gyr old, quite similar to their currently estimated age. Moreover, the highlands are far more heavily cratered than the maria, implying that there was a lot of cratering occurring in the first 1 Gyr or so of the Earth and Moon's history. Thus, by 1970, he claims a fairly good handle on the early history of the Earth and Moon.
One unsettled question, though, was whether there might be (small) reservoirs of impactors. For instance, two asteroids might collide, producing a small swarm of particles. Later their orbits would be modified so that they all would impact the Earth or Moon in a very short time, leading to a spike in the cratering record. It might take only 10--20 Myr for the contents of such a reservoir to hit a terrestrial planet.
His general conclusion, though, was that we are seeing the final stages of planet building, based on the lunar cratering record, particularly with the data from the Apollo landing sites.
How far back can we take the cratering record? The current accretion rate is estimated to be roughly 5.8 x 107 kg/yr. In contrast, the formation time of the Earth is thought to be something like 67 Myr. In order to assemble 1 Earth mass in this time would require a cratering rate some 1 billion times larger than what is observed presently.
Was the accretion "smooth" or "spiky"? Was the number of impacts per year changing only slowly or were there brief intervals of many impacts followed by intervals of essentially no impacts?
He plotted the number of craters having a given diameter. The crater diameter is then related to the impactor diameter. Of course, from the number of craters of a given size one can also estimate the frequency of such impacts. The plot has a very smooth shape, with many small impactors and relatively fewer large impactors. Indeed, it seems to show a power law with a scaling of d-1, where d is the diameter of the impactor. [That is, in comparing the frequency of impacts or the total number of impacts for impactors of different sizes, the frequency of impacts for two different sizes of impactors, d1 and d2, the ratio of the frequencies in is in the ratio d2/d1.
He also claimed that for the early cratering rate had to have been much higher. A K-T magnitude impact [such as the one that killed off the dinosaurs] happened about once every 100,000 yr. In the first 100 Myr, the cratering rate would suggest that there was a K-T magnitude event every year. This would have been a high enough cratering rate that the mantle could have been blown off and the Moon could have been formed.
He also pointed out that his graph for frequency of impact vs. diameter of impactor divides into a "uniformitarinism" portion, in which the events happen at a nearly constant rate, and a "catasrophasism" portion, in which only a few events happen during the age of the planet.
This leads to a "paradiegm" conflict. Lunar experts are heard to say that the cratering happened in a short period of time, well after the formation of the Moon. He points out that impacts can have an effect on the apparent age of rocks, by destroying older rocks. If there are enough impacts, few rocks would survive. That's what he claims the situation is. There are few rocks from the first 600 Myr, which has led to the claim that there was little cratering during the first 600 Myr. In fact the paucity of rocks older than 4 Gyr would be a natural consequence of a high cratering rate. Moreover, he pointed out that meteorite ages are not consistent with some kind of "cataclysmic" cratering period. Meteorite ages are smoothly distributed over the range 4--4.5 Gyr.
He concluded with a discussion of the effects of major impacts on both the Earth and Moon:
Hemisphere asymmetry of the Moon;
Lunar formation itself;
Magma ocean stirring;
Atmospheric erosion;
Accertion of oxidized materials;
Mantle melting;
Atmospheric generation;
Climate effects;
Frustration of life; and
stochastic differeneces between planets.
[I particularly like the idea of stochastic difference between planets. I've been thinking this way for a while. A single large impact near the end of the planetary formation time could result in two planets being quite different. It is good to see the idea put on more quantitative footing.]
Q: Talked about cratering record in terms of lunar exploration. It sounded as if he were defending the current NASA vision.
He discusses the availability of water. He claims that adsorption water is much more strongly bound to minerals than ice. He claims further that multiple adsorption layers are seen only a few centimeters below the Martian surface.
He summarized the surface layers of Mars. Above 1 mm, the soil can interchange with the atmosphere, and it is quite dry. Between 1 mm and 10 cm, the soil can be warmed temporarily and any water in it might be lost. Below 10 cm, the soil is thermally stable and should be wet.
He also posed the question of how much water is required to produce levels of the OH radical that might have an impact on biology? He suggests a carbon cycle in which bacteria play a role, but that would require some kind of aquaporine molecules that allow water in [to cross cell membranes?] during the night but then close off during the day to prevent water transport. [I believe he stated or the implication is that life on Earth may have such molecules.]
He described field trips to Utah, where there are large hematite deposits, potentially similiar to those on Mars. He described "nodules" ranging from less 1 mm to 5 cm in size containing large accumulation of hematite but that come in a wide variety of shapes, not just the nealy spherical of the blueberries on Mars.
He summarized a model in which these objects form during a high pressure flood that forces water into the rock, permeating it and bleaching iron from it.
He contrasted the geography of Utah and Meridani. At least in Utah [and Mars?] there are "knob" and "ring" structures possibly linked to percolation of water.
He showed formations in Utah that appear to have formed by the flow of water to lay down beds of rocks, followed by some kind of ocean to erode the rock. He suggested that the same process might have occurred in Meridani. [It does seem to require a lot of water, particularly for Mars. I recalled later that the western U.S. used to be a shallow sea, so at least part of this makes sense.]
He also presented some "anomalous" hematite accretions. He spectulated that these might represent biosignatures. The anomalies are that the hematite accretions are in the pore spaces of the rock rather than having been bonded to grains. Apparently there are also mineral differences between the anomalous hematite and "regular" hematite.
He summarized the finding by MOC of large neutron hydrogen signature on Mars. It imples water down to 1 m depths in the soil. It cannot be in the form of ice, because ice would sublimate in Martian conditions. He suggests that the water is in the form of a eutectic brine or clays/salt minerals with the water locked into them. The result would be a much higher water partial pressure below the surface[?].
He described zeolites, which are an aluminum-sulfur compound. There is a framework of Al and S, within which are water molecules and interstiticial cations. The result is that the water is held strongly within the compound. One example is clinoptilolite [I think]. Zeolites can hold lots of water under modest partial pressure, e.g., of order 10 mbar.
He then extrapolates to the Martian surface/subsurface. The temperature implies that the zeolites would be completely hydrated, but lots of the water might be bound so strongly that it would not be available for biology.
Q: How is this notion of lots of water consistent with the Christenssen results that found a largely dry planet?
He described Lake Vostok in Antartica. It was discovered only in 1994[!]. It is a lake covered by ice. Various ice cores have been drilled in the intervening decade. The ice crystals are quite pure, some of them reaching 10 cm in size.
The lake sits under 3.7--4 km of ice. At one end because of geothermal heat, the ice is melting (melt zone). At the other end, the geothermal heat source is weaker, and the lake water can re-freeze, accreting on the under surface of the ice sheet (accretion zone).
The cored ice has been divided into two types: Type I and II. He says that Type I ice shows sediments and is not very pure. [However, my notes also state that this is ice from the accretion region, which doesn't seem right. Seems more like Type II would be from the accretion zone of the lake.] Type II ice is quite clean. However, it is found only close to the lake surface. The least amount of ice covering is about 3.7 km, which sits above the accretion zone of the lake. Ice cores have drilled about 15 m into this ice, and it is estimated that there is about 85 m[?] left to go before the lake surface.
Both types of ice show very low oxygen content, some 100 to 1000 times lower than typical glacial ice. He also deduces a very low biomass. Based on a DNA analysis, the current estimate is less than 10 cells/ml for bacteria/archea and less than 0.1 cells/ml for fungi.
Looking for biology in the lake requires strict protocols to prevent contamination.
He also described a scenario in which the lake water could be superconcentrated in oxygen: Oxygen trapped in the ice in the melt zone is released into the lake, but then not re-incorporated into the ice in the accretion zone. That would leave the lake superconcentrated in oxygen with lots of oxidents.
Q: Seems to suggest that the cells counts are from Type I ice, from the upper parts of the ice sheet and not from Type II ice that is in direct contact with the lake.
Q: Could the forward protection (contamination) efforts actually be destroying cells in the ice, thereby leading to the low cell counts in the cores?
Summarized the NASA Astrobiology program. He illustrated the difficulty of the problem of finding life on other planets by showing a picture of some lichen on the underside of a rock in the Atacama desert. How could we find something similar on another planet?
He described studies of life on this planet as valuable but constrained. All life on this planet is related and uses the same information coding and transfer mechanisms. Questions he raised:
Life maintains structures?
Life interacts with the environment?
Signatures of life preserved?
How would we recognize life on another planet? Clues in the hunt for extrasolar life:
Creation of disequilibrium;
Creation of structures;
Existence with environment;
Multiple uses of relatively few molecules;
Preference for one chirality of molecules; and
Prediliction for light isotopes.
The NASA Astrobiology program has various ways to attack the problem including looking for biosignatures in rocks and lab experiments. Various programs are trying to understand the range of conditions (temperature, water level, energy amount) under which life can survive. Examples include work at the Rio Tinto, ice-covered lakes in Antartica, and life in the Atacama desert. Various programs also exist to support instrumental development and testing for future missions.
The focus on life includes
Where is the water?
Looking for structures (cells);
Looking for chemical gradients (or disequilibrium);
Testing for nuclei acids; and
[...]
There is a problem. If one considers the range of possible biosignatures and the range of possible abiotic processes, there is some overlap. This leads to ambiguity in some cases as to whether something results from biology or not. This is already a problem in some cases on the Earth. It will be even more difficult for other planets.
He mentioned that some lab experiments already suggest that different molecules can serve as the basis for life, but current remote sensing techniques would not detect them. If one does not assume that water is the solvent for life, this problem becomes even more difficult.
NASA has asked the National Research Council to evaluate the limits to "weird life" and the limits to organic life. He summarized a long list of questions in the charge to the NRC. I believe Meyer was the first to point out that we may found the limits already, in that portions of the Atacama desert appear too dry to be habitable by anything.
[Withdrawn?]
He began by describing the bombadier beetle, which utilizes a 25% solution of H2O2 to generate steam, even though H2O2 is typically assumed to be destructive to cells. He wants life on Mars to use antifreeze, be hygroscopic, and/or store oxygen somehow.
He suggests organisms could use an intracellular[!] fluid that is a mixture of H2O and H2O2. However, he points out that life would still need
UV screening;
Stablize the cell contents; and
Complex digestive system.
He pointed out that terrestrial life has had little incentive to develop such systems.
He concluded that sample-return missions might have problems with destroying their samples if the samples are stored at too high of a temperature or without an appropriate energy source. If there are such organisms, using H2O2, they could auto-oxidize.
He described the PHILAE experiment on the Rosetta lander. Rosetta has a focus on short-period comets.
He wants water at or near surface of Kuiper belt objects (KBOs). He showed spectra claiming that various spectral features indicated water on the surface in the past. The water would have resulted from radioactive heating of ice.
Rosetta carries PHILAE. (Philae was an obelisk that was essentially as useful in deciphering Egyptian hieroglyphics as was the Rosetta stone.) PHILAE [or Rosetta?] has the objective of
Determining composition of comet/landing site;
Measuring its physical properties;
Imaging; and
Cometary activity.
Among the various measurements will be one to measure the chirality of molecules.
The lander and orbiter can act together, for instance, the lander could evaporate something and then the orbiter determine what it sees.
Q: Questionner points out that ice would be present on KBOs [in present epoch, rather than liquid water?]
He described the concept of the Jupiter Icy Moons Orbiter (JIMO) experiment. The idea is to raise the bar of capabilities. He described an instrument to make use of a distributed aperture/sparse array, primarily for imaging. JIMO will have complicated trajectories between moons. It will spend, over 4 years, something like 26 months in transfer orbits, 14 months in in-spiral orbits, and 7 months in science orbits. He wants to take advantage of all of this time. They have a grant from NASA/HQ to study high capability instrument concept and technology.
Q: Are you going to be doing interferometry? [I asked this somewhat-loaded question because I think they do not quite appreciate the difficulties of doing sparse aperture imaging or how to interpret the results. Interferometric images are not as simple as those from a filled aperture, yet all of the images he showed were from filled aperture or simulated filled apertures.]
He summarized and speculated on planetary diversity. He pointed out that there is considerable diversity even within the solar system. Planetary mass objects range in mass from a lunar mass to Jupiter, a range of 1 million. There is a considerable difference between Earth and Venus, even though they have comparable masses.
He pointed out that the Terrestrial Planet Finder (TPF) and the Space Interferometry Mission (SIM) both seem to making the assumption that an Earth-mass planet located about 1 AU from it host star will be Earth-like. He also pointed out that water on Earth is actually underabundant relative to its cosmic abundance.
Planets exhibit remarkable diversity due to minor compounds, e.g., water and sulfur.
Planets in our solar system are underrepresent the range of diversity.
Known extrasolar planets are underrepresent the range of diversity.
The HZ concept may be antropocentric.
He distinguished between solid planets---terrestrial planets (Venus, Earth) and large icy satellites (Ganymede, Europa)---and fluid planets---gas giants (Jupiter, Saturn) and ice giants (Uranus, Neptune). He emphasized that the current sample of extrasolar planets is highly biased and essentially nothing is known about their composition.
Is there some kind of unifying diagram for planets, akin to the H-R diagram for stars? No, because planets have a large range of diversity, in part because of their composition and the potential role of minor elements. He emphasized that planets are complex [in contrast, stars are quite similar]. For planets, their distance from the host star plays a role, thermodynamically complex materials are important, and stochastic effects (e.g., massive impacts) may be important.
He described the potential importance of water on the Earth. It lubricates the astenosphere, which defines the plates, so water may be required for plate tectonics. In turn, plate tectonics allows for convection in the planetary interior, which can produce a magnetic field. Finally, all of these could be important for the emergence and subsequent survival of life.
He described the potential importance of sulfur on Mars. Whether an inner core formed may have been determined by the amount of sulfur. [Sulfur can be important in the crystallization of iron, I think.] Thus, the amount of sulfur on Mars may have affected whether it has a magnetic field.
What are the constraints on planetary diversity? There are strong constraints, such as whether a planet is dynamically stable in a potential orbit. There are moderate constraints, such as could such a planet be built from the cosmic abundance of elements. [I think he cited this as an example of why finding a Jupiter-mass iron planet would be difficult to imagine.] There are weak constraints, such as whether the formation mechanism for a hypothetical planet is conceivable. (Then he pointed out that there is no observation that some theorist cannot explain.)
He summarized the composition of planets. They are composed of ices (formed from C, O, and N) and dirt (Mg, Si, Fe).
He suggested a triangular diagram for organizing planets. At one vertex is gas, at the second vertex is ice, and at the third vertex is rock. A planet's location in this diagram (and therefore its classification) depends upon its composition. For instance, Jupiter and Saturn sit close to the gas vertex, Uranus and Neptune sit near the middle of the diagram, Earth and Venus sit near the rock vertex, and the Jovian icy satellites sit on the ice-rock line, about mid-way between the two.
He then suggested extending this triangle to form a prism-shaped object, with the third dimension being mass. Thus, one could locate in this diagram a planet with an Earth-like composition but with 1/10 of the Jupiter's mass (if such a planet actually could exist). He did predict, based on this diagram, that there will be "super-Ganymedes." These would be planets about half ice and half rock with about the mass of Earth.
Discussed habitability in terms of liquid water, sustained thermodynamic equilibrium, and "stable," in the sense of no killing events like massive asteroid impacts.
He also discussed three different kinds of oceans that a planet might have.
On its surface, like the Earth. He wonders if such an ocean might be unusual, that the Earth is in some sense "special."
Protected by a dense greenhouse atmosphere. He suggests a planet with a dense hydrogen atmosphere. A sufficient massive planet could retain a hydrogen atmosphere, under which might be an ocean.
An ice-protected ocean, in which the ice floats on the liquid water, akin to Europa.
He summarized the range of ways that water might possibly exist, from liquid water to frozen in soil to [...]. Also summarized the large icy satellites. He wonders if Ganymede has a natural structure for oceans, in which the interior is rock, on which sits high-pressure ice, on top of which there is an ocean, on top of which there is ice. [So an ocean sandwiched between two layers of ice.]
He points out that Galileo found 3 oceans in the Jovian moons. He predicts that oceans will be widespread. He predicts that Titan has oceans, with methane or ammonia serving as an antifreeze. He predicts that Triton has a subsurface ocean. The rocky core is warm, hotter than 1500 K from radioactive heating. A water/ammonia mixture could remain liquid. In particular, he points out that large craters seem not to be maintained on the surface of Triton, suggesting that the subsurface might be somewhat fluid. He even suggests that KBOs could have interior liquids, water and ammonia, that are warmed by the internal radioactivity.
He closed with interstellar planets. The surface temperature of such objects would be about 34 K. However, with a 1 kbar atmosphere, the surface temperature could be 300 K, and the planet could host an ocean. He points out that such a place might be a welcome waystation for interstellar travellers.
Q: To what extent will the interior of objects be mixed or stratified? Depends upon the formation. If via "hot" accretion, so that the accreted objects impact at high velocity, then one would expect stratified bodies. However, one could also imagine an ice-rock mixture that is not stratified, but later differentiated due to radioactive heating from the elements in the rocks. The result could be quite complicated internal structure.
Q: Interstellar planet characteristics? Depends upon planet and atmosphere [if any] mass.
He summarized plate tectonics. Plate tectonics
Stablizes CO2 content of atmosphere;
Continental breakup produces shoreline (habitat); and
Supports magnetic fields.
He summarized two different kinds of rock, and their potential impact on habitability. Granite is buoyant, relative to other rocks, so it floats on top. In turn, the erosion of mountains, which are largely granite, produces quartz rich sand, which is light in color. Volcanoes produce rocks like olivine, which in turn produce dark sand [like the black sand beaches in Hawai'i]. The penetration of light into these two kinds of sand is different; quartz-rich sand allows more light and more longer wavelength light.
Microbial life can live in translucent sands, into which radiation can pentrate. On the other hand, volcanic sands could support chemolithotrophs, if UV shielding had evolved. [I believe the implication here is that Martian sand is largely volcanic in origin and therefore quite dark.] Does this mean that there would be a microbial difference between a planet with plate tectonics and one without? Quite possibly, at least for land colonizers.
He also pointed out that plate tectonics has not been constant over time. The amount of crust on the Earth, and therefore the stuff that could participate in plate tectonics, has risen over time.
Are planets around M stars habitable? M stars are more abundant, and they have long lifetimes. However, they tend to be "active" [in the sense of producing flares] and often produce copious extreme UV radiation.
Extreme UV radiation can heat and evaporate an atmosphere. This is a potential problem not only for planets around M-type stars, but the Sun's extreme UV flux was higher in the past as well.
Carbon dioxide is an effective coolant of an atmosphere. Does this mean that the early Earth's atmosphere was high in CO2?
For M-type stars, previous studies have suggested that the atmosphere of a planet would collapse if the planet is tidally locked. In general, it is thought that a planet becomes tidally locked if its orbital semi-major axis is less than about 0.1 AU, although the details depend upon the stellar type, planetary mass, etc.
He describes a number of problems if the planet is tidally locked. Stellar activity is higher for younger stars, so tidally-locked planets would bear a heavier brunt of the activity. Also, it is not clear that a magnetic field could be produced. So the magnetosphere would probably be small, providing little shielding to the atmosphere. Finally, a coronal mass ejection, for instance as a result of the stellar activity, could compress a magnetosphere further and hasten the blow off of the atmosphere.
He distinguishes between the pre-requisites for life and for complex life. He is interested in the Galactic HZ.
The Universe needs to cool to the point at which radiation and matter have different temperatures. [Fortunately, that happened relatively quickly in our Universe.]
He suggests that there must be some minimum amount of "metals" (in the astronomical sense) to form a terrestrial planet. On the other hand, there is a clear correlation between the metallicity of stars and their likelihood of hosting a "hot Jupiter." So one can develop a "probability function" for terrestrial planet survival as a function of metallicity: At low metallicity, it is difficult to form terrestrial planets because there just isn't enough material, while, at high metallicity, the migration of the giant planet destroys the terrestrial planet.
He also refers to an analysis that the typical age of terrestrial planet is about 1.8 Gyr older than the Earth. [This analysis is either by him or Mario Livio, I think.]
He then compares metallicity, which has increased over time due to stellar nucleosynthesis, and the supernova (SNe) rate in the Galaxy, which increases toward the center. He finds a region over which terrestrial planets could form and survive and not be too affected by SNe. Perhaps not coincidentally, this region includes the Sun's orbit about the Galactic center. [If I recall correctly, his estimate of the Galactic HZ is that it includes no more than about 10--30% of the stars in the Galaxy and is an annulus about 7 to 9 kpc from the Galactic center.]
She describes the carbon distribution in the Murchison meteorite. About 70--80% is in insoluable macromolecules while 10--20% is in soluable compounds.
She points out that Earth organic [biogenic] compounds are severely depleted in 13C. [Organisms preferentially process the slightly lighter 12C isotope.] In interstellar space, the isotope ratio becomes much more equal.
She argues that the isotope ratios in interstellar space reflect abiotic chemistry. [I don't understand this. I recall thinking, Isn't this obvious?] Of course, there can be a variety of reaction pathways to form molecules in interstellar space.
She also seems to want delivery of amino acids from interstellar space to Earth for the development of life.
She summarized the search for life on extrasolar planets. She described the search as
Are there Earth-like planets? [Of course the planets around PSR B1257+12 indicate that the answer to this question is, Yes.]
Are they common?
Do they harbor life?
She stressed that this search is limited to global signatures. There is no hope [for the forseeable future] of being able to search for subsurface signatures on extrasolar planets. Thus, the emphasis is on global signatures, preferably with a signature that can be attributed unambiguously to life. She illustrated this vividly by showing the Voyager "family portrait" that shows how the Earth looks from the edge of our own solar system. [a pale blue dot]
She listed a number of potential biosignatures from the Earth, again stressing [rightly, I think] that astronomers are limited to strong, broad, global signatures.
Oxygen (and ozone);
The red spectral edge, due to chlorophyll in plants and bacteria;
Methane from methagens, though this signature may be too small to be seen; and
Other animal or anthropogenic signatures, but these are almost certainly too small to be seen.
For extrasolar planets, the emphasis will be on disequilibrium chemistry. [My notes also contain mention of "different solvents" and "giant planet atmospheres," but I'm not sure I remember what I meant.]
Over the next 15 years, the focus will be on
Oxygen and ozone. These are thought to be reliable indicators of life, in part because they are short-lived in an atmosphere (less than 1 million years) unless replenished continuously. However, she also raised the possibility of false positives [such as the idea of fully ice covered planet as mentioned earlier].
Methane. Currently this is a weak signature for the Earth, but maybe it was stronger in the past? However, could there be abiotic sources for it or is a false positive easier to get?
Water.
Red, vegetation edge. Chlorophyll produces a strong absorption band shortward of 0.7 microns.
She then summarized how this would be done. Direct detction of a planet is tough. One has to separate spatially the star and the planet and reduce the glare from the star by a factor of 1 million to 1 billion, depending upon wavelength. She described recent work on shaped mirrors designed to produce point-spread functions that have nulls in desirable places. This would reduce the star glare considerably in the nulls and make the detection of a planet possible.
She also described how transiting planets [HD 209458] could be used to detect planetary atmospheres.
She summarized the Galileo fly-by of Earth and Earthshine experiments. These are being used to try to understand how Earth would appear if viewed as an extrasolar planet, e.g., its spectrum or possible variation due to its rotation.
She also discussed false positives. Potential false positives include [the already mentioned] possibility that oxygen abundance in an atmosphere might not reflect life but processes such as an ice covered planet or an ocean boiling off. She also wondered if the red edge might be mimiced by some kind of mineral signature?
Q: Lichens do not produce a red edge.
Using a 2-body approximation for a star and planet in a planetary system, one can obtain an expression for the stellar insolation of the planet. For a gray albedo planet, one can solve for the equilibrium temperature. She asserts that this is a reasonable starting point.
She describes changing the eccentricity and obliquity of a hypothetical planet's orbit. She illustrated the temperature swings for a planet in an orbit with an eccentricity of 0.4. As for obliquity, for low values, the planet does not really have seasons.
She is working on the virtual planetary laboratory [of which more later].
She described atmospheric modeling using a 1-dimensional radiative transfer code. She has made model BD atmospheres and tried to test them against various observations. She has also made hot Jupiter spectra as a function of stellar type. In the latter case, depending upon the incident flux, one can have various lines either in emission or absorption. [Due to expansion of the atmosphere?]
He described Earthshine observations. He stressed that a large fraction of the scattered light can come from a relatively small fraction of the surface area. For instance at quadrature, 50% of the light comres from 5% of the Earth's surface area.
Earthshine itself is the light that reflects off the Earth, then reflects off the dark side of the Moon [note dark not far side!], and then returns to Earth. [It can be seen with the naked eye and is what allows one to see the dark side during the waxing or waning Moon.] Earthshine was first explained by da Vinci around 1506. In 1912 Arcichovsky suggested that one might observe to study the Earth.
Earthshine observations are technically challenging. One has to calibrate for the contribution of the Moon and Sun to the light; the dynamic range is large, for reference the difference between the Sun- and Earth-lit sides of the Moon can be 100,000 [which emphasizes the extraordinary dynamic range of the human eye]; sky subtraction; scattered light in the telescope; tracking the Moon [which most professional telescopes are not set up to do]; changing air mass; ....
He described an Earthshine experiment. They viewed the Moon when the primary part of the Earth illuminating was the Amazon, and then later when the primary part was the Pacific. They saw strong water and oxygen spectral signatures. Interestingly, the water features were weaker when the Pacific was illuminating the Moon. They saw the red edge from Amazonia at about 10% amplitude.
He suggested that the right way to do this kind of experiment would be from a South Pole station, from which one could get lots of observing time. At one time of the year, the Moon does not set.
He stressed that while the results were consistent with expectation, they were also not quite fully understood. [It wasn't clear to me that one would pick out the red edge unless one really knew already that it was present. I sort of got the impression that he also was not overly impressed with their detection of it.]
Q: What's the time scale over which the TPF will determine a spectrum of an extrasolar planet? Might it be longer than the rotation period of planet? He suggested that it might be as short as a few hours.
She is involved in the Virtual Planetary Laboratory (VPL), an effort to construct a virtual planet. She described some of the initial efforts, VPL-lite.
VPL has various "modules." She focussed on the three interlocking modules of
Host star spectrum;
Climate model; and
Radiative transfer.
She was specifically interested in how the Earth would have appeared at different times in its past. She considered modern, Proterozic, and Archean. Also, how might the modern Earth look if it were orbiting other stars. For instance, orbiting an F-type star, the higher UV flux might mean more ozone, but it also heats up the stratosphere and makes the ozone less detectable.
What about detecting ozone for the Earth orbiting an M-type planet? The ozone signature may disappear [presumably because of lower UV flux], even for oxygen levels at the modern value, but N2O might become detectable.
She concludes that oxygen is probably detectable to 1/100 of the present atmospheric level (PAL), and ozone is probably detectable down to 1/1000 for F, G, and K stars. M-type stars are more problematic.
Interestingly, the Proterozic may be the most detectable epoch in the Earth's past.
Is intel contingent or convergent?
One understands life by studying fossils and extant life to determine characteristics. Can one study fossils and extant intel to determine characteristics? What are the rules to intel?
Her work focusses on using lineage splits as different "experiments." For instance, the ancestral lines of humans and dolphins split about 100 Myr ago. This can be viewed as a 100 Myr experiment on large brains.
Some rules have been identified already. All processing systems (brains) use electrical (ionic) and chemical signalling, primarily Na and K. Brains are made of specialized cells, neurons. Brain size seems to be correlated with functional properties of the brain. In mammals, brain architecture is scalable. There is a correlation between brain size and complexity and the amount of social complexity. Finally the largest brain sizes seem to be correlated with tool use, both in vertebrates and invertebrates.
The questions she posed are, Is intel a biological certainty? Are the scaling principles for mammal brains in some sense universal or they limited just to mammals? Does intel of a species increase with time? Could intel species have appeared sooner?
The approach is to study the origin and evolution of brains in cetaceans (dolpins and whales). In studying brains, the EQ has been defined as the ratio of the brain size of a species to the brain size of a typical species with the same body mass. For reference, the great apes have EQ ~ 3 meaning that their brains are about 3 times too massive compared to other mammals of comparable body mass. Dolphins have an EQ ~ 5, and humans have EQ ~ 7. Cetaceans have both an EQ not too much smaller than humans, and the physical size of their brains is fairly similar to that of humans.
She points out that brain size of organims does increase with time but that this is simply passive diffusion. [In other words, there is a minimum size of a brain. In the extreme, one might say that the minimum brain size is one cell. Since the first animals were only a single cell or a few cells, it is possible for evolution to produce more complicated brains but not less complicated.] More importantly, do more intel species replace less intel species?[!]
She described a study of brain size involving 62 species of cetaceans, composed of 143 modern and 75 fossil specimens. [She emphasized that none of the modern specimens were killed for the purpose of the study, but they were found dead of natural causes.] They estimated brain volume and body weight, using CT imaging to estimate these quantities for the fossil species. Are there any mean differences over time? Are there any directional changes over time? [I.e., more intel or less intel?]
Results:
About 35 Myr ago, in the Oligence, there was a large jump in EQ as archacoceti gave rise to odontoceti (toothed whales).
About 15 Myr there was an increase in EQ for the specific species [or family?] delphinoidea [which contains modern dolphins].
Since the emergence of odontoceti, there has been no net increase in EQ in this group.
Conclusions: There is no trend of overall increasing intel.
She then described an on-going research program to expand this study and to try to identify patterns of evolution and breaks. For instance are there functional architecture or information processing principles?
Q: In her talk she showed a plot in which the range of EQ of odontoceti increased over time. Could this have been due to having more specimens to study the more recent epochs? She said that they did take subsets of the data in order to try to compenstate for this effect. She also pointed out that the Oligence was a time of ocean cooling, and therefore stressing the oceanic mammals. Could this have anything to do with it?
Q: Niche replacement?
[A talk on this research program had been given at Bioastronomy 2002, but at that time the work had just started.]
[He admitted that the subject of his talk had diverged a bit from his original title.] He argues that a large moon is required for intel.
The Moon stablizes the Earth's orbital obliquity, and he assumes that a variable obliquity would prevent the emergence of intel. He then summarized various simulations of the effect of planetary obliquity.
The rate of precession for the Earth is 50" per year. Various planets impose a forcing rate on top of this, the most dominant of which is Saturn which imposes a forcing rate of 26" per year. Because the natural rate is larger than the forcing from Saturn, the Earth's precession is stable.
He then tried different masses and angular momenta for the Earth-Moon system. He found that a large Moon is not required to stablize the precession rate as it is almost always larger than the forced rate. However, he also claims that the Earth-Moon system is just on the edge of stablity.
Moreover, a large moon also implies a slow rotation. Is a low rotation necessary for the emergence of intel? He cited several reasons why he thinks so: It minimizes Coriolis forces, it minimizes temperature variations, it minimizes seasonal variations, and it prevents a runaway greenhouse gas condensation.
He predicts that most extrasolar planet systems should have precession rates larger than 26" per year.
He summarized human evolution. The split between the hominind and chimpanzee/bonobo lineage occurred about 7 Myr ago. Genus Homo appeared about 2--2.5 Myr ago. Modern humans appeared about 160 kyr ago. A major advance in technology and culture occurred about 80 kyr ago. He discussed H. neanderthalensis briefly, as it possessed a larger brain, had culture, and was capable of speech. In defense of the last point, he argued that the shape of the hyoid bone [around the larynx?] was consistent with them having the capability of speech. He brought up the issue of whether Neandertals went extinct or bred with modern humans, and if they went extinct, why? The shift to agriculture occurred in 6 different areas between about 10 and 5 kyr ago, with cities and writing and record keeping being developed over the past 2--5 kyr. Writing was developed independently only four times.
He then went on to argue that we now have a space heritage and that certain space sites, at the very least Apollo 11, deserved to be preserved.
She compared the search for extraterrestrial life (SETI) and artificial intel (AI) studies. Both make the assumption that the human brain is not the only place where intel can reside.
Many early instincts about AI were wrong. It was thought that games like chess would be difficult for machines to learn while translation would be easy. In fact, it has turned out that chess is easy for machines but translation of languages is extremely tough. Translation appears to require full understanding of language and the underlying intel.
In another example, based on her own thesis research, it used to be thought that computers couldn't understand humor. Witness Data, the character from Star Trek: The Next Generation, who can engage in all kinds of highly complex movements but does not understand even simple jokes. In contrast it is easy, perhaps distressingly so, for computers to produce puns and "your mama" jokes. [At dinner one night, she shared some of these. The only one, unfortunately, that I can remember is, What do you call a beverage for a Martian alcoholic? An aleien (as in "ale"-ien). Yes, that was produced by a computer, and, yes, groan! :) ]
She summarized the Turing test. In a sense it is quite similar to SETI. In some respects both are flawed.
The test is quite strong. Many humans would fail it.
It is highly specific to humans.
It has distorted research. There has been a lot of focus on passing the Turing test.
There is no gradient in the test, it is all black and white. One either passes it or fails.
What are intel behaviors?
Adoption of new behavior on individual time scales, which includes both simple learning as well as adoption of new technology.
Communication or symbol use between members of group. Here, one needs to distinguish calls vs. language and communication over both time and distance.
Demonstration of simulative ability, or problem solving or reasoning about the behavior of others.
She confessed [at least partially tongue-in-cheek] that she wondered if brains were like peacock tails, i.e., they were sexually selected. [At lunch one day, one of the women present asked the obvious question, So would that mean that men's brains were "better" than women's brains? to much laughter. I don't quite remember her answer, but I think it was along the lines that she didn't take the idea all that seriously.]
She summarized some research in which they are trying to evolve a genetic algorithm to solve mazes.
She closed with a discussion of how to detect intel over distances? There are three possibilities: Communication, technology, or modification of the environment.
[I had the privilege of going to dinner one night with Lori Marino and Kim Binsted. Kim described an interesting phenomenon. She sometimes goes swimming in an area that is not too far from a dolphin pen. She says that she has occasionally gotten this creepy feeling that somebody's been watching her, even though there's nobody, at least no other human, around. She wondered if somehow the dolphin sonar might be affecting her. Lori said that it was quite possible. Lori has a fair amount of experience with dolphins and said that, if close to one, and it "buzzes" you with its sonar, you can feel it. Lori also said that pregnant women in a pool with dolphin are often "pinged" quite extensively by the dolphin.]
He described progess toward establishing the far side of the Moon as a radio quiet zone for SETI and for radio astronomy in general. The chronology of this proposal extends back at least to 1984 when Jean Heidmann proposed an observatory on the far side. He suggested explicitly Saha Crater. By 1996 this had led to a Lunar Farside Study sub-committee [though I'm not quite sure under the auspices of what organization] and a study. In 1998 the basic idea was sketched in a COSPAR meeting. However, in 2000 Heidmann died. Maccone took over the leadership of the sub-committee. In 2001 there was a meeting in JPL, and in 2003 the study was finalized.
The radio quiet zone on the Moon is actually a cone extending beyond the Moon's surface. This cone is the region for which the Moon shields radio emission from the Earth and satellites orbiting it.
The initial proposal was to use Saha Crater. However, it turns out that it may be illuminated already by terrestrial transmitters. During the course of the study, a second crater was identified, Daedulus Crater. This crater lies at 179 deg. east longitude, 5.5 deg. south latitude, and is 80 km in diameter. Thus, it is almost exactly in the middle of the Moon's radio quiet zone.
He described the 5 Earth-Moon Lagrange points. One potential problem with the idea of a lunar farside observatory is that it requires the L2 point [which is located on the far side of the Moon and on the line joining the Earth and Moon] be left alone. Any satellites placed there would illuminate the far side of the Moon. Another potential problem is that, during various parts of the Moon's orbit, the far side of the Moon could be illuminated by spacecraft in the Sun-Earth L points. For instance, SOHO [at the Sun-Earth L1 point] may be illuminating the far side already. Any deployment of a space station, a la the L5 society's proposal, would also be problematic. He suggested that one could orbit some kind of "space shield" near the Earth-Moon L2 point to shield at least it from the far side of the Moon.
He summarized various SETI programs. To date there have been 101 published surveys, ranging from 350 MHz to gamma-rays, and utilizing targetted, piggyback (commensal), and data mining approaches to searching. He summarized existing sky surveys and targetted searches, with an emphasis on Project Phoenix. The SETI Institute held a workshop a few years ago, the product of which was a book SETI 2020 laying out a strategy for SETI programs over the next 20 years. SETI 2020 called for a dedicated radio telescope array, originally called the 1 hT [for 1 hectacre telescope]; optical SETI (OSETI), and omni-directional SETI.
He summarized OSETI. It has at least two components. With existing technology, we could shine a Helios-like laser into a Keck telescope and outshine the Sun for 1 nanosecond. Thus, OSETI looks for short pulses in the optical or infrared. The difficulty is that OSETI assumes that any potential aliens are altruistic, because their targetting requirements---in order to make sure that the laser beam hits the Earth---are quite severe. In effect, OSETI assumes, for the most part, that the aliens already know that we are here. One potential twist on OSETI that does not require that the aliens know we are here, though, is the search for anomalous spectral lines toward stars.
The current sensitivity limits for radio SETI programs is 10-24 W/m2 in a bandwidth of 100 MHz over the entire sky. The SETI Institute's Project Phoenix has achieved a sensitivity of 10-25 W/m2 in a bandwidth of 2 GHz toward 1000 stars. This latter sensitivity limit corresponds to a 100 kW transmitter feeding a 100-m dish at a distance of 100 light years. The combined coverage of the OSETI programs corresponds to several thousand stars [though he did not quote a sensitivity limit].
Looking toward the future, he described the Harvard OSETI sky survey program. He mentioned a commensal search using the VERITAS Cherenkov detectors for a sky survey. [I presume this would mean using their detectors for an OSETI program, not for a program searching for high-energy gamma rays from an ET civ.] On the radio side, the long term program is an omnidirectional sky survey (OSS), however, this requires 1016 ops (computational operations per second) to process, which is currently unobtainable. He projects that it will take 15 years of growth in computational power, a la Moore's Law, before OSS will really be possible.
Summarizing the near future, the SERENDIP program will be returning to Arecibo to utilize the ALFA multi-beam system and thereby search the sky even faster. The original notion of the 1 hT has evolved into the SETI Institute's Allen Telescope Array (ATA). The ultimate goal is to have an array of 350 telescopes, each of 6.1 m diameter. They have not yet raised all of the funding for that, but they do have money for and are beginning construction of the first 32 telescopes in the array.
He showed a figure comparing the amount of sky searched vs. the rate at which the sky is being searched for different estimates of the number of ET civs. in the Galaxy. For an optimist, like Carl Sagan, one might estimate that there are of order 1 million ET civs. in the Galaxy. In that case one has to search roughly 100,000 stars to have a good hope of finding one, and, at the current search rate, it is projected to be until 2015 before this many systems will be searched. Drake himself estimates that there might be as many as 10,000 ET civs., which would require searching until about 2030[?]. A skeptic might estimate that there are only 100 ET civs., in which case we would not search enough stars until around 2050[?] to have a good chance of detecting one.
Q: In response to a question about the detectability of Earth, Drake sounded a pessimistic note. Satellite TV providers have become extremely adept at making efficient use of their power. For instance, he showed an image of the transmission power pattern for a U.S. satellite TV provider. They have shaped their beam so that its shape is a rough approximation of the shape of the U.S. The result is that very little power is broadcast into space for detection by any potential ET civs.
He advocates a stance of transmitting. He described a scheme of potentially using pulsars either as beacons or to define optimal search regions.
He described the Harvard OSETI program. In general, OSETI has few backgrounds [particularly in comparison to the radio]. The pulses are not dispersed, receiver gains can be made quite high, etc. They are conducting coordinated observations between Harvard/Smithsonian [Massachusetts] and Princeton [New Jersey]. Their timing precision is 0.1 microseconds. The simultaneous observations are designed to cut down on false alarms.
Their total observation time amounts to about 2400 hours, they've covered 6176 stars, and they found an rate of 0.47 "events"/hr. An "event" is when their photodetector is triggered. However, they've also been able to identify various systematic effects, such as a high humidity can result in spontaneous discharge within the photodetectors, and appear as false pulse of emission from a star. Removing times when they are likely to have been affected by these systematic effects, they have 1700 hours of observation time, on 4730 stars, for a rate of 0.16 events/hr.
They've conducted a Monte Carlo simulation of their observations. Their Monte Carlo simulations suggest that their observations are consistent with a constant background of occasional false alarms. They do have a few remaining events, but even these they think are probably due to systematic effects. Most importantly, there are no coincidences between the Harvard/Smithsonian and Princeton systems.
Based on the number of stars observed, they estimate that no more than about 1 star in 1000--10,000 hosts an ET civ. transmitting optical pulses.
He summarized the 6 different SETI programs being conducted at Berkeley, 3 in the radio, 2 in the visible, and 1 in the infrared.
SERENDIP uses the Arecibo telescope in a commensal mode to search 168 Mchannels, each 1 Hz wide. (He credited Jill Tarter with developing the name SERENDIP.) They've now conducted 1018 trials [for which each trial is a combination of pointing direction on the sky, frequency channel, and time]. He showed a newspaper article that summarized an earlier SERENDIP program as having conducted a lot of "fruitless" trials and joked that their trials continue to be "fruitless."
They have found a number of potential detections, what appears to be a signal in the same sky position, at the same sky position with the same profile. However, reobservations have not yet confirmed any of these.
He described the SETI@home program. The rate of participation is such that about 1200 CPU-years of processing are donated every day. In total there have been 1.9 Myr of processing donated. [I believe he called this the largest distributed computing project in the world.] In a typical developed country, the rate of participation amounts to about 1% of the country's population.
He summarized a number of the unintended consequences of SETI@home including people writing SETI haiku and people selling SETI@home work units on Ebay. He noted that each work unit that a person processes is associated with that person, so that if they ever do find ET, they will know on whose computer it was found. He pointed out that many people process work units, so even if one is found to contain a Nobel Prize winning discovery, one's prize winnings will be only about 20 cents [though of course I'm sure he knows that the Nobel Prize is never shared among more than 3 people].
SETI@home has spawned the open source BOINC program as well as a number of other distributed computing projects.
They will be starting the AstroPulse program to look for short radio pulses, as short as 0.4 microseconds, with absolute dispersion measures less than 100 pc/cm3.
Berkely is also involved in an OSETI program on the Lick telescope.
They have recently begun a search for Dyson spheres by looking for "older" stars with excess infrared emission.
He claims lots of "spin offs" from their work [though I didn't note what he meant by spin off].
He predicted that by 2030 it would be possible to do all-sky surveys using 1 million beams [which presumably means it would also be possible to process the data by then]. He also described archiving the data, which amount to something like 50 TB accumulated over 8 years.
[Dan's talk was widely agreed to be one of, if not, the most humorous in the entire meeting.]
She pointed out that the early Sun may have been more active. If so, it would have produced more X-rays than it does today as well their spectra would have been harder. Moreover, the atmosphere might have provided less shielding. Could clays have helped provide shielding for early life?
She described a series of laboratory experiments on DNA from Bacillus subtilis. They investigated it when it was both free as well as adsorbed on clay. In the latter case, the DNA ends up being more tightly wound. They exposed these DNA samples to irradiation levels equivalent to about 8 mon. of exposure for the Sun during an activity minimum or about 16 min. during a flare.
She defined a quantity Ftf which is the ratio of transformed cells after irradiation to the total number of cells. She showed that the effects of X-ray irradiation become important near levels of 1000 erg of exposure energy for free DNA, but clay adsorbed DNA shows little effect. However, the attenuation length of X-rays is quite small, X-rays probably would not penetrate most of their free DNA sample. Rather it is secondary UV photons, produced when the X-rays hit the sample, that are doing most of the damage to the cells.
She described a weird clay solution in which it is fairly transparent, but the DNA configuration is more compact so that the DNA is protected.
She speculated that clays could have helped protect the initial building blocks of life.
She defined a "habstar" as a star that has a habitable zone within which a terrestrial-mass planet can be dynamically stable over an evolutionary timescale. The star has to be of sufficient metallicity that terrestrial-mass planets can form. She pointed out that "evolutionary timescale" can mean different things, e.g., for the development of oxygen in the atmosphere (which might be detected by the TPF) or for a transmitting civ. to arise (which might be detected by SETI). On Earth, these two events were separated by 2 billion years. She has used the Hipparcos catalog to select potential habstars.
He described the use of a near-IR spectrograph on a 10.4-meter telescope [one of the VLTs?]. They have been using it to study the star GJ 569, which they've found consists of a double brown dwarf system orbiting GJ 569A. The ultimate goal is to try to search for terrestrial-mass planets around M-, L-, and T-type dwarfs.
He summarized the various ways one might detect planets including the Doppler effect [which has been used to find most of the current crop of planets], microlensing, astrometry, transits, and direct communication [SETI]. He then focussed on the Kepler mission, which will be a spacecraft to search for transiting planets. He emphasized that detecting transists is tough, as the decrease in light provided by a terrestrial planet crossing in front of a main-sequence star is extraordinarily small. The current Kepler catalog consists of 30 million stars, of which 170,000 are considered the "best" targets.
He described microlensing searches for planets. He pointed out that most of the other current planetary search techniques are at sensitivity levels about 10--100 worse than what is needed to detect a terrestrial-mass planet. Microlensing searches can detect planets that are at 1 AU distances from their host star. Microlensing suffers from the difficulty that the observations are not repeatable and the typical detected planet will be far[!] away.
Q: Is it possible to detect the reflected light from planets? Kepler might manage this.
Q: Effect of resonances from giant planets? These might make large regions of a planetary system unstable.
Q: Serendipity?! A number of people emphasized the need to consider the unexpected and look in places we might not otherwise expect to find terrestrial-mass planets.
[Unfortunately, I either missed some of these talks or took poor notes. I intentially did not take notes during Simon Conway Morris' summary talk. It was well done and quite comprehensive, though. He continued to stress a point he had made at the Bioastronomy 2002 meeting: The potential importance of convergent evolution. I had the privilege of sitting next to him on the plane from Reykjavik to London. He has, as he admits, the opinion that convergent evolution is a strong possibility in any ET life, perhaps even to the point that ET life would also use DNA as an encoding mechanism.]