NASA recently announced that they had discovered an amino acid, glycine, in a comet. This comes two years after the Stardust probe had flown by a comet's tail, collected dust in an aerogel bucket, and parachuted the bucket back to Earth for analysis.

The significance of this discovery, is that amino acids are the building blocks of proteins, and proteins are the workhorses of life. Did this discovery mean that comets have life?

That was the reason for the delay. The scientists wanted to be sure that this particular glycine came from the comet and not, say, from oily fingerprints left by the technicians who assembled the bucket. The first problem was that there was so very little of it. We're talking about less material than a fingerprint, merely the vapor from an impacting dust grain. So the team set up their lab and kept calibrating and testing until they felt they would be sensitive to even that small an amount. Then they carefully took samples of foil from around the site of a dust-grain impact (sort of like looking at the gunpowder stains around a bullet hole) and ran it through their mass spectrometer.

I have a special fondness for mass spectrometers, crediting them for snatching me away from solid-state physics and directing my career into space plasma physics. So I can appreciate the carefulness with which they carried their sample to the instrument, gently heating the surface while flowing noble gases or organic solvents over it and then delicately ionizing the molecules to avoid destroying the organics. It is a tour-de-force, demonstrating a proper reverence for the unique sample of comet dust that they had spent 100's of millions of dollars obtaining, and might never obtain again. And indeed, the isotope of Carbon-13 revealed the glycine to be not from Earth.

On the other hand, they might have spared themselves the anxiety because tons of cometary dust rain down on the earth every year, and when big enough chunks make it through the atmosphere to hit the ground, they are classified as carbonaceous chondritic meteorites.   Unfortunately, rain and water will dissolve these type of meteorites, so unless they are collected immediately, they will vanish. But by good fortune we have about a dozen of them over the past century that were collected immediately. And when we analyze them, they are chock full of glycine, as well as four other amino acids and even two nucleobases, the building blocks of DNA. And just like Stardust, these amino acids are made of extraterrestrial heavy carbon.

So yes, Stardust confirms what carbonaceous chondrites have been telling us, there is extra-terrestrial life.

We've known this for upwards of 40 years, but the two primary counter-arguments that it doesn't represent extraterrestrial life have been: (a) contamination; (b) non-biological origin.

Is it Contamination?
1) All amino acids are chiral, with Left-handed (L) and Right-handed (D) forms. All living organisms are only L-amino. Test-tube chemistry can make amino acids, but lacking a chiral catalyst, they generate equal amounts of L and D called a "racemic" mixture. Given that cosmic rays or heat can break/remake chemical bonds, an originally chiral amino acid will become racemic given enough time. Therefore determining whether cometary amino acids are L, D, or racemic will indicate their source.

Answer: they are noticeably non-racemic, with a bias toward L-amino showing that they are either very old life, and/or mixed with some non-biological racemic amino acids.

2) There are 20 amino acids in life, although many more in the test tube. Not all of them are equally stable, with half-lives from a few thousand years to a few million. As a consequence, dinosaur protein surviving 60 million years is considered a true miracle. But more significantly, the presence or absence of select amino acids can tell you how long it has been since a organism was alive. Think of it as C14 dating for proteins. What do comets show?

Answer: Comets are missing many of the complete 20 amino acids, consistent with a clock of 10-100 million years. This is also consistent with the racemization seen in point 1.

3) All life on Earth is recycling CO2 from the atmosphere. The oceans dissolve a lot of CO2 as well as recycle old carbonates, so they represent an older atmosphere. The two stable isotopes of carbon are C12 and C13. Because C13 in methane or CO2 makes it noticeably heavier, C13 settles out of the atmosphere more readily and eventually disappears from the life cycle. So all recent life shows an enhancement of C12 over C13, whose normalized ratio is called by mass spectroscopists "dell-13". Dell-13 for terrestrial organisms runs from -30 to 0, with plants near -30, people near -10, and marine organisms near 0 (which is how they caught Floyd Landis doping on artificial testosterone). What do comets show?

Dell-13 for amino acids recovered from meteorites are above +35, very heavy carbon. Nothing even remotely terrestrial has those numbers. See the articles in this book.

At the Astrobiology conference this year (SPIE publication coming in about 1 month), two necleobases (A&T?) found in carbonaceous chondrites were described (original discovery published in 1970's) whose dell-13 was also +35.

Conclusion: from (1) we know that these amino acids were made by living organisms. From (3) we know that when they were alive they munched on "heavy" carbon not found in the Earth ecosystem. From (2)+(3) we know that they were alive a long, long time ago. Therefore it is not consistent with recent Earth contamination, nor with ancient abiotic contamination, but only with ancient life.

But is it a Comet?

I suppose there is a sliver of an argument that carbonaceous chondrites aren't comets, but if they aren't then we have lots more problems. Consider:

a) They arrived like all meteorites, from extraterrestrial material hitting the earth

b) The parent bodies of most meteorites are known, from stony to nickel-iron asteroids, by matching their reflectance signature. The parent bodies of carbonaceous chondrites match the spectra from the 3 or 4 comet flybys, as well as some recent Hubble measurements. (Dark black objects are hard to see, especially when surrounded by a glowing ball of evaporating gasses, hence the very recent measurements.)

c) An asteroid that has water on it, must produce a tail if it is within the orbit of Mars. Solar system objects with tails have historically been called comets.

d) The composition of carbonaceous chondrites is heavily proto-solar, undifferentiated, lots of "dusty" supernova remnants. If it is not a comet, then its origin would be very mysterious.

So that's why 99% of the meteorite community thinks that they are extinct comets. Of course, we can't rule out that they might be refuse from flying saucers too, but you can see why such explanations raise more questions than they answer.

But did NASA's Stardust return cometary silicates lacking water?

Another name for hydrated silicates is concrete. If you took a piece of concrete from your sidewalk, turned a propane torch on it for a few minutes until it glowed, it would dehydrate the silicates and resemble the powdered cement you began with when you mixed it up in the first place. The silicates collected by Stardust were travelling some 6.1 km/s relative to the aerogel collector. If all that kinetic energy were turned into heat, the kinetic temperature would be about 125,000K, where the boiling point of silicates is perhaps 3000K, so the sand would completely vaporize.

Therefore the entire mission hinged on the ability of aerogels to stop a dust grain without thermalizing it, either by ablation or elastic collisions etc. Despite careful calibrations, every "track" left by a dust grain in the returned aerogels shows a "ballooning" in the middle, where the grain exploded, evidently from heating. So rather than saying it was a surprise not to find hydrated silicates, I would rather ask whether one should be surprised to find silicates at all. 

But Stardust was calibrated before launch, and showed that hydrated silicates from a carbonaceous chondrite would survive capture in the aerogels. Doesn't their absence prove that comets aren't carbonaceous chondrites?

Yes, they did do hypervelocity studies, but not having actual comet to test, they used proxies. Here's what I think is the difference between their proxies  (which included carbonaceous chondrites!) and a comet. When dust is lifted off the comet later to be collected by Stardust, did it consist of hydrated "mud" or anhydrous dust? Did it come from a water geyser or a vapor jet? To answer that, we have to discuss the life history of comets.

Carbonaceous chondrites are the end product of many, many trips around the Sun, where a comet melts and sublimates many times, effectively creating a well-mixed, well-hydrated precipitate or agglomerate that subsequently gets baked solid when all the liquid water boils off, leaving behind mostly hydrated minerals still stable at the relatively cool temperatures of the comet (some 400K according to Halley's armada). That's why the team expected hydrated minerals, because that is what is found in chondrites.

Young comets that have just arrived in the solar system, however, are big, fluffy and dusty, since the ice has never melted, the dust has come straight from a stellar furnace and is therefore anyhdrous, and sublimation pressure of evaporation drives anhydrous grains out of the fluffy comet's weak gravity well. This is the original "Whipple" model, which was widely accepted before the first visit to comet Halley.

All this changes when a comet melts, forms concrete, and then collects water. The jets coming off a melted comet are then water jets, or geysers, though limited to regions near the equator. Eventually, erosion changes the stability of the spinning comet, and it does a spin flip putting the "apple core" shape into a tumbling mode, or a prolate comet.

Adolescent or prolate comets have some melted spots (near the equator) and some dusty spots (near the poles). I think the ESA-ROSETTA mission to comet C-G is going to find an adolescent comet. My paper suggests that liquid water acts as a speed governor in a comet, keeping it right at the rotation rate that generates a Rayleigh-Taylor instability. If it spins faster, it melts more water, the water moves to the equator, and slows it down. But as a comet ages, it loses more water and becomes hollow. This means that the moment of angular inertia changes, so in effect the R-T "speed limit" keeps dropping. (The math is in the paper). So the age of comet can be determined from its spin rate.

Comet Wild was definitely up there in age, with some 90% of its water gone (based on density measurements and spin rate), with temperature maps showing nearly a constant 273K surface temperature, e.g. melting point of ice. All this suggests that we should expect hydrated minerals, or mud in its outgassing.

But when a comet is nearly hollow, the source of the outgassing is no longer the pockets of liquid water near the equator, where centrifugal force concentrates them, but the huge reservoir of gas in the interior bursting out of the thin spot at the pole. This can be seen by the stability of the comet jets in inertial space, which was certainly true of comet Borelly. This suggests that rather than water geysers, a comet of Wild's age will end its life with a gas geyser powered by unmelted dusty ice in its core, more similar to the first pass of a long-period, Oort-cloud comet.

And that means the dust scooped up by Stardust will likely contain clusters of anhydrous crystals held together by ice that evaporate within days or hours of being ejected from the comet. More mysterious is why the grains of fosterite "sand" were in the comet in the first place, which suggest that it may have scooped up terrestrial dirt in the inner solar system. I haven't tried to calculate it, but perhaps there is more cometary recycling of dirt than I had thought.

The Stardust team calibrated with hydrated silicates, so we know they can survive impact, so where are they? And how do you know that carbonaceous chondrites are comets? Maybe they are leftover planetesimals and the amino acids are primordial?

And just as concrete is a mixture of sand and hydrated silicates, it doesn't surprise me that the small, hydrated crystals (look at a microphotograph of concrete) would have exploded, leaving behind the fosterite filler. I think the observations are consistent with the hypothesis that the collection method evaporated the hydrated crystals, and that carbonaceous chondrites, while cometary in origin, have been processed differently than the material outgassed by a comet.

And while my description of the life-cycle of a comet is undoubtedly speculative, it is nonetheless based on observations both before and after the spacecraft-flyby era, as well as being consistent with the physics of rotating objects.

Whether carbonaceous chondrites are primordial planetesimals, water-bearing asteroids, or amorphous achondritic accretions, they would all produce tails when orbiting the Sun inside the orbit of Mars. And historically, anything with a tail was called a comet. You can call it lots of other things as well, but as far as I understand, it doesn't stop it from being a comet.

Finally, amino acids might have been in the primordial stuff that made the solar system, just as crude oil might have been part of stuff that constructed the earth (Tommy Gold's hypothesis), but amino acids would not have survived 5 billion years to the present, except perhaps buried under a foot of ice in the Oort cloud, because cosmic rays, sunlight and heat would have destroyed it. In fact, as I mentioned in a previous post, many of the 20 amino acids are missing in comets for precisely this reason, giving a "clock" of between 10-100 million years for their origin. And while this rules out recent contamination, it doesn't support primordial origin either.

So once again, I do not attribute ancient life to comets lightly, nor do I propose it for ideological reasons, but because there aren't any other theories that work. If any of your alternate explanations are better, then they have to explain: the missing amino-acid racemization, the missing amino acids, the missing non-biological amino acids, the presence of nucleobases, the dell-13 enhancements of both amino acids and nucleobases, the fossilized blue-green algae, the missing nitrogen of the fossils, the water-soluble nature of the fossilization; not to mention the older telescopic evidences: the cometary source of cyanogen, the outbursts of distant comets, the color of comet surfaces, the prolate shape of comets, the phylosilicates ejected by the Deep Impact probe, and the presence of sand grains in comets, to name a few. The data is overwhelming, and the only hypothesis that brings all these surprising observations together is that of life on comets.

Could any of these signatures be "front-loaded", primordial organic materials placed there by God for their subsequent use on Earth?

While I believe in front-loading, I don't think you and I agree on the mechanism. As I wrote on my website a month ago, I think front-loading is a term invented by Laplacian determinists, to explain how Newton's equation of motion, F=ma, can be based on initial conditions x0 and v0. Since QM has destroyed that Newtonian precision, and chaos theory destroyed the remaining hold-outs for initial conditions, it seems that now "algorithmic" front loading is proposed instead: where the universe is a computing machine executing some "boot sequence" program stored as information, e.g., the machine keeps updating its state based on a stored data base so it doesn't need phenomenal precision. Based on my understanding of the Turing problem of feedback, I have argued that even algorithmic front-loading is impossible. That is, there is no place to store the program separately from the computer, and hence "strong" Turing feedback prohibits a deterministic outcome.

Nevertheless, as you may have read in my "Cometary Biosphere" paper, I think the Earth shows a "bootstrap" progression of information and life just like a laptop starting Windows. So how can it be possible to believe in both a bootstrap Earth, and the impossibility of bootstrapping?

The resolution, I believe, lies in the nature of information.

When attempting to solve a problem on a balloon-born astronomy platform, where Harvard U had spent a million dollars on a star-camera pointing system, but failed to deliver a usable product, I concluded that the information in the starfield existed in both the CCD-image, and in its Fourier transform. Harvard researchers failed to lock onto the starfield because they neglected the information in the Fourier transform. This led me to an essay on Fourier transforms as an analogue of eternity and as another way to view global information.

Applying this insight to our bootstrap problem, the universe as created by God is like a computing machine playing back the boot-prom-program that does not itself exist locally in the machine, but globally, around the machine. That is, the hologram of the universe holds the information that drives the components of the universe toward complexity. You can also think of this as the QM entanglement of all the wavefunctions from the creation of the universe. Since something that is ubiquitous or global cannot be material, we are looking at information being "spirit". So in effect, we solve the Turing dilemma by getting rid of feedback between the parts, by getting rid of the parts, by making everything global.

Well such a view is unfortunately very close to Tipler's "The Physics of Immortality" and its quasi-Hegelian emphasis on "world spirit", or Teilhard de Chardin's "Omega Point", etc. But that is because Tipler gives the Fourier transform the primacy, whereas materialism gives the space-time locality the primacy. I would argue that neither is primary, but both are important.

This is akin to the Chalcedonian solution that Christ is 100% human and 100% divine. Such a view, of course, is nonsense, since something cannot be itself and its opposite without violating basic principles of logic. However Church Fathers at Chalcedon didn't derive its validity from dualism, or from denial of logic, but from an affirmation of the Trinity.

So the reason Tipler is wrong, the reason Teilhard is wrong, the reason Hegel is wrong, is that they deny the Trinity. The reason we can hold the world and the spirit in creative tension, is because there is a third thing that "is before all things (material), and in him all things hold together (spirit)." (Colossians) or even better, "the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe (material) by the word of his power (spirit)." (Hebrews).

We may be able to unravel the material of the universe, and even detect the spirit that holds it together, but the information lies in the word who created it.