Saturday, January 28, 2012

Comets, astrobiology, the origin of life

In Chandra Wickramasinghe's 2009 book, he mainly proposes comets as agents of transportation of panspermia cells. The prospect of billions of comets having had water for up to a million years, and larger, comet like objects even having permanent water, does lead him to believe they are also agents of the generation of the chiral precursors to life. He uses a lot of the most recent cometary findings to back up his case.

He doesn't go to the extent I have of thinking how far chemical evolution has gone in comets, whether an RNA world or DNA world could exist in a comet, and think why would it stop evolving? If it hadn't stopped, it may have got to a point where the proto-life in the comet may act in a way that may increase the chance of the "survival" of the comet, in the kind of attrition where comets are gradually getting absorbed into planets with hostile environments. Could actions by the proto life make it more likely for the comet to split up into two, where one of the fragments would be more likely to survive than if it hadn't split? Could chemical or biological action by the protolife make the outside of the comet black? Would that give the comets an alternative energy source for the middle of the comet to stay liquid (the original source being decay of Al 26 or otheer elements)? Could the emmission of particles from the gaps in the black exterior serve as ways to control the spin of the comet, or even course corrections (to avoid planets, or to get close enough for a gravity assist)? Could the emmission of particles get rid of unhelpful chemicals in a kind of metabolism?

In other words, if we can see evolution working in the environment on Earth that leads to eventual intelligent behaviour due to the needs of survival, why wouldn't this be the case for comets?

Principally, is there any evidence that the two most obvious features of life are plausibly existing for comets? That is, do they reproduce? Do they metabolise? Certainly, there is plenty of evidence that they "break up". How could we tell whether this is similar to a living cell breaking up, or a non-living rock breaking up? For metabolism, how could we tell whether the outgassing is making the outside more random and making the inside of the comet more ordered? Is it plausible that it is just outgassing a random selection of compounds that make up its interior? Could it be that it is metabolism regardless of whether the comet is a living thing?

The very high resolution images of Hale Bopp combined with ground observations of the spin and emission profile, may give us some ideas on splitting comets. The rate of rotation is not constant, and the axis of rotation is such that the two ends of the peanut shape may pull apart if it spins up to a fast enough speed. The change in rotation has been determined to be from the activity of the jets streaming out more in one direction than the other. From ground observations, the spin-up is more efficient than the spin-down. The conclusion is that the comet will eventually break up due to the centrifugal forces therein. It doesn't take much imagination to feel that it could be a rudimentary reproduction similar to amoebas.


Chris Fellows said...

I'm sorry I don't have more to say about comets. My thoughts are all fiction-oriented when they're not what they ought to be, which is work-focussed... :(

Marco said...

Fair enough. I assume you got my email? Let me know if you have any conventional chemistry that could make comets surfaces so black. We should make a prediction before the Rosetta lander lands on a comet in 2014. I predict that if it manages to get a sample without sinking, it will find the organics homochiral. I expect the black surface to be spongy, rather than rocky.

Chris Fellows said...

No, I didn't get your email that I can see.

The conventional chemistry in Wikipedia's comet nucleus article is good enough for me.

I predict that repeated cycles of degassing/surface ionisation alternating with cosmic ray bombardment at low temperatures will have left the surface composed of very high molecular weight material very enriched in carbon, iterating towards a limit state of carbon nanotubes oriented perpendicular to the surface.

I predict that if the Rosetta lander manages to get a sample without sinking, it will find the organics racemic and overhwelmingly polymeric, with little low molar mass material.

I agree that the black surface will be spongy/crumbly.

Marco said...

On Earth, long chain organics are almost exclusively associated with living organisms and human manufacture. This is not quite like metabolism, as living things tend to take up all of the available carbon, and (do you know?) if there is any reasonable random mixing of chemicals in a frozen environment, that would polymerize and concentrate the carbon? I am dubious that it would concentrate on the exterior, as an element, and not peel off when nearby chunks escape, and I am not prepared to accept that it must because it does. However, if long chain organics have a biological origin, are they usually chiral?

Would you accept the possibility of biological origin if the black organics had a high chirality?

Marco said...


4.       The phenomenon of optical activity in natural petroleum:  Evidence of an abiotic, high-pressure genesis.
          Perhaps for reason of its historical provenance in fermented wine, the phenomenon of optical activity in fluids was for some time believed to have some intrinsic connection with biological processes or materials.20, 21  Such error persisted until the phenomenon of optical activity was observed in material extracted from the interiors of meteorites;  some of which material had been believed previously to be uniquely of biotic origin.

Is this right? It is saying that chiral molecules must be abiotic because they existed on meteorites? Shouldn't they *prove* that there is no biota on parent asteroid bodies before they can use it to come to this conclusion?

Chris Fellows said...

I said high molar mass; I didn't say long chain. Stuff like I am postulating is found in, f'rinstance, soot.

Marco said...

I think I got it. Doing a bit more research, which you probably know all about, because I was thinking something more akin to tar. Apparently, petroleum is now assumed to have non-biological origin, despite its optical activity. Evidence of which is that meteorite petroleum-like compounds also have optical activity.

Marco said...

However, homochiral compounds of any carbon compound with high enantiomeric excess, will be harder to explain the same way as that of carbonaceous meteorites. Those compounds are said to have obtained their chirality through high pressure processes in very large asteroids.

Marco said...

Read that book on the origins of chirality, or I will lose faith with scientists in general, the way things are going. I desperately hope I'm missing something, but it appears scientists are making up facts to suit their theories on the origins of chirality, among other things.