[X] My Assistant

[jaredGalen]

Thought this article title was a little over the top, the kind of one you would
expect to see followed by lots of exclamation marks.

Interesting article though.

"IF LIFE exists on Titan, Saturn's biggest moon, we could soon know about it - as long as it's the methane-spewing variety. The chemical signature of microbial life could be hidden in readings taken by the European Space Agency's Huygens probe when it landed on Titan in January."

http://www.newscientistspace.com/article.ns?id=dn7716

[exoplanet]

I quote JRheling:

"Consider that some of 2004's top ten scientific discoveries (as rated by AAAI) concerned the chemical properties of WATER. If we don't yet understand H2O inside and out, forget about predicting life given some alternative chemical basis.

To put a spotlight on the problem, consider that a water molecule essentially consists of 15 particles, and so a pair of water molecules involves up to 435 interactions. Create a computer model of those two water molecules, and you have a lot of math to juggle. Fine, that's tractable, but make it 100 water molecules, and forget about it (although, admittedly, you could make simplifying assumptions -- not all of those interactions will amount to much). So simulating a water nanodroplet is a big task. This just goes to say that "brute force" computation cannot be the bridge between molecular chemistry and a hypothetical new kind of biology. And if water still holds secrets, you can see that no more-burly kind of chemical theory is in hand yet."

Thank you for your post. It is conceivable that if we do not know all the properties of water . . . how in the heck do we know what the limitations of life is. I am by no means from the astrobiological mindset, however, I do believe that from what has been discovered both from Cassini and Hyugens . . . a more complex probe/rover would be a highly rewarding endeavor for both NASA and ESA.

I would love to begin some very heated discussions about the surface and atmospheric chemistry of Titan and the implications to the possibility of life pro and con. It is already being discussed in some important scientific journals and I would like to begin the discussion here as well (Also, I don't have the $ to subscribe or a nearby university to access most of the recently published articles).

[JRehling]

I quote JRheling:

Rehling, but lots of people like to move the H!

I would love to begin some very heated discussions about the surface and atmospheric chemistry of Titan and the implications to the possibility of life pro and con.  It is already being discussed in some important scientific journals and I would like to begin the discussion here as well (Also, I don't have the $ to subscribe or a nearby university to access most of the recently published articles).

A fascinating (and speculative) topic is the issue: Given a planet with appropriate conditions (for life as we know it, or LAWIK), what is the probability that life will actually arise? Internet posts and books can be found postulating (or arguing, or hoping) that the number is very close to 1.0. (Of course, the definition of "appropriate" is a wildcard!) If I had to make a guess this instant, I would say the opposite, something very close to 0.0. But some basic key facts are:

a) We have no unbiased data. We know of one case of biogenesis, but that data point stems from the same basic fact that we are here to make that observation! This is the anthropic principle at work.

We have a merely-kinda biased data point in that life on Earth seems to have arisen very quickly -- it didn't just dawdle around and then suddenly happen at some time in the middle of Earth's history. Or did it? It's not quite a solid fact when life could have arisen. And in any case, if life on Earth could have arisen at any old time, but it happened to arise, say, in the first 1% of the time that it possibly could have, that is merely a suggestive finding -- not proof. There was a 1% chance it would have done so anyway. In fact, more than 1%, because we wouldn't be here to talk about it if biogenesis of bacteria had happened only a million years ago.

c) It doesn't happen VERY fast. You can't throw the right nonbiological compounds in a bucket for an hour and get bacteria to evolve. It doesn't happen in days, or weeks, and probably not in centuries. But with a bigger bucket? A Pacific Ocean sized bucket, and a million years? What about a thimble and a trillion years?

Let's try this model: Given a quantity of soup, and a span of time, how great does the product of those two numbers have to be for life to arise? We might guess that given twice the bucket size, we could expect life in half the time. This model is valid if biogenesis consists of enthalpy's little fingers twirling organic molecules like Rubik's Cube, "trying" to create biology and succeeding when the correct sequence occurs by chance, which is inevitable given enough molecules in enough oceans over enough time.

Is that a correct model? Surely on some level, but tempered by modularity. Life did not arise when the molecules making up a raccoon or a pine tree randomly fell into place. The cell was an intermediary step from which natural selection could proceed, and surely there are subcellular intermediate steps as well. But still, something had to arise that crossed the natural-selection barrier. This process is not well understood.

To work with a simple model, I took the random-compilation model and assumed that biogenesis took place when M molecules were placed together in the right linear sequence. In other words, if biogenesis were the sorting through of M! (M factorial) permutations, until the right one were found. Then, for planet-like values of ocean-bucket volume and geological time, what is the probability of biogenesis as a function of M?

That's surely not literally accurate, but the mathematics were instructive. If M were 2, then biogenesis would take place in a thimble in a fraction of a second. If M were very very large, biogenesis would take place in very vast space and very vast time. The question is, how does the probability of biogenesis (some of the key values of Drake's Equation) vary as a function of M? We don't get to alter M, the laws of biochemistry have determined it, but it is still interesting to see how Drake's Equation might depend upon the inherent laws of the universe.

The answer is, the probability (Pl) of biogenesis on a planet given a few eons is very near 1.0 for low values of M, and then as M grows it very abruptly switches to near 0.0. The switchover happens somewhere around 55 (to cosmological standards of approximation, the exponent you'd use to express the number of molecules in an ocean times the number of molecule-manipulations you'd have in an eon).

This is so based on speculation that no conclusions can be drawn, but it seems quite reasonable to me that biogenesis is a freakishly rare event -- lacking a way to clean up all of my questionable assumptions, we still get a basic truth -- if the number of elements in the minimum requisite biosufficient "thing" is less than about 50, the galaxy will be full of life. If it's more than about 60, we may be totally alone -- not one stinking bacterium in all the galaxies anyplace farther away than Voyager 1!