Venus vs Titan: which is more likely to support life?

[magnemoe]

7 minutes ago, Steel said:

You're misunderstanding the Fermi Paradox. It's not just about whether or not there is life, but why we don't see more of it if it exists.

One of the main solutions is to posit a "great filter" (as mentioned earlier by K^2) which is a point in the evolution of life where the vast majority of life forms that come into being don't get past. If we find life on Titan, we at least know that the great filter isn't simple getting life started in the first place, which means that its more likely that the great filter is ahead of us. 

There's a waitbutwhy article that's really good if you want to read more about the great filter 

I understand, core is: why don't we see sign of high level alien civilizations? 
However life with Titan biochemistry would be very unlikely to result in an technical civilization as it would be low energy and slow.
Yes it would show that life is common, but not especially more high energy versions. It would be an very interesting find anyway.

 Life on the ice moons might be independent from Earth life, looking at the biochemistry would show that. 
Hard to get from Earth / mars to Jupiter or Saturn then land on an ice moon without getting vaporized then getting below the ice. 
Getting the other way would be easier, one major issue is that the ice moons might well lack the conditions for starting life even if earth microbes could survive there. 

As for the grand filter, its probably many, photosynthesis might be a big one, intelligence probably far larger. 

[Steel]

1 minute ago, magnemoe said:

I understand, core is: why don't we see sign of high level alien civilizations? 
However life with Titan biochemistry would be very unlikely to result in an technical civilization as it would be low energy and slow.
Yes it would show that life is common, but not especially more high energy versions. It would be an very interesting find anyway.

 Life on the ice moons might be independent from Earth life, looking at the biochemistry would show that. 
Hard to get from Earth / mars to Jupiter or Saturn then land on an ice moon without getting vaporized then getting below the ice. 
Getting the other way would be easier, one major issue is that the ice moons might well lack the conditions for starting life even if earth microbes could survive there. 

As for the grand filter, its probably many, photosynthesis might be a big one, intelligence probably far larger. 

Exactly, but what K^2 was saying (or at least what I interpreted) was that the discovery of any life in our solar system changes our view on the Fermi Paradox, because it eliminates one of the biggest historical "great filter points". Thus, it means that the "great filter" is more likely to be ahead of us, which is bad news for us as a species.

[Diche Bach]

I'd say it is a misconception of their being "one great filter." There are likely scores, even hundreds of them. As @Kryten pointed out above, glycine != nucleic acid (either RNA or DNA) though if glycine can form/exist it does suggest other complex organics such as nucleic acids might also be able to form exist in extraterrestrial contexts.

I'm no biochemist, but I'd suppose that even just getting to one of those to states: (a) an amino acid like glycine; (b) a nucleic acid like RNA or DNA, probably involves dozens or scores of "Great Filters." But as @Hypercosmic has pointed out, any sufficient conception of "life" is a lot more "filtered" than that. Even the simplest "life" probably involves hundreds of additional "Great Filters," and at that point all we have is a microbe of some sort . . . not exactly what "Fermi Paradox" is about, vis a vis, advanced alien Civilizations.

Going from microbe to prokaryotic ecosystem may well involve a mere handful or an enormous number of "Great Filters" and then we have the leap to "eurkaryotic" (or something analagous) organization.

Finding microbes proves NOTHING about Fermi. It doesn't even really prove anything except "Ah found microbes in 'space.' Well, now what does this mean about how organic systems have arisen in the range of contexts that this specific context might represent?" which still doesn't necessarily prove anything about the evolution of ecosystems. I'd agree with @magnemoe on this point: a planet with oxygen rich atmosphere and which is otherwise in a Goldilocks zone of some sort (and with Goldilocks characteristics) and perhaps other indicators of organisms capable of photosynthesis would be the minimum I'd consider to be "tentative proof of extraterrestrial life" (using life as the clunky shorthand for "ecosystems capable of evolving complex ecosystems and thus capable of potentially hosting the evolution of species with advanced intelligence") and I'd still insist on that word "proof" being clarified as tentative. Until we've got a probe in orbit of the place, else the sorts of remote sensing tech that can achieve comparable measurements and can get even more unequivocal evidence (physical samples are always the best) we cannot be certain.

As far as the pragmatics of "proving/disproving" Fermi, I think that is a straw man. It is only pragmatic in the event a rival extraterrestrial species is either on par with us or behind us somewhat. If they are in fact far advanced, we are at their mercy and they will either prove to be enigmatic, friendly, or genocidal, and there is not much we will be able to do about it. If they are on par or slightly behind us, then detecting and beginning proactive preparations for contact becomes pragmatic.

Edited September 26, 2016 by Diche Bach
clarification of clunky shorthand "life"

[Steel]

18 minutes ago, Diche Bach said:

...

Finding microbes proves NOTHING about Fermi. It doesn't even really prove anything except "Ah found microbes in 'space.' Well, now what does this mean about how organic systems have arisen in the range of contexts that this specific context might represent?" which still doesn't necessarily prove anything about the evolution of ecosystems. I'd agree with @magnemoe on this point: a planet with oxygen rich atmosphere and which is otherwise in a Goldilocks zone of some sort (and with Goldilocks characteristics) and perhaps other indicators of organisms capable of photosynthesis would be the minimum I'd consider to be "tentative proof of extraterrestrial life" (using life as the clunky shorthand for "ecosystems capable of evolving complex ecosystems and thus capable of potentially hosting the evolution of species with advanced intelligence) and I'd still insist on that word "proof" being clarified as tentative. Until we've got a probe in orbit of the place, else the sorts of remote sensing tech that can achieve comparable measurements and can get even more unequivocal evidence (physical samples are always the best) we cannot be certain.

...

I'd argue very much contrary to that.

If the we found life elsewhere and it could be said with reasonable certainty that it and we didn't have some common source, then the statistics suggest that life (maybe only up to microbial level but who knows) should be fairly abundant - if it occurs at least twice in the same solar system from different sources, then it's likely that it would be happening in many other solar systems.

The question then becomes about why, if there should be a lot of microbial life in the universe, why have we seen no signs of higher intelligence, hence the "great filter".

[Diche Bach]

My simple take is: extraterrestrial microbes, even abundant ones that are common on many bodies, does not prove that eurkaryotes are abundant or common.

The abundance/commonality of eukartyoes would not prove the abundance/commonality of 'ecosystems' or whatever an honest to God expert on the stuff would identify as the "next level" that would (stochastically speaking) tend to get "filtered."

The abundance/commonality of ecosystems would not prove the abundance/commonality of 'advanced ecosystems' etc. . . .

In short: there are many, many "leaps" to be filtered between microbes in space and something like the Cambrian explosion having occurred anywhere except Earth.

[magnemoe]

3 minutes ago, Diche Bach said:

I'd say it is a misconception of their being "one great filter." There are likely scores, even hundreds of them. As @Kryten pointed out above, glycine != nucleic acid (either RNA or DNA) though if glycine can form/exist it does suggest other complex organics such as nucleic acids might also be able to form exist in extraterrestrial contexts.

I'm no biochemist, but I'd suppose that even just getting to one of those to states: (a) an amino acid like glycine; (b) a nucleic acid like RNA or DNA, probably involves dozens or scores of "Great Filters." But as @Hypercosmic has pointed out, any sufficient conception of "life" is a lot more "filtered" than that. Even the simplest "life" probably involves hundreds of additional "Great Filters," and at that point all we have is a microbe of some sort . . . not exactly what "Fermi Paradox" is about, vis a vis, advanced alien Civilizations.

Going from microbe to prokaryotic ecosystem may well involve a mere handful or an enormous number of "Great Filters" and then we have the leap to "eurkaryotic" (or something analagous) organization.

Finding microbes proves NOTHING about Fermi. It doesn't even really prove anything except "Ah found microbes in 'space.' Well, now what does this mean about how organic systems have arisen in the range of contexts that this specific context might represent?" which still doesn't necessarily prove anything about the evolution of ecosystems. I'd agree with @magnemoe on this point: a planet with oxygen rich atmosphere and which is otherwise in a Goldilocks zone of some sort (and with Goldilocks characteristics) and perhaps other indicators of organisms capable of photosynthesis would be the minimum I'd consider to be "tentative proof of extraterrestrial life" and I'd still insist on that word "proof" being clarified as tentative. Until we've got a probe in orbit of the place, else the sorts of remote sensing tech that can achieve comparable measurements and can get even more unequivocal evidence (physical samples are always the best) we cannot be certain.

As far as the pragmatics of "proving/disproving" Fermi, I think that is a straw man. It is only pragmatic in the event a rival extraterrestrial species is either on par with us or behind us somewhat. If they are in fact far advanced, we are at their mercy and they will either prove to be enigmatic, friendly, or genocidal, and there is not much we will be able to do about it. If they are on par or slightly behind us, then detecting and beginning proactive preparations for contact becomes pragmatic.

Yes eurkaryotic might have happened once and after an 1.5 billion years, might be the main filter. Looks like the jump from single cells to multi celled and up to more advanced creatures had happened multiple times and is easier. 
Intelligence is another one who has only happened once, yes many mammals and birds are pretty smart so it might well have come other intelligent species. Even intelligence might not be enough, you have to be smart enough and very social. 

A bit doubtful to a primary filter in the future outside the matrix is more fun and space travel to expensive, if Mars or Venus was habitable we might well have colonized them by now or be very close, some aliens would be so lucky having an second planet, it would both give an gigantic boost to space exploration and get them clear of most catastrophic future filters. We are probably not that many hundred years away from an asteroid civilization adding another insurance  

[Diche Bach]

Heh, heh, just stumbled on this recent thing: Meet Luca, the Ancestor of All Living Things

. . . of course, that isn't the ACTUAL Luca . . . she died a long time ago I reckon.

But that is probably what she looked like  . . . they think (I guess) . . .

[Green Baron]

Yes, if there were traces of life on other bodies the question "where are they" would receive a new meaning. That would prove that life(tm) could emerge multiple times in a solar system, not in every solar system but in those that offer the right environment, the filters apply later.

Mars is within the zone where liquid water could exist (lwz), aka "habitable" Zone but i hate the word because it only describes one of many constraints. A lot of asteroids are in the "habitable" zone. Venus is probably too close (see earth) and life in a cloud layer is too much science fiction for my poor brain :-). Titan, if it was in another system, would not be considered in that zone when viewed from earth.

I miss Mars here, because of two reasons: First i doubt that other bodies than Mars or nearby asteroids are within our reach (for a probe complicated enough to search for life(tm)) in the next decades. Second if looking for habitable planets in other systems a planet like Mars would be easier detectable than a moon like Titan, thus if we knew if Mars once had microbes we could project that knowledge easier into other systems. The moons of the gas giants just have more constraints to take into account, like tidal forces and radiation from the planet. Or, in other words, we already have enough difficulties identifying the lwz around another star, identifying one around another gasgiant just complicates things.

So i hope somebody goes to Mars and takes a closer look.

[todofwar]

44 minutes ago, Green Baron said:

Yes, if there were traces of life on other bodies the question "where are they" would receive a new meaning. That would prove that life(tm) could emerge multiple times in a solar system, not in every solar system but in those that offer the right environment, the filters apply later.

Mars is within the zone where liquid water could exist (lwz), aka "habitable" Zone but i hate the word because it only describes one of many constraints. A lot of asteroids are in the "habitable" zone. Venus is probably too close (see earth) and life in a cloud layer is too much science fiction for my poor brain :-). Titan, if it was in another system, would not be considered in that zone when viewed from earth.

I miss Mars here, because of two reasons: First i doubt that other bodies than Mars or nearby asteroids are within our reach (for a probe complicated enough to search for life(tm)) in the next decades. Second if looking for habitable planets in other systems a planet like Mars would be easier detectable than a moon like Titan, thus if we knew if Mars once had microbes we could project that knowledge easier into other systems. The moons of the gas giants just have more constraints to take into account, like tidal forces and radiation from the planet. Or, in other words, we already have enough difficulties identifying the lwz around another star, identifying one around another gasgiant just complicates things.

So i hope somebody goes to Mars and takes a closer look.

Well I see Mars as being in a different category. I would paint the two match ups as Mars vs Europa and Venus vs Titan. Venus and Titan, in my mind, represent the extremes of what is possible to support life, possibly even outside of those extremes. Mars and Europa are closer to being really possible, though of course it's not confirmed. 

[Green Baron]

I see ... in this case i'm one of the Titans (Titanians ?)  :-)

 

[kiwi1960]

On 25/09/2016 at 7:14 AM, Diche Bach said:

Well, I hope we can agree that a "A comet with an icing of glycine [I'm a poet and didn't know it!] does not life mean." But it is rather fascinateeng.

I still would like to hear how the brightest minds in those research areas hypothesize how that stuff _got there_.

to answer you, I don't know, but I'll think about it and get back to you... k?

OH WAIT... you weren't actually referring to me when you said "the brightest minds..." ..... damn....

as you were. Nothing to see here, move along... its just an ego deflated Kiwi.... move along.... thank you....

 

[kerbiloid]

12 hours ago, todofwar said:

Venus and Titan, in my mind, represent the extremes of what is possible to support life, possibly even outside of those extremes. Mars and Europa are closer to being really possible, though of course it's not confirmed. 

I would swap Europa and Titan.

Venus, Io

Earth edit: Øŕþ

Titan

Mars

Europa, Enceladus

Edited September 27, 2016 by kerbiloid

[K^2]

20 hours ago, magnemoe said:

I don't see how Fermi paradox will be affected by life on Titan. Even if its life on it and even if the life type on Titan was common on Titan type planets.

Statistics and entropy. Given life on Earth, I can say with confidence that there is life on Earth. Given life on Earth and on Titan, I can construct a probability distribution that is very heavily slanted towards some form of life being present in nearly every star system. If it was otherwise, finding two planets with life in the same star system would be extremely unlikely. And the type of planet or life form is irrelevant. We just have to be able to exclude common origin via panspermia.

And no, this doesn't tell us that life on Titan-like worlds is likely. That would be true if all we had was a completely random star system and we found life on it on a Titan-like world. No, the crucial statistical quirk here is that there are two distinct origins for two distinct life forms in one star system. Rest is cold statistics.

Fermi Paradox is better viewed as proof by counterexample. (I'm simplifying a bit, but I don't want to get bogged down in details.) Suppose life is common in the universe. Suppose, it is natural for complex life to evolve from simple life. Suppose, complex life tends to evolve towards intelligence. Suppose, intelligent life tends to evolve into a space-faring civilization. Then we ought to have encountered some indications of one in our neighborhood. We have not, therefore, one of our assumptions is false. The condition preventing that assumption from being fulfilled is referred to as the Great Filter. The big question is, which one is it?

We are pretty confident about simple life to complex given a good environment, and there are going to be a decent number of planets with the right environment based on latest data. Finding life on Titan would also cross out the first one. So either intelligent life isn't common, or civilizations don't make it very far past discovering radio and space flight. If it's former, we might not have anything to worry about. If it's the later, we are heading for some catastrophe more likely than not.

Right now, our best bet on great filter being behind us is if life is not all that common to begin with. That would mean Earth is special, either due to circumstance or by lucky draw. Life on Titan shoots it down, dramatically increasing the odds of great filter still being ahead. And that's something we really, really need to know.

[magnemoe]

54 minutes ago, K^2 said:

Statistics and entropy. Given life on Earth, I can say with confidence that there is life on Earth. Given life on Earth and on Titan, I can construct a probability distribution that is very heavily slanted towards some form of life being present in nearly every star system. If it was otherwise, finding two planets with life in the same star system would be extremely unlikely. And the type of planet or life form is irrelevant. We just have to be able to exclude common origin via panspermia.

And no, this doesn't tell us that life on Titan-like worlds is likely. That would be true if all we had was a completely random star system and we found life on it on a Titan-like world. No, the crucial statistical quirk here is that there are two distinct origins for two distinct life forms in one star system. Rest is cold statistics.

Fermi Paradox is better viewed as proof by counterexample. (I'm simplifying a bit, but I don't want to get bogged down in details.) Suppose life is common in the universe. Suppose, it is natural for complex life to evolve from simple life. Suppose, complex life tends to evolve towards intelligence. Suppose, intelligent life tends to evolve into a space-faring civilization. Then we ought to have encountered some indications of one in our neighborhood. We have not, therefore, one of our assumptions is false. The condition preventing that assumption from being fulfilled is referred to as the Great Filter. The big question is, which one is it?

We are pretty confident about simple life to complex given a good environment, and there are going to be a decent number of planets with the right environment based on latest data. Finding life on Titan would also cross out the first one. So either intelligent life isn't common, or civilizations don't make it very far past discovering radio and space flight. If it's former, we might not have anything to worry about. If it's the later, we are heading for some catastrophe more likely than not.

Right now, our best bet on great filter being behind us is if life is not all that common to begin with. That would mean Earth is special, either due to circumstance or by lucky draw. Life on Titan shoots it down, dramatically increasing the odds of great filter still being ahead. And that's something we really, really need to know.

Yes agree that life of Titan indicates life is more common, however ocean life on an ice moon unrelated to earth would be an better indicator as its the same overall life type using carbon and water. 
Using statistic with an low sample rate is lots of guessing however life started early on earth indicating its relatively easy. 
Not so long time to get photosynthesis either, it happened many times. 
Advanced cells or eurkaryotic took a 1.5 billion years, likely that this was hard and is an major filter.
Multi celled and more complex organisms also happened many times. 
Cambrian revolution, might also be an rare event, it might also be an result of an snowball earth ending and more oxygen required for larger animals. 
Looks like the next filter is intelligence or at least an class of animals who have an good chance for intelligence. 

Anyway, think exoplanet search is an better way to find answer to this question, number of earth like planets, the fraction of them with oxygen in atmosphere will answer how common life is. Next step would be harder but an 100 pixel image of an exoplanet would give lots of information about plant life on land, not sure if it would be easy to see difference on an algae layer and a forest however. 

[Matuchkin]

Here's a nice source.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664683/

There are some nice planetary and lunar analogies in this article, and good explanations of conditions at the time that life began on Earth.

[K^2]

18 hours ago, magnemoe said:

Yes agree that life of Titan indicates life is more common, however ocean life on an ice moon unrelated to earth would be an better indicator as its the same overall life type using carbon and water.

Different type is a much stronger indicator. Any life we find on Mars or in subsurface oceans of outer moons can have common origin with terrestrial life. We find rocks from Mars on Earth all the time. life could have easily first evolved there. Or it could have evolved on Earth and one of comet impacts would have spread it through Solar System. We've had life long enough for this to have happened several times over.

If life we find happens to have same origin as life on Earth, we are back to sample of one. No matter how rare life is in the universe, we are guaranteed to live in a star system that has life, because we are a life form. So the basic fact of finding life elsewhere in the Solar System tells us nothing. But if we can prove that it has evolved independently, then we can make a statement about how common life is likely to be in the universe. And while water-based life could still prove to be different enough that we could distinguish it as separate origin, even that would take decades of research to exclude a very early diversion. Methane-based life, however, could not have come from the same ancestor as water-based life. So finding life in surface lakes of Titan would automatically give us two distinct origins.

Not that I'm going to complain about discovery of any sort of life on any other body in this Solar System. It'd still be a great discovery and we are bound to learn much invaluable information. If I can stretch my earlier lottery analogy, finding life anywhere in the Solar System would be winning a lottery, but finding it on Titan would be getting the big jackpot.

[todofwar]

12 hours ago, K^2 said:

Different type is a much stronger indicator. Any life we find on Mars or in subsurface oceans of outer moons can have common origin with terrestrial life. We find rocks from Mars on Earth all the time. life could have easily first evolved there. Or it could have evolved on Earth and one of comet impacts would have spread it through Solar System. We've had life long enough for this to have happened several times over.

If life we find happens to have same origin as life on Earth, we are back to sample of one. No matter how rare life is in the universe, we are guaranteed to live in a star system that has life, because we are a life form. So the basic fact of finding life elsewhere in the Solar System tells us nothing. But if we can prove that it has evolved independently, then we can make a statement about how common life is likely to be in the universe. And while water-based life could still prove to be different enough that we could distinguish it as separate origin, even that would take decades of research to exclude a very early diversion. Methane-based life, however, could not have come from the same ancestor as water-based life. So finding life in surface lakes of Titan would automatically give us two distinct origins.

Not that I'm going to complain about discovery of any sort of life on any other body in this Solar System. It'd still be a great discovery and we are bound to learn much invaluable information. If I can stretch my earlier lottery analogy, finding life anywhere in the Solar System would be winning a lottery, but finding it on Titan would be getting the big jackpot.

On the other hand, if it can be shown that life = water with a higher confidence interval, then the presence of water goes from one of many criteria to the strongest indicator. Further, if we do prove that bacteria can survive in vacuum and enter another planet and seed that planet, that has implications for Fermi because suddenly life appearing on one planet might mean the whole galaxy becomes seeded eventually, but if that process is faster than random chance producing life on it's own than proximity to the mother planet might be the criteria for who gets intelligent life first.

[magnemoe]

17 hours ago, K^2 said:

Different type is a much stronger indicator. Any life we find on Mars or in subsurface oceans of outer moons can have common origin with terrestrial life. We find rocks from Mars on Earth all the time. life could have easily first evolved there. Or it could have evolved on Earth and one of comet impacts would have spread it through Solar System. We've had life long enough for this to have happened several times over.

If life we find happens to have same origin as life on Earth, we are back to sample of one. No matter how rare life is in the universe, we are guaranteed to live in a star system that has life, because we are a life form. So the basic fact of finding life elsewhere in the Solar System tells us nothing. But if we can prove that it has evolved independently, then we can make a statement about how common life is likely to be in the universe. And while water-based life could still prove to be different enough that we could distinguish it as separate origin, even that would take decades of research to exclude a very early diversion. Methane-based life, however, could not have come from the same ancestor as water-based life. So finding life in surface lakes of Titan would automatically give us two distinct origins.

Not that I'm going to complain about discovery of any sort of life on any other body in this Solar System. It'd still be a great discovery and we are bound to learn much invaluable information. If I can stretch my earlier lottery analogy, finding life anywhere in the Solar System would be winning a lottery, but finding it on Titan would be getting the big jackpot.

You have an point, one issue is that just detecting life on Titan might be hard, its low power and we don't know that we are looking for. 
Still think that better telescopes for finding and then looking for oxygen on exoplanets is better for answering this question. 

[Starman4308]

On 9/22/2016 at 4:37 AM, K^2 said:

Titan, by far. Methane is actually the best solvent there is for cryogenic temperatures. Reason we need polar solvents at Earth temperature ranges is because you need strong hydrogen bonds to make up organic machinery in cells at 300K. Anything weaker would be too unstable, so you couldn't have things like DNA, for example. But then to build out of blocks with such strong bonds, you need polar solvents like water.

On the other hand, at 90K of Titan, you don't want such strong bonds in your organics to begin with. Instead of polar bonds, you're looking at van der Waals forces. With weaker bonds, you want weaker solvent. Non-polars like liquid methane will do just fine. With a caveat, that this does greatly limit the range of available chemistry for building life with. But you kind of expect that at such low temperatures either way.

I don't know if conditions for life to being on Titan are there, nor do I know if it's possible for something to evolve there in time that conditions were right, given how slow everything is going to be at these temperatures. But Titan has conditions compatible with a form of life that uses methane for solvent and catabolizes acetylene for food. This is a lot more than I can say for Venus.

I will say more. While I don't think Titan is the likeliest place for us to find life in the Solar System, it is the most important place for us to check. As I explained above, it is possible for a form of life to exist there, and we have some very loose tangential evidence suggesting that something like consumption of acetylene by life forms or mineral process is taking place there. Could totally be a red herring, likely even. But if we find life on Titan, it would be the most important discovery human kind has made ever. Because if life exists on Titan, it is life that definitely doesn't share origin with Earth's life. And that puts two independently evolved life forms into one star system. Not only would we have to greatly expand what we consider to be a habitable region, but we'd also know that universe is absolutely full of different kinds of life. Whereas, if we find life on Mars or Europa, it wouldn't be nearly as exciting, since we still would have to exclude common origin and it doesn't do nearly as much to expand our definition of habitable. So while it could still point to life Out There, it's not half as great a discovery.

On the balance of how likely it is, vs how important it would be as a discovery, I would mark Titan as the most important celestial body for us to study this century.

You do realize protein folding is driven by hydrophobic effects, right? Most proteins will have their polar side chains exposed to solvent, with a hydrophobic core providing stability to the fold. The intra-chain hydrogen bonds, such as those characterizing alpha-helices and beta-sheets, is barely, if at all, more favorable than hydrogen bonding with water.

If there is life living in a methane environment, I'd expect it be invert that, and have hydrophilic, polar/charged cores to its macromolecules, with hydrophobic groups surface-exposed to the methane. The worst solvent for life would be something like a soap, which can dissolve across a very wide spectrum of hydrophilicities.

As to Venus: on the surface, that's a flat-out "no"; the temperatures there would rip any non-covalent interaction, and many covalent interactions, to shreds. Maybe in the clouds, but I'm not so sure about that one. At least on Titan, there is a condensed-phase substrate that won't slaughter any organism that comes across it.

Edited September 29, 2016 by Starman4308

[K^2]

5 hours ago, Starman4308 said:

You do realize protein folding is driven by hydrophobic effects, right? Most proteins will have their polar side chains exposed to solvent, with a hydrophobic core providing stability to the fold. The intra-chain hydrogen bonds, such as those characterizing alpha-helices and beta-sheets, is barely, if at all, more favorable than hydrogen bonding with water.

You do realize that proteins, and anything else that relies on hydrogen bonds, are going to be frozen solid at 90K, right? Fortunately, the only reason we need hydrogen bonds for our life is because weaker bonds can't withstand 300K. On Titan, they don't need to. If cryogenic life exists anywhere in the universe, its basic molecules aren't going to be proteins. They will be much simpler hydrocarbons with no functional groups that would result in strong polarization. The energy scale you are looking for at 90K is van der Waals interactions. There are a number of functional groups that would allow hydrocarbon chains to behave similar to proteins, but at much lower temperatures and with no polar bonds involved. The perfect solvent for these molecules is, indeed, methane.

There are limitations, certainly. Flexibility is much less of an issue for proteins at 300K. Getting hydrocarbon chains to fold at all at 90K is going to require a lot of compromises. That means, you are going to lose a lot of complexity. At the same time, I'm not expecting marvels of intracellular engineering like the kinesins or the ATP synthase. We are talking about the most basic life. Something that can metabolize acetylene to power self-replication and construction of the simplest of barriers between itself and the environment. That doesn't take nearly as complex of biomolecules as complex life requires. If it did, life would probably never be able to evolve in the first place.

I have no doubt that life on Titan is possible. Given unlimited time and resources, even with our understanding of biochemistry, we could engineer something that would qualify. The only question is whether it's capable of emerging naturally. Given much, much slower rates of all chemical processes and reduced variety of options that could possibly work, age of the universe might not be sufficient time for this to have happened anywhere. Then again, all other chemical barriers are lower, and variety of molecules isn't as high to begin with, so maybe it's not all that difficult. I have no idea. I'm pretty sure nobody else can say for certain as well. Given that Titan is practically in our backyard, on cosmic scale, we really ought to just check.

[todofwar]

3 hours ago, K^2 said:

You do realize that proteins, and anything else that relies on hydrogen bonds, are going to be frozen solid at 90K, right? Fortunately, the only reason we need hydrogen bonds for our life is because weaker bonds can't withstand 300K. On Titan, they don't need to. If cryogenic life exists anywhere in the universe, its basic molecules aren't going to be proteins. They will be much simpler hydrocarbons with no functional groups that would result in strong polarization. The energy scale you are looking for at 90K is van der Waals interactions. There are a number of functional groups that would allow hydrocarbon chains to behave similar to proteins, but at much lower temperatures and with no polar bonds involved. The perfect solvent for these molecules is, indeed, methane.

There are limitations, certainly. Flexibility is much less of an issue for proteins at 300K. Getting hydrocarbon chains to fold at all at 90K is going to require a lot of compromises. That means, you are going to lose a lot of complexity. At the same time, I'm not expecting marvels of intracellular engineering like the kinesins or the ATP synthase. We are talking about the most basic life. Something that can metabolize acetylene to power self-replication and construction of the simplest of barriers between itself and the environment. That doesn't take nearly as complex of biomolecules as complex life requires. If it did, life would probably never be able to evolve in the first place.

I have no doubt that life on Titan is possible. Given unlimited time and resources, even with our understanding of biochemistry, we could engineer something that would qualify. The only question is whether it's capable of emerging naturally. Given much, much slower rates of all chemical processes and reduced variety of options that could possibly work, age of the universe might not be sufficient time for this to have happened anywhere. Then again, all other chemical barriers are lower, and variety of molecules isn't as high to begin with, so maybe it's not all that difficult. I have no idea. I'm pretty sure nobody else can say for certain as well. Given that Titan is practically in our backyard, on cosmic scale, we really ought to just check.

I don't know, I think anything big ad a protein will have a hard time dissolving in methane, even polyethylene at comparable molecular weights won't dissolve in boiling hexane (which isn't that hot but much hotter than liquid methane). There has been talk of polycyanides that can act as photocatalysts, maybe they're just consuming the acetylene. If they convert some of it to cyanide, and that polymerizes to another active polycyanide chain, would that count as life? Serious question. 

You also highlight one of the reasons I set up this matchup. Earth chemistry is so varied because we have week and strong interactions and interplay between them. But on Venus you get only strong interactions, on titan only week interactions. Most biochemistry relies on covalent bonds top hold things together, but hydrogen bonds to direct and organize things. With only one or the other what do you get? 

[todofwar]

http://link.springer.com/article/10.1134/S0038094612010042

Half life 3 life on Venus confirmed!

[ProtoJeb21]

Even with those apparent "Venusian Scorpions", I still consider Titan a far better place for life. It has a liquid cycle, a protective atmosphere, is inside Saturn's magnetosphere, has liquids on its surface, and is geologically active. The basic things for a habitable planet (geologic activity, liquids, atmosphere, and magnetic protection) are right there! So, Titan may be cold to us, but chill isn't as hard to overcome as heat. Titan could have icy equivalents to Earth's deep-sea hydrothermal vents in its largest seas like Kraken Mare. Also, there are signs of something living on the moon. The Huygens probe found out that there was a mysterious decrease in the amount of hydrogen in Titan's lowest atmosphere. This went in line with astrobiologist Chris McKay's prediction of Titan-based life using hydrogen like we use oxygen. I say that Titan is the better potentially habitable world.

HOWEVER....

I don't rule out the chances for life on Venus. It seems possible that some bacteria species could've escaped into the planet's atmosphere when the rapid oceanic evaporation began. Bacteria have been shown to adapt to almost anything, so it's not far fetched to say that they could've learned to live in the clouds for the last 4 billion years.

[todofwar]

2 hours ago, ProtoJeb21 said:

Even with those apparent "Venusian Scorpions", I still consider Titan a far better place for life. 

I loved that paper for the level of detail they put into analyzing frames. Like someone picking out the taxonomy of Martian squirrels.

[kerbiloid]

15 hours ago, todofwar said:

Half life 3 life on Venus confirmed!

A big difference between these two: the latter is possible.