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Colin Robinson
2013-Jun-10, 10:39 PM
How important is Titan in the search for answers or clues about life in the universe?

I think Titan is very important, for the following two reasons:

1.Because it might have life: life that is chemically very different to life on Earth. This would mean a second abiogenesis, with huge implications for the prevalence of life in the universe.

2.Because it might not have life. In which case it will tell us something about how complex organic molecules behave and interact in a planet-sized environment without organisms. Again, the implications are huge.

G.Gaylord Simpson compared search for life beyond Earth to a gamble at long odds.

If Titan is seen only as a place to look for life, then yes, sending a lander there would be a gamble. However, if Titan is considered as a place to look for life and to look for clues about the origin of life, then it is not a gamble at all.

ASTRO BOY
2013-Jun-10, 10:50 PM
How important is Titan in the search for answers or clues about life in the universe?

I think Titan is very important, for the following two reasons:

1.Because it might have life: life that is chemically very different to life on Earth. This would mean a second abiogenesis, with huge implications for the prevalence of life in the universe.

2.Because it might not have life. In which case it will tell us something about how complex organic molecules behave and interact in a planet-sized environment without organisms. Again, the implications are huge.

G.Gaylord Simpson compared search for life beyond Earth to a gamble at long odds.

If Titan is seen only as a place to look for life, then yes, sending a lander there would be a gamble. However, if Titan is considered as a place to look for life and to look for clues about the origin of life, then it is not a gamble at all.



While we have any doubt at all about the existence of life beyond Earth, any gamble to answer the question once and for all, is important for human kind and will and must be undertaken eventually...

Selfsim
2013-Jun-11, 03:50 AM
How important is Titan in the search for answers or clues about life in the universe?
...
If Titan is seen only as a place to look for life, then yes, sending a lander there would be a gamble. However, if Titan is considered as a place to look for life and to look for clues about the origin of life, then it is not a gamble at all.The search for life in the universe, is secondary to the fundamental drive to gain scientific knowledge. Without such a driver, the search for life elsewhere, would remain where it was in the dark ages.

IMO, the search for life is not necessary in a strategy for achieving the broader focused goal. In fact it undermines it .. because its motives are largely philosophical, and are thus a gamble.

You assume a lander might be necessary for life detection and origin clues(?).. I notice one possible end to the Cassini mission, is for the spacecraft to aerobrake in Titan's atmosphere, and enter into long-term orbit around it. This would enable study of the atmospheric characteristics at lower altitudes. The study of PAHs might therefore be achievable without the need for a lander (as an eg). Landers also localise the searchable terrain, as opposed to enabling the global perspective achievable from orbit .. Landers therefore re-introduce the 'hit and miss' gamble effect. (They also don't seem to last as long as an orbiter, either).

What did Huygens achieve? Pity it didn't last longer .. that may have been the only chance of putting a lander on Titan for long, long time. Was it a gamble too (that didn't really pay off so well?)

Colin Robinson
2013-Jun-11, 06:09 AM
The search for life in the universe, is secondary to the fundamental drive to gain scientific knowledge. Without such a driver, the search for life elsewhere, would remain where it was in the dark ages.

IMO, the search for life is not necessary in a strategy for achieving the broader focused goal. In fact it undermines it .. because its motives are largely philosophical, and are thus a gamble.

I agree with you to some extent. Searching only for life when exploring the solar system would not be the wisest strategy. (It might be a bit like looking for needles in a haystack when you don't know anything about ordinary hay.) I see the search for answers/clues about the place of life in the universe (not only "elsewhere" but here in Earth too), as part of a more general search for answers about the cosmos we find ourselves in.

Nonetheless, finding out about the role of life in the universe is a topic of huge interest to lots of people, including both scientists and the general public. It is one of the motivating forces behind projects like Curiosity and Cassini. Neither Curiosity nor Cassini is looking for life directly, but both are contributing to research that is related to the life-in-space topic — e.g. because both missions are testing for organic compounds.


You assume a lander might be necessary for life detection and origin clues(?).. I notice one possible end to the Cassini mission, is for the spacecraft to aerobrake in Titan's atmosphere, and enter into long-term orbit around it. This would enable study of the atmospheric characteristics at lower altitudes. The study of PAHs might therefore be achievable without the need for a lander (as an eg). Landers also localise the searchable terrain, as opposed to enabling the global perspective achievable from orbit .. Landers therefore re-introduce the 'hit and miss' gamble effect. (They also don't seem to last as long as an orbiter, either).

It's true that orbiters can provide a lot of information about the big picture of another planet or moon. But if we want (for instance) to distinguish between microbiology and complex organic chemistry, I don't really see how you could do that from orbit.


What did Huygens achieve?

Huygens was the first of its kind — the first and so far only device that has landed somewhere in the outer solar system. Even if it did nothing except demonstrate the feasibility of landings, it would have been a great achievement. In fact it did a lot more than that.


Pity it didn't last longer .. that may have been the only chance of putting a lander on Titan for long, long time. Was it a gamble too (that didn't really pay off so well?)

It wasn't designed to last. It was designed mainly to sample the atmosphere and take photos as it descended, though it also had instruments to test the surface as it landed, and to keep taking photos for a short time after touch-down. All of which it did.

The thing is, very little was known about conditions on the surface of Titan before the Cassini-Huygens mission got there. A larger lander, designed for a longer active life, would have been much more of a gamble, because of the risks involved in landing on unknown and largely unpredictable terrain.

Paul Wally
2013-Jun-11, 11:12 AM
How important is Titan in the search for answers or clues about life in the universe?

I think Titan is very important, for the following two reasons:

1.Because it might have life: life that is chemically very different to life on Earth. This would mean a second abiogenesis, with huge implications for the prevalence of life in the universe.

2.Because it might not have life. In which case it will tell us something about how complex organic molecules behave and interact in a planet-sized environment without organisms. Again, the implications are huge.

G.Gaylord Simpson compared search for life beyond Earth to a gamble at long odds.

If Titan is seen only as a place to look for life, then yes, sending a lander there would be a gamble. However, if Titan is considered as a place to look for life and to look for clues about the origin of life, then it is not a gamble at all.

I agree, especially with your second point. Actually, any planetary environment with a highly complex chemistry is of relevance to understanding how life
could emerge. Because of the spatial and temporal scales involved, each planetary environment is a large scale chemical laboratory, something that we are unable to recreate on Earth. There is chemical evolution wherever there is matter, but in some locations complexity emerges and in others not, so the scientific problem is to understand how and why complexity emerges in some environments and not in others. The answers to these questions are in themselves relevant to understanding the emergence of life, which is really just a special case of complexity emergence.

Colin Robinson
2013-Jun-12, 12:59 AM
I agree, especially with your second point. Actually, any planetary environment with a highly complex chemistry is of relevance to understanding how life
could emerge. Because of the spatial and temporal scales involved, each planetary environment is a large scale chemical laboratory, something that we are unable to recreate on Earth. There is chemical evolution wherever there is matter, but in some locations complexity emerges and in others not, so the scientific problem is to understand how and why complexity emerges in some environments and not in others. The answers to these questions are in themselves relevant to understanding the emergence of life, which is really just a special case of complexity emergence.

If we think of life in that sort of way, as a special case of complexity, doesn't it also strengthen the case for my first point — that the global chemistry on Titan may have generated complex systems that grow and evolve — an exotic form of life?

Selfsim
2013-Jun-12, 02:05 AM
The problem here is that Colin's original two 'reasons' imply that a reality exists where either (for Titan):
i) there may be life (exotic) or;
ii) there may not be life.

We don't know that those are the only clear-cut possibilities, before sending a test probe there, nor do we know where to send it.

We only know of tests for carbon based life. We have no tests for other non-Earth sourced 'exotic life'. We have no idea of what 'exotic' forms of life actually might do (in order to test for those things). Therefore, the hypothesis about 'exotic life' is not testable unless it functions as terrestrial life does and we have no idea beforehand, if 'exotic' life on Titan does that, or 'sort of does that', or 'doesn't sort of do do that', etc.

Conceiving of exotic Titian life, does not get us anywhere as far as testing is concerned, until we know how to distinguish it from other chemistry going on there. If the purpose of sending a probe there is to test for 'exotic life', then its going to be going with an empty set of tests aboard(!?)

We're havin' enough troubles trying to decide whether or not Mars has/had carbon terrestrial based life .. or even organics! And Mars is well within a habitable zone. Titan is well outside of it .. so those conditions could just as well make all the difference. Testing in the lab at Titan temperatures, is also not straight-forward because of those cold temperatures.

Come to think of it, we still have a hard time trying to decide whether or not things like nanobes (nanons) etc are in fact life (or not). We had the same problem with the ALH84001 meteorite structures.

We really have no idea of what to look for/test on Titan .. except maybe a bunch of wild imaginings like McKay's. What effect do those have on 'the gamble'?

Using 'the hunt for life' as the basis for exploring Titan, is flawed and fatally so, I'm afraid.

Colin Robinson
2013-Jun-12, 03:18 AM
The problem here is that Colin's original two 'reasons' imply that a reality exists where either (for Titan):
i) there may be life (exotic) or;
ii) there may not be life.

We don't know that those are the only clear-cut possibilities,

OK. Another possibility is that there are dynamic systems which we'll find difficult to classify either as life or non-life.


before sending a test probe there, nor do we know where to send it.

We only know of tests for carbon based life. We have no tests for other non-Earth sourced 'exotic life'. We have no idea of what 'exotic' forms of life actually might do (in order to test for those things). Therefore, the hypothesis about 'exotic life' is not testable unless it functions as terrestrial life does … and we have no idea beforehand, if 'exotic' life on Titan does that, or 'sort of does that', or 'doesn't sort of do do that', etc.

Conceiving of exotic Titian life, does not get us anywhere as far as testing is concerned, until we know how to distinguish it from other chemistry going on there. If the purpose of sending a probe there is to test for 'exotic life', then its going to be going with an empty set of tests aboard(!?)

We're havin' enough troubles trying to decide whether or not Mars has/had carbon terrestrial based life .. or even organics!

That's one difference between Mars and Titan: it is established that Titan has plenty of organic compounds.

How do the organics behave and interact on Titan, what sort of systems, complex or simple, have emerged? These are questions that future missions to Titan can address.

If it turns out that there are comparatively complex systems of chemical reactions, systems which do things like grow and evolve, then the question will arise whether they should be classified as living things.


And Mars is well within a habitable zone. Titan is well outside of it .. so those conditions could just as well make all the difference. Testing in the lab at Titan temperatures, is also not straight-forward because of those cold temperatures.

Come to think of it, we still have a hard time trying to decide whether or not things like nanobes (nanons) etc are in fact life (or not). We had the same problem with the ALH84001 meteorite structures.

We really have no idea of what to look for/test on Titan .. except maybe a bunch of wild imaginings … like McKay's.

Chris McKay's argument may seem wild to you, Selfsim, but it is founded on well-known principles of thermodynamics and basic chemistry, and it meets the criterion of falsifiability.


Using 'the hunt for life' as the basis for exploring Titan, is flawed and fatally so, I'm afraid.

Not the "hunt for life", but the "search for answers/clues about life", is the stated topic of this thread.

Selfsim
2013-Jun-12, 07:38 AM
Not the "hunt for life", but the "search for answers/clues about life", is the stated topic of this thread.Well, that's the stated title of the thread, but the question of:


... How do the organics behave and interact on Titan, what sort of systems, complex or simple, have emerged? These are questions that future missions to Titan can address. ... would seem to be a much broader goal, which doesn't pre-empt any particular outcome(s) ...

One which I'd happily be onboard with!
It removes 'the gamble', assures returns for science, and is complelely independent of any speculative life hypotheses dreamed up for the case of Titan.

Designing instruments with that goal in mind, stands a reasonable chance of eliminating uncertainties .. as opposed to one which deliberately introduces them, no(?)

TooMany
2013-Jun-12, 04:45 PM
We're havin' enough troubles trying to decide whether or not Mars has/had carbon terrestrial based life .. or even organics! And Mars is well within a habitable zone. Titan is well outside of it .. so those conditions could just as well make all the difference. Testing in the lab at Titan temperatures, is also not straight-forward because of those cold temperatures.
...
We really have no idea of what to look for/test on Titan .. except maybe a bunch of wild imaginings like McKay's. What effect do those have on 'the gamble'?

Using 'the hunt for life' as the basis for exploring Titan, is flawed and fatally so, I'm afraid.

You seem to assert that we need to know precisely what to look for, but since we don't, no progress is possible. That simply isn't true. We don't know precisely what to expect if there is some form of life. We can obtain far more information on Titan's chemistry without knowing what is possible. Moreover, even if we do go there with some foolish, preconceived notion of what life to expect then we may or may not confirm or deny that hypothesis but there will still be plenty of data generated to give us a clue about what to look for next.

You statement, that a hunt for life is fatally flawed is incorrect. We cannot help but learn even if we don't send the best possible probe experiments and fail to conclusively confirm or deny life. I am not aware of any constraints that astrobiologist are imposing on a search for life on Titan. In fact I very much doubt that a Titan mission will have that as a goal, simply because we don't know what to look for. Instead, future missions we seek to better understanding of conditions, chemistry and geology. As we learn, we can decide what to do next.



Come to think of it, we still have a hard time trying to decide whether or not things like nanobes (nanons) etc are in fact life (or not). We had the same problem with the ALH84001 meteorite structures.

If we look at abiogenesis with some rigid definition of life then we will never make sense of it. There cannot be a sharp boundary between nonliving and living. Such a boundary would demand that extremely evolved systems that metabolize, use encoded instructions and make replicas of themselves simply popped into existence. There is likely a long path from non-life to life of that sort. The entities that exist along that path may show some aspects of what we consider life, but not others. Whether nanons are "life" is just not a sensible question to ask about them. They do not meet the complexity that we require in the definition of "life". The interesting question to ask is "are entities like nanons forms that lie on that path from non-life to life?"

Paul Wally
2013-Jun-12, 08:37 PM
If we think of life in that sort of way, as a special case of complexity, doesn't it also strengthen the case for my first point — that the global chemistry on Titan may have generated complex systems that grow and evolve — an exotic form of life?

Possibly. We do need some more hypotheses about life on Titan. Because the conditions on Titan are so different and because we know so little about the surface conditions, especially the exact composition of the lakes, I find it difficult to come up with possible life forms. I think where one could start is to look at the nature of organic and inorganic chemistry under Titan-like conditions. What are the reaction rates at those low temperatures? How does methane behave as a liquid etc. Once we have a set of ground rules, it should become much easier to speculate on possible life-forms.

Selfsim
2013-Jun-12, 09:32 PM
Its good to see we're all in agreement then.

So just restating Colin's OP words:

if Titan is considered as a place to look for life and to look for clues about the origin of life, then it is not a gamble at all.So what we've come up with is .. forget the life/nolife thinking .. its a gamble.
Go for an understanding of the chemistry.

Sounds good to me.

Actually, the case of Titan accentuates the dilemma we have when it comes to 'life as we know it' (LAWKI) detection missions. This dilemma is even more noticeable when it comes to 'life as we don't know it' (LAWDKI) - which is exactly what Titan means for 'The Quest' (life/nolife elsewhere).

The only LAWKI mission that's happened so far, was Viking. Now according to another CQ poster (and to Gil Levin), life was detected on Mars, and yet very few others seem to know about it. This would be the risk, or the gamble, that Colin's Gaylord Simpson quote must be referring to(??)

Amusingly, if we had some kind of LAWKI technology which was so small, as to be insignificant compared with the spacecraft which carries it, I think the whole matter might become a moot point, eh? .. That's provided it can return unambiguous results, that is which I think is the real issue dividing the 'life detection' mission camp from the 'forget life detection' mission camp(?)

The unambiguous detection of life elsewhere, would depend almost entirely on the nature of the specimen discovery itself, so in my opinion, at present, its unambiguous diagnosis would take multiple missions to retrieve all the necessary data to distinguish the specimen from the environment (again, basing this on what I think everyone here might be thinking about when they speak of say, Titan 'life' - ie: organic (methane based?) microbiological in size and characteristics(?) - then again, that assumption may be wrong, too). So if multiple missions are what is presently required for life detection on a 'local' world, then we have another distinguishing characteristic for what we mean when we say 'life detection' missions?

TooMany
2013-Jun-12, 11:30 PM
The possibility that life (on Mars) does exists but not on the surface and not uniformly argues against direct life-detection experiments at this time. Negative results of such experiments will be viewed by many as proof of nonexistence of life on Mars. This may limit funds for future missions. So rather than staying in that dilemma, NASA has made the right decision in not repeating a Viking-type experiment. There will always be arguments about whether remote results are unambiguous, but negative results could be damaging to the whole program.

In the case of Titan, at this point it would be positively silly to send a "life-detection" experiment since we don't even know whether life nor what sort of life could exist under those conditions.

Colin Robinson
2013-Jun-12, 11:45 PM
If we look at abiogenesis with some rigid definition of life then we will never make sense of it. There cannot be a sharp boundary between nonliving and living. Such a boundary would demand that extremely evolved systems that metabolize, use encoded instructions and make replicas of themselves simply popped into existence. There is likely a long path from non-life to life of that sort. The entities that exist along that path may show some aspects of what we consider life, but not others. Whether nanons are "life" is just not a sensible question to ask about them. They do not meet the complexity that we require in the definition of "life". The interesting question to ask is "are entities like nanons forms that lie on that path from non-life to life?"

Yes. And if Titan has forms of organic chemistry which are on that path from non-life to life, then studying those forms can be part of our path from not knowing to knowing about how life happens.

Colin Robinson
2013-Jun-13, 12:26 AM
Well, that's the stated title of the thread, but the question of:


How do the organics behave and interact on Titan, what sort of systems, complex or simple, have emerged? These are questions that future missions to Titan can address.

... would seem to be a much broader goal, which doesn't pre-empt any particular outcome(s) ...

One which I'd happily be onboard with!

That you and I agree on something, seems like a breakthrough in itself.

Titan, here we come!

Selfsim
2013-Jun-13, 12:49 AM
That you and I agree on something, seems like a breakthrough in itself. Oh you and I agree on heaps of things .. (Don't let others convince you otherwise, Colin. :) .. They are simply mistaken.)


Titan, here we come!Cassini is already there!

Colin Robinson
2013-Jun-13, 03:43 AM
The unambiguous detection of life elsewhere, would depend almost entirely on the nature of the specimen discovery itself, so in my opinion, at present, its unambiguous diagnosis would take multiple missions to retrieve all the necessary data to distinguish the specimen from the environment (again, basing this on what I think everyone here might be thinking about when they speak of say, Titan 'life' - ie: organic (methane based?) microbiological in size and characteristics(?) - then again, that assumption may be wrong, too).

I think micro life on Titan is generally considered more plausible than large multi-celled forms there. This is basically because microbes require less energy than the larger living things.

(Someone is probably thinking, aren't Titan's hydrocarbons an excellent energy source? The answer is that they would be, if there was free oxygen in the atmosphere. Unfortunately there is almost no oxygen. On the other hand, Titan's atmosphere does have hydrogen, which generates energy if you combine it with hydrocarbons other than methane. But the amount of free hydrogen on Titan does not provide the sort of abundant chemical energy available from the free oxygen here on Earth.)

The suggestion that life might be "methane-based" is because chemical reactions are facilitated by a liquid medium, and methane (as well as ethane) is a plentiful liquid on Titan's surface.

Paul Wally
2013-Jun-17, 09:13 PM
I think micro life on Titan is generally considered more plausible than large multi-celled forms there. This is basically because microbes require less energy than the larger living things.


How about large single-celled lifeforms? Why do single celled lifeforms have to be just as small everywhere as they are here on Earth?

TooMany
2013-Jun-17, 10:39 PM
How about large single-celled lifeforms? Why do single celled lifeforms have to be just as small everywhere as they are here on Earth?

Maybe they don't if based on some other chemistry. For earth life there are limits to cell size determine by the ability to transport molecules around within the cell and through cell membranes. To get larger creatures you need circulatory systems made up of many cells, I suppose.

Selfsim
2013-Jun-17, 11:22 PM
Maybe they don't if based on some other chemistry. For earth life there are limits to cell size determine by the ability to transport molecules around within the cell and through cell membranes. To get larger creatures you need circulatory systems made up of many cells, I suppose.'Valonia ventricosa' (https://en.wikipedia.org/wiki/Single-cell_organism) can reach a diameter of 1 to 4 cms and is one of the biggest known single-celled organisms … There are some big ones in the Challenger Deep (Marianas Trench), too.

Colin Robinson
2013-Jun-17, 11:25 PM
Maybe they don't if based on some other chemistry. For earth life there are limits to cell size determine by the ability to transport molecules around within the cell and through cell membranes.

Yes. It has been argued that in conditions where chemical changes occur more slowly, cells would not need to have as high a ratio of surface-area to volume as on Earth. A paper by Dirk Schulze-Makuch and David Grinspoon says

"In an extremely cold, hydrophobic (but liquid) environment, surface/volume ratio considerations may be less constraining than at higher temperatures in polar solvents. Thus, life on Titan could involve huge (by Earth standards) and very slowly metabolizing cells"

Biologically Enhanced Energy and Carbon Cycling on Titan? (http://cips.berkeley.edu/events/planets-life-seminar/schulze.pdf)

The point as I understand it is this:

Conditions with an overall slower rate of chemical change would make it difficult for organisms to metabolize as fast as happens on Earth; on the other hand, they wouldn't necessarily need to metabolize as fast, because slow chemistry would also mean their biomolecules would not tend to break down as fast as here, and so would not need to be rebuilt as often. Hence they may not need the same rate of chemical interaction with their surroundings, in terms of absorbing nutrients and expelling wastes thru the cell wall.

Colin Robinson
2013-Jun-17, 11:30 PM
'Valonia ventricosa' (https://en.wikipedia.org/wiki/Single-cell_organism) can reach a diameter of 1 to 4 cms and is one of the biggest known single-celled organisms … There are some big ones in the Challenger Deep (Marianas Trench), too.

So, even if Titan organisms are all single-celled, we might not need a microscope to photograph one...

Selfsim
2013-Jun-17, 11:59 PM
So, even if Titan organisms are all single-celled, we might not need a microscope to photograph one...Interesting .. the Grinspoon etal point is more about meagre energy levels, (comparatively with Earth), possibly resulting in smaller lifeforms .. but I would think the ratio of available energy (and what it takes to capture it): to the minimal amount required to sustain life in a given habitat, (whatever that might be), might be a more robust way to think about it(?)

I mean potentially, the ratio could just as easily be the same everywhere for a given defined habitat (sort of like a universal life constant)… which would imply lifeforms of the same size everywhere, for the same defined habitat, (or slight variations from it).

… If not, why not(?) .. after all, this is the same principle of habitability applied when looking for Earth-like planets isn't it?

TooMany
2013-Jun-18, 12:11 AM
'Valonia ventricosa' (https://en.wikipedia.org/wiki/Single-cell_organism) can reach a diameter of 1 to 4 cms and is one of the biggest known single-celled organisms There are some big ones in the Challenger Deep (Marianas Trench), too.

Truly bizarre. But this is very uncommon, although it isn't clear why, if this algae can do it. One of its plant advantages is the use of cellulose to construct its cell wall.

The more I learn about signal-celled animals the more amazed I am by their complexity. It's clear that these single-celled plants and animals are actually highly evolved life forms and nothing one could suggest as a very simple form of life.

Colin Robinson
2013-Jun-18, 03:26 AM
Interesting .. the Grinspoon etal point is more about meagre energy levels, (comparatively with Earth), possibly resulting in smaller lifeforms .. but I would think the ratio of available energy (and what it takes to capture it): to the minimal amount required to sustain life in a given habitat, (whatever that might be), might be a more robust way to think about it(?)

I mean potentially, the ratio could just as easily be the same everywhere for a given defined habitat (sort of like a universal life constant)… which would imply lifeforms of the same size everywhere, for the same defined habitat, (or slight variations from it).

… If not, why not(?) .. after all, this is the same principle of habitability applied when looking for Earth-like planets isn't it?

Aren't there several different issues here:

* Temperature levels.
* Level of available energy - energy that can sustain a dynamic system; which is not the same as temperature.
* General rate of chemical reactions at different temperatures and in different liquid mediums.
* What sort of metabolic rate is possible in particular conditions?
* What metabolic rate is needed in particular conditions to counteract damage from destructive chemical reactions?
* What follows, in terms of necessary ratio between cell-wall area and cell volume?
* How do the energy requirements of multi-celled life differ from those of single-celled?

I don't see how you would get a universal constant, with life-forms of the same size everywhere?

Colin Robinson
2014-Dec-07, 11:57 PM
I agree, especially with your second point. Actually, any planetary environment with a highly complex chemistry is of relevance to understanding how life
could emerge. Because of the spatial and temporal scales involved, each planetary environment is a large scale chemical laboratory, something that we are unable to recreate on Earth. There is chemical evolution wherever there is matter, but in some locations complexity emerges and in others not, so the scientific problem is to understand how and why complexity emerges in some environments and not in others. The answers to these questions are in themselves relevant to understanding the emergence of life, which is really just a special case of complexity emergence.

Can the astrobiological importance of Titan be summed up as follows?

"Life as we know it" is a form of self-organisation of matter made possible by a planetary environment conducive to chemical reactions. What else besides LAWKI can happen in a planetary environment conducive to chemical reactions?

Titan's atmosphere and surface, with its organic compounds, liquid lakes, and unearthly temperature, offers a specific partial answer to this "what else?" question. Its answer may be a particular class of "life as we don't know it", or it may be a class of complex chemistry as we don't know it.

Paul Wally
2014-Dec-27, 09:47 PM
Can the astrobiological importance of Titan be summed up as follows?

"Life as we know it" is a form of self-organisation of matter made possible by a planetary environment conducive to chemical reactions. What else besides LAWKI can happen in a planetary environment conducive to chemical reactions?

It depends on what we mean by LAWKI ... I suppose. We may find something that's life-like, in that it might have certain properties
in common with LAWKI while having certain other novel properties. I'm not too fond of the distinction LAWKI/LAWDKI though. Life is whatever we define it to be, just like "planet". Pluto is no longer called a planet, but that is not because Pluto has changed in any way.



Titan's atmosphere and surface, with its organic compounds, liquid lakes, and unearthly temperature, offers a specific partial answer to this "what else?" question. Its answer may be a particular class of "life as we don't know it", or it may be a class of complex chemistry as we don't know it.

For me it's not clear what would count as "life as we don't know it". Suppose that on Titan there is a class of complex chemistry that we don't know, but it still has general features like reproduction, and metabolism, growth, evolution etc. In a more general sense it would be life as we know it, but when it comes to the details then it's life as we don't know it.

Colin Robinson
2014-Dec-27, 11:21 PM
It depends on what we mean by LAWKI ... I suppose. We may find something that's life-like, in that it might have certain properties
in common with LAWKI while having certain other novel properties. I'm not too fond of the distinction LAWKI/LAWDKI though. Life is whatever we define it to be, just like "planet". Pluto is no longer called a planet, but that is not because Pluto has changed in any way.

True. It may turn out that the answer to the question "is there life on Titan" will depend not on what we find there, but on an institutional decision about what counts as "life" and what doesn't. But whichever way the decision went, it would not lessen the scientific importance of finding something beyond Earth which was, as you put it, "life-like".


For me it's not clear what would count as "life as we don't know it". Suppose that on Titan there is a class of complex chemistry that we don't know, but it still has general features like reproduction, and metabolism, growth, evolution etc. In a more general sense it would be life as we know it, but when it comes to the details then it's life as we don't know it.

Yes. It would be "as we know it" in terms of what it does, but not in terms of what it is made of.