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Colin Robinson
2012-Oct-27, 06:44 AM
From the thread "Contact: What happens if a Signal is found?"


There's way more to it than the base chemistry (and I think you know it).

So can you elaborate and go into some specifics for us? Could you also please outline why a hypothesised Titan dwelling methanogen, might present us with Earth-like life signs, in the first place? (Ie: Why?)

I think this topic deserves a thread of its own.

The term "Earth-like" in the title of this thread is based on the wording of Selfsim's question. However, I am not very comfortable with the term "Earth-like"...

Given that Earth and Venus both have lightning, does that mean that the lightning on Venus is "Earth-like"? Or perhaps we should call lightning on Earth "Venus-like"? The real question (as I see it) is whether Earth life has aspects that are universal, as well as aspects that result from local conditions and/or contingent events?

Life is a complex dynamic system, and complex dynamic systems can behave in similar ways even when they are composed of different stuff. For instance, the clouds of Earth are made of water, whereas the clouds of Venus are made of sulfuric acid, yet both sorts of clouds produce thunder and lightning.

Life on the surface of Titan would need to be made of different stuff than life on the surface of Earth. In which case, can it be expected to behave in similar ways to Earth, for example, by combining hydrogen with a carbon compound to produce methane? As argued by Ousama Abbas, Dirk Schulze-Makuch, David Grinspoon, Chris McKay and Heather Smith.

I think yes, their argument is a reasonable one. Why? Because it's based on the principles of thermodynamics, and these principles apply just as much to a living cell as to a machine... The same thermodynamic principles apply whether a machine is made out of wood or metal or plastic... And they would apply just as much to a organism whose internal solvent was methane or ethane or ammonia, as to a cell whose solvent was water...

Paul Wally
2012-Oct-27, 11:54 AM
Earth-like life would have a set of features characteristic of Earth-like life. For example the particular biochemistry i.e. particular nucleic acids, amino-acids, particular chemical processes. But things like reproduction, metabolism, evolution, homeostasis are features of life in general. If life on Titan reproduces, metabolizes, evolves, and maintains an internal equilibrium, we wouldn't call it Earth-like for those reasons. We would just call it life, because those are characteristics of life-like phenomena. If we find, in addition to those general features, that life on Titan also has DNA, and has the same biochemistry as Earth-life then we would be more justified in calling such life Earth-like.

We don't say that a mouse is cat-like. Mice and cats are mammals and they share mammalian features, just like all life shares life-like features. Therefore when we look for life on Mars or Titan we look for life-like features not Earth-like features.

Colin Robinson
2012-Oct-28, 04:48 AM
Earth-like life would have a set of features characteristic of Earth-like life. For example the particular biochemistry i.e. particular nucleic acids, amino-acids, particular chemical processes. But things like reproduction, metabolism, evolution, homeostasis are features of life in general. If life on Titan reproduces, metabolizes, evolves, and maintains an internal equilibrium, we wouldn't call it Earth-like for those reasons. We would just call it life, because those are characteristics of life-like phenomena.

How feasible or not do you think it is to look for something on Titan that reproduces, metabolizes, evolves, and maintains an internal equilibrium?

Consider this recent statement (a reply to a question) by NASA Astrobiology Senior Scientist David Morrison (https://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=20539)


we have pursued a “follow the water” path in most recent discussions of searching for life. There are two very good reasons. The first is that we think we know how to recognize water-based life, while no one knows what might be expected with other solvents. We do not know what chemical tests we could apply to identify such life “as we don’t know it”. The second reason is that the water-carbon combination permits much larger and more complex organic molecules than any other materials. Thus we think that a water and carbon based life is objectively the most probable. The risk, of course, is that we might rationalize our belief that carbon life is most likely (because it is easiest to identify) and therefore will not do sufficient research on other possible life forms.

Applying a "follow-the-water" strategy strictly would mean not looking for life in Titan's surface lakes of methane/ethane... Would life with another solvent really be too difficult to identify? Is it time for a more inclusive strategy than "follow the water"?

Selfsim
2012-Oct-28, 10:25 AM
while no one knows what might be expected with other solvents. We do not know what chemical tests we could apply to identify such life “as we don’t know it”. The second reason is that the water-carbon combination permits much larger and more complex organic molecules than any other materials.You both missed the point ...
Titan has no liquid surface water. Its surface liquid is primarily methane .. methane lacks the polarity of water, and thus would not be a good transporter of polar molecules within a 'cell' (or its equivalent). 'Life' is critically dependent on transport of polar molecules within cells. 'Life' processes cannot function without this physical intra-cell transport mechanism.
All of the following functions:
... reproduces, metabolizes, evolves, and maintains an internal equilibriumare the resultants of the fundamental solute/solvent characteristic of liquid water. Thus, your definition of generalised 'life', is specific to 'Earth-like' environments which possess liquid water.

Thus far, water (probably liquid) is quite widespread throughout our Solar System and yet, we have no obvious 'generalised' signs of life within it. Liquid water may not necessarily result in life, and 'generalised' life functions can't do without it!

The fact is that we simply do not know anything about life outside of the Earth. Our best 'generalisations' are guesses, at best. Drawing inference from a guess, results in more guesswork ....

Van Rijn
2012-Oct-28, 10:44 AM
You both missed the point ...
Titan has no liquid surface water. Its surface liquid is primarily methane .. methane lacks the polarity of water, and thus would not be a good transporter of polar molecules within a 'cell' (or its equivalent). 'Life' is critically dependent on transport of polar molecules within cells.


You should have "Earth" or "known" before "'Life' is critically dependent on . . ." We do not know that all life must require this.



Liquid water may not necessarily result in life, and 'generalised' life functions can't do without it!


You're assuming too much. We don't know that "generalized" life functions require water.



The fact is that we simply do not know anything about life outside of the Earth. Our best 'generalisations' are guesses, at best. Drawing inference from a guess, results in more guesswork ....

Yet you're making claims about critical dependencies and requirements.

Paul Wally
2012-Oct-28, 11:01 AM
How feasible or not do you think it is to look for something on Titan that reproduces, metabolizes, evolves, and maintains an internal equilibrium?

This is a very interesting question; how we would design experiments capable of distinguishing between biological and non-biological chemical processes.
Perhaps the first thing to test is whether there is an active chemistry going on. For instance what would happen if we took a sample and chemically isolate it from the environment keeping everything else unchanged? There should be a change in the ratios between the various substances as a function of time, just like when we put a plant in a sealed container the CO2 level drops while the O2 level rises.

So, we get a system with inputs and outputs and the problem is just to find out whether the transfer function is characteristic of biological systems. Biological systems being fundamentally cybernetic, it shouldn't be too difficult to test for things like chemotaxis for example. Actually, I think the biggest feasibility issue is with getting the instruments to work in the cryogenic environment, rather than the problem of life-detection.



Applying a "follow-the-water" strategy strictly would mean not looking for life in Titan's surface lakes of methane/ethane... Would life with another solvent really be too difficult to identify? Is it time for a more inclusive strategy than "follow the water"?

While I don't think the "follow the water" is a bad strategy (water being made of the most abundant element and third most abundant element and also because we know so much about water-based biology), my view is that we should also follow complexity. That means that any conditions where complex physical and/or chemical processes can occur shouldn't be ruled out.

Selfsim
2012-Oct-28, 09:05 PM
You should have "Earth" or "known" before "'Life' is critically dependent on . . ." We do not know that all life must require this.Well then how do we know that ...
… things like reproduction, metabolism, evolution, homeostasis are features of life in general.???

The phrase 'in general', was intended as a basis for extrapolating life's 'features' to beyond Earth's environs .. so, I'll ask you … how do we know this??

What is to say that these functions might well represent some particular niche of some bigger process which may be way broader in definitional terms than this? (Or maybe, just the opposite … ie: that it might be caused by some property unique to just water)? The only thing which appears to constrain this claim, (so far implied in this conversation), is: "because that's what life does on Earth".


You're assuming too much. We don't know that "generalized" life functions require water.We do know that reproduction, metabolism, evolution, homeostasis require particular physical properties of the water molecule, which also happens to separate water apart from other substances, and which also makes it vital to sustaining extant life.


Yet you're making claims about critical dependencies and requirements.I didn't make the claim that ….

… things like reproduction, metabolism, evolution, homeostasis are features of life in general.

Colin Robinson
2012-Oct-28, 09:19 PM
You both missed the point ...
Titan has no liquid surface water. Its surface liquid is primarily methane .. methane lacks the polarity of water, and thus would not be a good transporter of polar molecules within a 'cell' (or its equivalent). 'Life' is critically dependent on transport of polar molecules within cells. 'Life' processes cannot function without this physical intra-cell transport mechanism.
All of the following functions:are the resultants of the fundamental solute/solvent characteristic of liquid water. Thus, your definition of generalised 'life', is specific to 'Earth-like' environments which possess liquid water.

Yes, it's true that all life on Earth contains liquid water, which functions as a solvent.

The question is whether this is because water is the only possible solvent of something that grows and metabolizes and maintains an internal equilibrium? Or is it rather because liquid water is abundant on Earth?

There are at least two environments in the Solar System where a liquid solvent other than water is present in abundance. By a solvent, I mean a liquid that can dissolve a wide range of stuff. One such environment is the surface of Titan, where there are methane/ethane lakes. The other environment is the clouds of Venus, where there is abundant sulfuric acid, in the form of aerosol droplets.

Methane lacks polarity, you say? Sulfuric acid, on the other hand, has more polarity than water... Perhaps that makes sulfuric acid a better solvent than water for a living, growing, metabolising system?


The fact is that we simply do not know anything about life outside of the Earth. Our best 'generalisations' are guesses, at best. Drawing inference from a guess, results in more guesswork ....

Drawing inferences from an educated guess at best results in propositions which can be falsified or verified by observations, e.g. via robot missions to the lakes of Titan or, for that matter, to the clouds of Venus...

Van Rijn
2012-Oct-28, 11:02 PM
Well then how do we know that ...???

The phrase 'in general', was intended as a basis for extrapolating life's 'features' to beyond Earth's environs .. so, I'll ask you … how do we know this??

What is to say that these functions might well represent some particular niche of some bigger process which may be way broader in definitional terms than this?


Then define your terms. What is your definition of "life"?



We do know that reproduction, metabolism, evolution, homeostasis require particular physical properties of the water molecule


We know reproduction, metabolism, evolution, and homeostasis requires the water molecule? Really? How are you defining these terms? Because I would say we know they don't require it.

Selfsim
2012-Oct-28, 11:22 PM
Yes, it's true that all life on Earth contains liquid water, which functions as a solvent.

The question is whether this is because water is the only possible solvent of something that grows and metabolizes and maintains an internal equilibrium? Or is it rather because liquid water is abundant on Earth?I agree. Until: (i) someone develops a reproducing, metabolising and homeostatic 'thing' in the lab or; (ii) a 'thing' is discovered somewhere which is absent of water and clearly not dependent on water's 'characteristic features', we will not be able to resolve such questions. (Yes .. your continuing enquiry will legitimately persist until this happens …)


There are at least two environments in the Solar System where a liquid solvent other than water is present in abundance. By a solvent, I mean a liquid that can dissolve a wide range of stuff. One such environment is the surface of Titan, where there are methane/ethane lakes. The other environment is the clouds of Venus, where there is abundant sulfuric acid, in the form of aerosol droplets.

Methane lacks polarity, you say? Sulfuric acid, on the other hand, has more polarity than water... Perhaps that makes sulfuric acid a better solvent than water for a living, growing, metabolising system?Sulfuric Acid is a strong polar mineral acid, (forms H+ ions (and its conjugates), when dissolved in water). It shows different properties depending on concentration. If concentrated, it shows strong dehydrating and oxidative properties.
The element Sulfur is present in Cysteine*, as a semi-essential amino acid, (ie: it can be biosynthesised in say, humans). In this process in for eg: humans however, it is derived from Methionine (which is an essential, non-polar amino acid), but in plants and bacteria, it starts from Serine (a polar precursor to proteins produced by the genetic code). Serine is important in metabolism and is the precursor to several other amino acids may include Glycine and others.
So, the Sulfuric Acid present in Venus' atmosphere is present due to the presence of trace water vapour. The reaction producing it, is by photodissociation of Carbon Dioxide, Sulfur Dioxide and Water vapour.

Once again, the significance of its polarity derived actions, (in terms of 'generalised life functions'), is dependent on the presence of water.

So, does it just happen that the Venus scenario serendipitously fits nicely into the so-called 'generalised' functions of life model .. because of the presence of trace amounts of liquid water, (yet again), which gives it is polar solvent properties, or are you saying that the properties of undissolved Sulfur Dioxide, (from which it originates), is a necessary precursor to 'life' (for the purposes of arguing the speculated 'generalised life functions')?


Drawing inferences from an educated guess at best results in propositions which can be falsified or verified by observations, e.g. via robot missions to the lakes of Titan or, for that matter, to the clouds of Venus...A robot mission to Titan or the clouds of Venus, would be a political decision based on popularity of an idea and its impact on resource prioritisation. In the light of an 'unknown' status of the physical reality of a phenomenon, such arguments may result in a decision, but this doesn't alter an unknown physical reality. An unbiased test from a balanced hypothesis and an element of pure luck, might however.

Paul Wally
2012-Oct-29, 12:35 AM
You both missed the point ...
Titan has no liquid surface water. Its surface liquid is primarily methane .. methane lacks the polarity of water, and thus would not be a good transporter of polar molecules within a 'cell' (or its equivalent). 'Life' is critically dependent on transport of polar molecules within cells. 'Life' processes cannot function without this physical intra-cell transport mechanism.

I think you're confusing necessity and sufficiency. We know that water in combination with other factors is sufficient for biological processes, but we don't know whether it is necessary. Maybe it is necessary, but we don't know that yet.


All of the following functions:are the resultants of the fundamental solute/solvent characteristic of liquid water. Thus, your definition of generalised 'life', is specific to 'Earth-like' environments which possess liquid water.

My definition of life is just that, a definition, and not an empirical statement about what exists. We can't make our definition of life too specific such as to exclude the possibility of non-Earth life from that definition, but neither can we make our definition too general that it includes things that we obviously do not consider to be life. The definition only says what general kinds of processes we should observe if it is to be called "life", and it says nothing about any specific chemistries capable of realizing those general kinds of processes.




What is to say that these functions might well represent some particular niche of some bigger process which may be way broader in definitional terms than this?

I would welcome such a broader definition, if it should be forthcoming. Bare in mind though that such a definition cannot include things that we definitely consider non-living on Earth otherwise the term "life" loses all meaning.


(Or maybe, just the opposite … ie: that it might be caused by some property unique to just water)

Whether or not that is the case is irrelevant. If we include in the definition of life that it must be water-based and we discover processes having all the generalised features except it isn't water based, then what shall we call it then?


The only thing which appears to constrain this claim, (so far implied in this conversation), is: "because that's what life does on Earth".

I would rather say: "... that's what the word "life" means on Earth." If that is what life does on Earth, then what would it mean for life to do something other than what it does on Earth? On what basis would we call it "life" if it has no general characteristics in common with Earth-life?

As an analogy, we have different kinds of mountains on Earth and from this we understand the meaning of the word "mountain". We can then look at Olympus Mons and immediately recognize it as a volcanic mountain, but we wouldn't call it an Earth-like mountain. The same with sulfuric acid clouds on Venus. We know that they are clouds because they have general cloud-like features, but they are definitely not Earth-like clouds.

Selfsim
2012-Oct-29, 12:49 AM
Then define your terms. What is your definition of "life"?I have no problems using the cited definitions for describing Earth-life .. I mean, after all, that's the biochemical basis from which where these terms came from, isn't it?


We know reproduction, metabolism, evolution, and homeostasis requires the water molecule? Really? How are you defining these terms? Because I would say we know they don't require it.So you know of some form of life which requires no water? Do tell … I'm eager to learn about it … what is it, where does it live and how does it metabolise, reproduce and control internal temperatures without using water's properties?

Selfsim
2012-Oct-29, 01:20 AM
I think you're confusing necessity and sufficiency. We know that water in combination with other factors is sufficient for biological processes, but we don't know whether it is necessary. Maybe it is necessary, but we don't know that yet.Try surviving without it … or better still, try asking for a glass of liquid methanol, or sulfuric acid next time you're at the pub … and see what happens to you own 'generalised life functions' after consuming it! :)


My definition of life is just that, a definition, and not an empirical statement about what exists. We can't make our definition of life too specific such as to exclude the possibility of non-Earth life from that definition, but neither can we make our definition too general that it includes things that we obviously do not consider to be life. The definition only says what general kinds of processes we should observe if it is to be called "life", and it says nothing about any specific chemistries capable of realizing those general kinds of processes. Perhaps you could try looking into your motivations for dwelling so much on a definition for life outside of Earth at all. Such a definition would only have meaning when such a thing as 'non-Earth-life' is actually discovered … For the 'life' of me <pun>, I cannot see any value coming from such 'musings' (apart from entertainment/sci-fi/political value, I suppose .)


I would welcome such a broader definition, if it should be forthcoming. Bare in mind though that such a definition cannot include things that we definitely consider non-living on Earth otherwise the term "life" loses all meaning.Perhaps the term 'life' has no meaning outside of Earth ..(??)...


Whether or not that is the case is irrelevant. If we include in the definition of life that it must be water-based and we discover processes having all the generalised features except it isn't water based, then what shall we call it then?

I would rather say: "... that's what the word "life" means on Earth." If that is what life does on Earth, then what would it mean for life to do something other than what it does on Earth? On what basis would we call it "life" if it has no general characteristics in common with Earth-life?Don't worry 'bout it .. until you find it .. sort it out, then.

(Ie: go where the data leads).


As an analogy, we have different kinds of mountains on Earth and from this we understand the meaning of the word "mountain". We can then look at Olympus Mons and immediately recognize it as a volcanic mountain, but we wouldn't call it an Earth-like mountain. The same with sulfuric acid clouds on Venus. We know that they are clouds because they have general cloud-like features, but they are definitely not Earth-like clouds.Does a cloud on Venus reproduce, metabolise and control its internal temperature?
I'd agree that clouds on Venus would have to be excluded from the definition of 'life' .. (otherwise, it loses its meaning).

eburacum45
2012-Oct-29, 06:23 AM
Perhaps you could try looking into your motivations for dwelling so much on a definition for life outside of Earth at all. Such a definition would only have meaning when such a thing as 'non-Earth-life' is actually discovered … For the 'life' of me <pun>, I cannot see any value coming from such 'musings' (apart from entertainment/sci-fi/political value, I suppose .)


This sort of speculation could allow astrobiologists to attempt to interpret data coming from planetary probes and exoplanetary observations. So far we haven't got any data that needs such interpretation, but at some point in the future it may come available to us. The search for 'non-Earth-life' is a bit like the search for gravity waves - we haven't seen any yet, but that shouldn't stop speculation about what their characteristics might be.

Even if 'non-Earth-life' is never discovered, this sort of speculation might have real benefits; if an alternative form of biochemistry can be synthesised, it might have great commercial value. Self-replicating organic systems that have different chemical characteristics to ordinary life could be very a very valuable commodity indeed.

Bobunf
2012-Oct-29, 06:55 AM
It seems to me that showing some thing on another celestial body engages in "reproduction, metabolism, evolution, homeostasis," etc. is likely to be staggeringly difficult. It will be necessary to:

> capture this thing in a way that does not disrupt it - made tougher because we don't how it works and thus don't know what might harm it;
> observe it reproduce - what if it takes centuries to reproduce?
> measure metabolic activity, made harder because we don't know what kind of metabolism, and thus don't know what to look for
> and how are you going to observe evolution?

On the other hand, for almost four billion years life on Earth has been changing its environment and very obviously affecting the Earth's atmosphere: methane, oxygen, ozone, freon, etc. The Earth's atmosphere has been out of thermal equilibrium for almost four billion years.

It's easy to construct an argument that modifications of the environment are a likely characteristic of life, and that such modifications likely would impact atmospheres. This, to me, is a much more feasible way to detect life, and not just life that uses the basics of Earth chemistry.

Selfsim
2012-Oct-29, 07:55 AM
This sort of speculation could allow astrobiologists to attempt to interpret data coming from planetary probes and exoplanetary observations. So far we haven't got any data that needs such interpretation, but at some point in the future it may come available to us. Are you serious?
Interpret probe data by running it through a completely speculative synthetic model, made up from some sketchy ideas, loosely based on grossly over-simplified structural analogies with Carbon/Water based life?
I can draw a picture of an alien in crayon ... would that suffice as an interpretive model?


Does this mean that The search for 'non-Earth-life' is a bit like the search for gravity waves - we haven't seen any yet, but that shouldn't stop speculation about what their characteristics might be.Gravity waves are well constrained in physical theory. Biology variants can only be constrained by empirical evidence of non-Earth based life, sythesised alternate biochemistries having measurable outcomes, or some other local discovery ... and there is none of any of 'em..


Even if 'non-Earth-life' is never discovered, this sort of speculation might have real benefits; if an alternative form of biochemistry can be synthesised, it might have great commercial value. Self-replicating organic systems that have different chemical characteristics to ordinary life could be very a very valuable commodity indeed.I'd agree that bio-engineering could produce some interesting results along the lines you're indicating. But bioengineering testing has controls and strong prior experimental justification. Its results should be able to be independently verifiable. There are many other real drivers behind such research .. none of which is associated in any way with a bunch of speculative dreams.

Selfsim
2012-Oct-29, 08:27 AM
It's easy to construct an argument that modifications of the environment are a likely characteristic of life, and that such modifications likely would impact atmospheres. This, to me, is a much more feasible way to detect life, and not just life that uses the basics of Earth chemistry.I'd agree that such an argument would have way more supporting evidence but yet again, derived Earth's particular situation. How the Earth-life by-product analogy translates for another planet/moon (etc) is not straightforward. The elimination of remotely sourced, non-biologically originated, false positive 'bio-sign' measurements, then becomes an issue. How does one eliminate an as yet undiscovered, natural, complex process, which might only occur in a specific environment that happens to differ from Earth's? (Ie: we already know these other natural, complex processes exist, from measurements/data taken from other planets/moons in our own Solar System).

MarianoRF
2012-Oct-29, 12:23 PM
Titan has no liquid surface water. Its surface liquid is primarily methane .. methane lacks the polarity of water, and thus would not be a good transporter of polar molecules within a 'cell' (or its equivalent). 'Life' is critically dependent on transport of polar molecules within cells. 'Life' processes cannot function without this physical intra-cell transport mechanism.
All of the following functions:are the resultants of the fundamental solute/solvent characteristic of liquid water. Thus, your definition of generalised 'life', is specific to 'Earth-like' environments which possess liquid water.

Thus far, water (probably liquid) is quite widespread throughout our Solar System and yet, we have no obvious 'generalised' signs of life within it. Liquid water may not necessarily result in life, and 'generalised' life functions can't do without it!

The fact is that we simply do not know anything about life outside of the Earth. Our best 'generalisations' are guesses, at best. Drawing inference from a guess, results in more guesswork ....

I totally agree with you. We are assuming that life out there is based on water... it could be... but we simply don't know. Could be based on another chemical compound, completely different to all that we know. And due to the fact that in Titan there's no water but methane and acetylene, if there's something alive there, it's using those chemical compounds to sustain its life.


You should have "Earth" or "known" before "'Life' is critically dependent on . . ." We do not know that all life must require this.

You're assuming too much. We don't know that "generalized" life functions require water

Correct. It's just what I said in another topic: maybe our mistake in the search of ET life, is that we are searching it with "human" eyes, and we are looking for something similar or equal (aka, water based). This of course, could be true, but we have to take into account other possibilities. And in the case that life out there is NOT water-based... how must we look for it? what kind of "life-detector" experiment should be make?


This is a very interesting question; how we would design experiments capable of distinguishing between biological and non-biological chemical processes.
Perhaps the first thing to test is whether there is an active chemistry going on. For instance what would happen if we took a sample and chemically isolate it from the environment keeping everything else unchanged? There should be a change in the ratios between the various substances as a function of time, just like when we put a plant in a sealed container the CO2 level drops while the O2 level rises.

So, we get a system with inputs and outputs and the problem is just to find out whether the transfer function is characteristic of biological systems. Biological systems being fundamentally cybernetic, it shouldn't be too difficult to test for things like chemotaxis for example. Actually, I think the biggest feasibility issue is with getting the instruments to work in the cryogenic environment, rather than the problem of life-detection.

While I don't think the "follow the water" is a bad strategy (water being made of the most abundant element and third most abundant element and also because we know so much about water-based biology), my view is that we should also follow complexity. That means that any conditions where complex physical and/or chemical processes can occur shouldn't be ruled out.

Totally agree! and very accurate. But taking a sample and isolating it, would require a machine capable of doing that, for example a rover or a fixed-station that can dig in the surface. We should definitely send more missions to Titan.

We shouldn't also forget Enceladus, where liquid water is present below the ice that covers the planet.

Paul Wally
2012-Oct-29, 04:11 PM
Try surviving without it … or better still, try asking for a glass of liquid methanol, or sulfuric acid next time you're at the pub … and see what happens to you own 'generalised life functions' after consuming it! :)

Toxicity is relative. We're breathing a once toxic gas called oxygen. And who is to say that water won't be toxic or even corrosive to organisms based on different biochemistries?


Such a definition would only have meaning when such a thing as 'non-Earth-life' is actually discovered …
Nope, that's not how it works. A definition gives criteria for identifying a discovery. In the case of a life-discovery those criteria would be a definition of life.


Perhaps the term 'life' has no meaning outside of Earth ..(??)...

That would be ruling out the possibility of life beyond Earth based on an a priori prejudice. You say that evidence is required but at the same time you say that the evidence is impossible. So you're blatantly contradicting yourself.


Don't worry 'bout it .. until you find it .. sort it out, then.

(Ie: go where the data leads).

You think that providing a definition requires some kind of prior empirical confirmation? A definition only provides testable criteria, it's not an empirical statement, i.e. a definition is neither true nor false.


Does a cloud on Venus reproduce, metabolise and control its internal temperature?
I'd agree that clouds on Venus would have to be excluded from the definition of 'life' .. (otherwise, it loses its meaning).

I see. So either you didn't understand the analogy or you are pretending not to understand it.


It seems to me that showing some thing on another celestial body engages in "reproduction, metabolism, evolution, homeostasis," etc. is likely to be staggeringly difficult.

It might be difficult, but I don't think it's impossible. It might even be easier than we thought, who knows.


capture this thing in a way that does not disrupt it - made tougher because we don't how it works and thus don't know what might harm it;

That would be one reason to first attempt to observe some kind of active chemistry, with minimal intervention. In my opinion the Viking experiments were too disruptive. If there are living organisms in the Martian soil then they are adapted to those conditions, and there would then be no need for us to provide them with anything.

If we only observe the open system on site, we might not observe any detectable changes in the relative concentrations of chemicals. In this case we might mistakenly see a dynamic equilibrium as a static situation. Especially in fluid environments, consumed products could be replenished while waste products rapidly diffuse to undetectable levels or are kept stable due to consumption by different organisms, but if we create a closed micro-environment then we might observe an increase in waste products and a decrease in consumables.



observe it reproduce - what if it takes centuries to reproduce?

What if it takes milliseconds to reproduce?

The logistics function could be an important indicator of reproductive growth it's also an indication of autocatalytic reactions (http://en.wikipedia.org/wiki/Autocatalysis).



measure metabolic activity, made harder because we don't know what kind of metabolism, and thus don't know what to look for

I'd say, once we distinguished the candidate organism from it's environment, we then have a black box model with inputs and outputs. Metabolism is whatever is happening inside the black box to produce the particular input-output responses. Through systematic study I see no reason why we wouldn't be able to figure out what's happening inside the black box. I would agree that remotely it is going to be somewhat difficult to study the more detailed biochemistry, but by that time we would already be pretty certain that it is a living organism.


and how are you going to observe evolution?

We can actually observe evolution in micro-organisms and small insects, due to their rapid reproduction and large populations. Drug resistant bacteria is an example. We could perform such experiments on alien microbes by changing the environmental conditions to see if they would adapt.

Selfsim
2012-Oct-29, 08:25 PM
... And who is to say that water won't be toxic or even corrosive to organisms based on different biochemistries?
I'm surprised that no-one has picked up on what I said before (see the underlined bit below):
Until: (i) someone develops a reproducing, metabolising and homeostatic 'thing' in the lab or; (ii) a 'thing' is discovered somewhere which is absent of water and clearly not dependent on water's 'characteristic features', we will not be able to resolve such questions. (Yes .. your continuing enquiry will legitimately persist until this happens …)There is a reasonable argument that water's quantum characteristics shape its behaviours in a way which directly promote Earth-life's 'generalised' life functions. (There is no evidence that 'generalised' life functions would be applicable for a planet devoid of liquid water).
The findings of a study into water's quantum behaviours was published in Physicsworld in Feb 2011: Physicists discover new quantum state of water: (http://physicsworld.com/cws/article/news/2011/feb/04/physicists-discover-new-quantum-state-of-water)

Water has a host of properties that set it apart from other substances and which make it particularly suited to sustaining life. For example, the fact that it is less dense as a solid than as a liquid and that its maximum density occurs at 4 °C, means that lakes freeze from the top-down rather than the bottom-up – something that was vital to sustaining life during ice ages.
...
The team argues that this is evidence that the protons exist in a previously unobserved quantum state when water is confined to a very tiny volume – a state that is not described by the electrostatic model. They say that whereas at the 0.1 nm distances that typically separate molecules only the intermolecular potential well exerts a significant force, at the 0.01 nm scale typical of an individual proton's potential well quantum fluctuations in charge that take place along the hydrogen bonds become significant. In this way the hydrogen bonds form what is known as a "connected electronic network" and they speculate that it is the response of the network to confinement that causes the large changes in proton energy.
...
According to Reiter, the quantum ground state that they have identified could be important to life because the confinement length typical of their experiments – about 2 nm – is roughly equal to the distances between structures within biological cells. "I think that the quantum mechanics of protons in water has been playing a role in the development of cellular life all along but we never noticed before," he says.
When one considers the cellular sub-processes which ultimately lead to 'generalised' Earth-life functions like metabolism, reproduction and homeostasis, the above evidence-based argument cannot be dismissed easily, and it also serves to reinforce the inseparability of water and life (without data coming from an instance of non-water based life from elsewhere).

Also interesting, is the point that electrostatic models cannot effectively describe this particular state, (so there are other factors to consider beyond the solute/solvent issues raised previously in this thread, when it comes to abiogenesis and subsequent evolution).

If quantum behaviours and electrostatic behaviours influenced the evolution of a cell, or even DNA molecule assembly, (I doubt that anyone could argue that they didn't), then what implications would this have for speculated non-Earth like, and non-water based 'exo-life'?*

Would the 'exo-life' enthusiasts out there say this 'increases' or 'decreases' the 'likelihood' of life in non-water-based exo-environments? (I only ask out of curiosity and politeness :surprised: .. the answer won't effect reality anyway ..)



*(Chuckle, chuckle … a question from me which invites even more speculation?? Man, I must be losin' it! :surprised: :p :) )

Selfsim
2012-Oct-29, 09:07 PM
I totally agree with you. We are assuming that life out there is based on water... it could be... but we simply don't know. Could be based on another chemical compound, completely different to all that we know. And due to the fact that in Titan there's no water but methane and acetylene, if there's something alive there, it's using those chemical compounds to sustain its life. … or … exo-life is something we dreamed up in the first place, and we're looking for a 'Holy Grail'.

Incidentally, I think you'll find that acetylene is all but absent in Titan's atmosphere (http://cosmoquest.org/forum/showthread.php/136925-News-from-Titan?p=2051306#post2051306) … but that's another story … When last I looked, it is hypothesised that speculated 'methanogens' on Titan are supposedly, and mysteriously, able to combine H2 with compounds 'like' acetylene (C2H2), and ethane, (C2H6), even though Earth's real methanogens do: CO2 + 4 H2 → CH4 + 2 H2O. Note that Earth's methanogens also require liquid water to do this (and exist). Hypothesised methanogens are thus, a wildly imagined speculative thing … primarily dreamed up by the notorious, and often wrong, (according to his own self-assessment), NASA 'Astrobiologist' and front-man, Chris McKay.

headrush
2012-Oct-29, 09:32 PM
Such a definition would only have meaning when such a thing as 'non-Earth-life' is actually discovered …

Nope, that's not how it works. A definition gives criteria for identifying a discovery. In the case of a life-discovery those criteria would be a definition of life.


(my bold)
How do you identify a discovery before it's discovered ?
And the criteria are defined by who exactly ? I'm pretty sure they will be earthlings, so the criteria will be earth "like".
I prefer the term constraints to criteria. Criteria are judgement points that you tick off to confirm a previous assumption or desire.
Constraints are conditions which absolutely have to be present. Of which we only have one set to go on so far.

Speculation is fine, but we only know one type of life to look for (no matter the method, atmospheric composition, biological function, reproduction). And anything we suppose is possible can only be measured against our own experience.
We will be surprised, I have no doubt. But a surprise it will be, not a prediction.

IMHO of course.

Paul Wally
2012-Oct-29, 10:35 PM
How do you identify a discovery before it's discovered ?

You identify it when you discover it, not before. However you cannot identify something as a kind of something if you don't have a prior definition or concept of that kind of something. In this case the kind of thing is life, but we cannot identify other instances of life if we don't already have a definition or concept of what life is.

Colin Robinson
2012-Oct-29, 11:21 PM
Yes, it's true that all life on Earth contains liquid water, which functions as a solvent.

The question is whether this is because water is the only possible solvent of something that grows and metabolizes and maintains an internal equilibrium? Or is it rather because liquid water is abundant on Earth?

I agree. Until: (i) someone develops a reproducing, metabolising and homeostatic 'thing' in the lab or; (ii) a 'thing' is discovered somewhere which is absent of water and clearly not dependent on water's 'characteristic features', we will not be able to resolve such questions. (Yes .. your continuing enquiry will legitimately persist until this happens …)

I'm glad you agree that my enquiry is legitimate.

Developing a new life-form in a lab would require very intricate nano-technology. However, the way scientists discuss this question is already grounded in laboratory experiments with different solvents.

There is a chapter about solvents in the report by Baross and others on Limits of Organic Life in Planetary Systems. (http://www.nap.edu/openbook.php?record_id=11919&page=69) Both methane and sulfuric acid are among the solvents discussed. (I know I've mentioned this publication before in related threads.)


Sulfuric Acid is a strong polar mineral acid, (forms H+ ions (and its conjugates), when dissolved in water).

This statement is founded on the Arrhenius definition of acidity/basicity, where everything is related to water and its ions, and nothing is considered either an acid or a base until it is added to water...

The Arrhenius definition is convenient for many purposes, simply because water is so ubiquitous, but there are other definitions of acidity/basicity which are more relevant to solvents other than water. To make clear which definition is being used, people use terms like "Arrhenius acid", "Lewis acid" etc.

See the Wikipedia article on Acid/base reaction (http://en.wikipedia.org/wiki/Acid–base_reaction).


So, the Sulfuric Acid present in Venus' atmosphere is present due to the presence of trace water vapour. The reaction producing it, is by photodissociation of Carbon Dioxide, Sulfur Dioxide and Water vapour.
Once again, the significance of its polarity derived actions, (in terms of 'generalised life functions'), is dependent on the presence of water.

So, does it just happen that the Venus scenario serendipitously fits nicely into the so-called 'generalised' functions of life model .. because of the presence of trace amounts of liquid water, (yet again), which gives it is polar solvent properties, or are you saying that the properties of undissolved Sulfur Dioxide, (from which it originates), is a necessary precursor to 'life' (for the purposes of arguing the speculated 'generalised life functions')?

It is true that the water molecule can serve as a raw material in production of sulfuric acid, H2SO4, and this seems to have happened in the atmosphere of Venus. But sulfuric acid is not just an aqueous solution of something. H2SO4 is a distinct molecule whose structure and characteristics (such as polarity) have been well studied.

The properties of sulfuric acid don't have much to do with those of sulfur dioxide, which is two chemical steps away. To get from SO2 to H2SO4, you need to add not only H2O, but also an additional atom of oxygen. Sulfur trioxide (SO3) is more closely related to sulfuric acid than sulfur dioxide is.


A robot mission to Titan or the clouds of Venus, would be a political decision based on popularity of an idea and its impact on resource prioritisation. In the light of an 'unknown' status of the physical reality of a phenomenon, such arguments may result in a decision, but this doesn't alter an unknown physical reality. An unbiased test from a balanced hypothesis and an element of pure luck, might however.

What do you mean by a "balanced hypothesis"?

Selfsim
2012-Oct-29, 11:55 PM
Such a definition would only have meaning ….
How do you identify a discovery before it's discovered ?What I'm saying is that we should associate no particular meaning with a tentative outline, (or guess), that comes with a hypothesis. It seems that, frequently, hypotheses are given ontological meaning (ie: like theories are .. but theories have some empirical data, and solid theoretical bases behind them. This non-water based life thing is pure conjecture, and therefore has no more meaning, than my crayon dawing of an alien. (Ie: as far as existence in the physical universe goes).
I might concede that we need some posits in order to get the process going, but these should be under continuous scrutiny and checking throughout the entire process. This is how mathematical induction works .. the inference used here is attempting to gain leverage from formalised logic (the most rigorous of which comes from mathematical induction), but its initial speculative posit, (ie: that exo-life exists), seems to be immune from ongoing scrutiny. Things like this are frequently (and conveniently) overlooked/forgotten ...


Speculation is fine, but we only know one type of life to look for (no matter the method, atmospheric composition, biological function, reproduction). And anything we suppose is possible can only be measured against our own experience.
We will be surprised, I have no doubt. But a surprise it will be, not a prediction.
Speculation is fine (in small quantities, and at the end of some informed, intensive study).

When speculation is over-emphasised ad nauseum, and becomes so familiar, it somehow turns into something more than just a whimsical idea .. the real science becomes distorted, as does the scientific perspective. Sci-fi emerges as the predominant paradigm … (and it usually goes largely unchecked).

In this case, our Earth-centric view of life requires constant checking in the real-universe, in order for us all to not lose sight of the fact that it was an initial, (but necessary), guess.

Colin Robinson
2012-Oct-30, 01:01 AM
I think you'll find that acetylene is all but absent in Titan's atmosphere (http://cosmoquest.org/forum/showthread.php/136925-News-from-Titan?p=2051306#post2051306) … but that's another story …

According to Table 4 in this paper by K. Didriche and others (http://www.chem.hawaii.edu/Bil301/BOAtitan2011/KeevinDidriche.pdf), based on data from Cassini, the level of acetylene in Titan's stratosphere is about 4 x10-6, i.e. 4 parts per million.

According to these figures, acetylene is in fact the 3rd commonest carbon compound in that region of Titan's atmosphere, after methane 1.6 x10-2 and ethane (around 1.5 x 10-5).

headrush
2012-Oct-30, 06:15 AM
You identify it when you discover it, not before. However you cannot identify something as a kind of something if you don't have a prior definition or concept of that kind of something. In this case the kind of thing is life, but we cannot identify other instances of life if we don't already have a definition or concept of what life is.

Yes, I agree. But in the post snippets I quoted, You disagreed with Selfsim, when you actually should have agreed. Any definition of life you come up with has no meaning if you only have a sample size of one. When and if we discover ET life, it may share some characteristics or it may not, we don't know until then. Will your definition have meaning if we don't find anything that matches your criteria ? Or will you then say, "my definition has meaning, but not in this case" ?

Paul Wally
2012-Oct-30, 10:17 AM
Any definition of life you come up with has no meaning if you only have a sample size of one.

A definition is not an hypothesis, it has nothing to do with sample size, nor is the kind of thing that awaits empirical confirmation. It's more a matter of usefulness, as Colin mentioned earlier about the usefulness of different definitions for acidity/basicity. I'm also not sure whether a definition is the kind of thing that is capable of being meaningless, because the very purpose of a definition is to tell us the meaning of a word or how we should use the word.


When and if we discover ET life ... How would we apply the word "life" in that case without having a prior definition of life?


...it may share some characteristics or it may not
The "it" would be some interesting phenomenon, not yet classified as "life" according to our definition of life. The phenomenon must first be investigated to determine whether it is life, according to our definition of life.


... we don't know until then.

We don't know what phenomenon we're going to discover. We may initially find that the phenomenon is some interesting form of complex self-organization, and the scientific investigation could be to understand how that form of complex self-organization relates to the more particular form of self-organization that we call life. Depending on the outcome of such a detailed investigation, we might decide to call the phenomenon something other than life or we might decide to extend the definition of life to include that as an instance. With such a broader definition of life we would then have two instances of life; Earth-life and whatever that other phenomenon is.


Will your definition have meaning if we don't find anything that matches your criteria ? Or will you then say, "my definition has meaning, but not in this case" ?

My definition, or any other definition of life for that matter, will still have meaning. It will just not have the same meaning as a different definition.

MarianoRF
2012-Oct-30, 10:59 AM
According to Table 4 in this paper by K. Didriche and others (http://www.chem.hawaii.edu/Bil301/BOAtitan2011/KeevinDidriche.pdf), based on data from Cassini, the level of acetylene in Titan's stratosphere is about 4 x10-6, i.e. 4 parts per million.

According to these figures, acetylene is in fact the 3rd commonest carbon compound in that region of Titan's atmosphere, after methane 1.6 x10-2 and ethane (around 1.5 x 10-5).

What kind of life do you imagine? I mean, bacterial life? or maybe a complex organism?

Colin Robinson
2012-Oct-30, 12:15 PM
What kind of life do you imagine? I mean, bacterial life? or maybe a complex organism?

I wouldn't expect active complex organisms like animals on Titan, because I don't think that the energy sources available would be enough for them. I would think more in terms of populations of microbes, or conceivably something larger but like a fungus — an organism large enough to see, but which stays in one place rather than running about.

eburacum45
2012-Oct-30, 01:42 PM
The "it" would be some interesting phenomenon, not yet classified as "life" according to our definition of life. The phenomenon must first be investigated to determine whether it is life, according to our definition of life.
Absolutely. The most common form of self-replicating phenomenon in the universe might be a series of artificial, automated factories of unknown design, collecting materials and reproducing new factories and dispersing them to new locations. Such a collection of factories would seem to fit many definitions of 'life'; but factories of this sort might not contain many biochemical molecules at all- the factories could be mostly made of inorganic materials instead. I would guess that our civilisation would be able to make such factories reasonably soon - in the next thousand years, perhaps- and potentially release them to spread throughout the galaxy. Probably replicating factories of this sort would contain some, or many biological features - but they could also be extremely different from any biological life that we know.

Would this sort of mechanical replicating system be classed as life, and could we detect it if it were on Titan?
If such an artificial self-replicating system were designed to be particularly subtle and stealthy, we might not even detect it on Earth.

MarianoRF
2012-Oct-30, 01:43 PM
I wouldn't expect active complex organisms like animals on Titan, because I don't think that the energy sources available would be enough for them. I would think more in terms of populations of microbes, or conceivably something larger but like a fungus — an organism large enough to see, but which stays in one place rather than running about.

Yeah, but the temperature in the surface of Titan is about -170 C... too cold to sustain a fungus.
And what is really even stranger, is that Titan has oceans, rivers and lake in liquid state, even with that extremely cold temperature.

eburacum45
2012-Oct-30, 06:15 PM
Indeed, but they are not lakes of water. They are probably hydrocarbons of some sort; possibly quite thick and gooey.

Selfsim
2012-Oct-30, 07:35 PM
I'm glad you agree that my enquiry is legitimate.

Developing a new life-form in a lab would require very intricate nano-technology. However, the way scientists discuss this question is already grounded in laboratory experiments with different solvents.

There is a chapter about solvents in the report by Baross and others on Limits of Organic Life in Planetary Systems. (http://www.nap.edu/openbook.php?record_id=11919&page=69) Both methane and sulfuric acid are among the solvents discussed. (I know I've mentioned this publication before in related threads.)Sure ... read it again this time 'round as well. This quote from page #74 is an interesting one...

Thus the environment of Titan meets the absolute requirements for life. Titan is not at thermodynamic equilibrium. It has abundant carbon-containing molecules and heteroatoms and a fluid environment. Titan’s temperature is low enough to permit a wide range of bonding, covalent and noncovalent. Titan undoubtedly offers other resources believed to be useful for catalysis necessary for life, including metals and surfaces.

This makes inescapable the conclusion that if life is an intrinsic property of chemical reactivity, life should exist on Titan. Indeed, for life not to exist on Titan, we would have to argue that life is not an intrinsic property of the reactivity of carbon-containing molecules under conditions where they are stable. Rather, we would have to conclude that either life is scarce in these conditions or that there is something special, and better, about the environment that Earth presents (including its water)I like the commitment ...given the statement they made on page #72:

hypothetical reactions that exploit a C=N unit in ammonia can be proposed in analogy to the metabolic biochemistry that exploits the C=O unit in terran metabolism in water (Figure 6.1).6 Given this adjustment, metabolism in liquid ammonia is easily conceivable.… All subject to the initial hypothetical analogy where they imagine that such a reaction actually occurs. The only way this could be valid in the real universe, is for there to be evidence of it … ie: it has to be discovered, (or invented).

So if their definition of life isn't found on Titan, then your whole organic-chemistry-in-a-complex-environment-results-in-life story comes to an end?? :clap: (Couldn't resist it … :) )

Now that's what I call a balanced hypothesis!


What do you mean by a "balanced hypothesis"? .. and you're asking me?
Why not ask one of the professional 'hypothesicists'/speculators around here? I'd like to see their version of one! (I haven't seen one yet).

Selfsim
2012-Oct-30, 07:47 PM
Indeed, but they are not lakes of water. They are probably hydrocarbons of some sort; possibly quite thick and gooey.If there's no liquid water*, then any 'life' is purely based on a hypothetical (imagined) instance of a theoretically conceivable chemical reaction .. which would be made feasible by a very particular environment .. and then everything from thereon would somehow miraculously follow the same evolutionary principles and metabolic pathways as life on Earth. Would you call that 'plausible'?

*There are those who have hypothesised that Titan's sub-surface is a eutectic mixture of frozen ammonia, water and rocky stuff anyway. This is based on remote spatial dimension measurements however, (density, orbital/other physical dimensional characteristics, etc). That is: not definitive spectroscopic measurements.

eburacum45
2012-Oct-30, 09:05 PM
If such an alternative biochemistry were possible, then it would presumably have entirely different but possibly analogous metabolic pathways that have evolved independently. Evolution is a process that could happen in the absence of the biochemistry we are familiar with; it is the survival of the fittest, or rather the survival of the survivors- (a tautological, but real and effective process nevertheless) and it could happen in the absence of DNA or ATP.

For instance a form of evolution can be modelled in a computer - such things as evolutionary algorithms display an optimizing behaviour over time. Could such an optimizing evolution emerge on Titan? Perhaps. Would we recognise the results if they were very differnt to Earth biochemistry? I think so - but it might take close and detailed examination of the evidence, preferably on the spot.

headrush
2012-Oct-30, 09:18 PM
A definition is not an hypothesis, it has nothing to do with sample size, nor is the kind of thing that awaits empirical confirmation. It's more a matter of usefulness, as Colin mentioned earlier about the usefulness of different definitions for acidity/basicity. I'm also not sure whether a definition is the kind of thing that is capable of being meaningless, because the very purpose of a definition is to tell us the meaning of a word or how we should use the word.
I almost agreed with your first *statement. Empirical confirmation is surely how you arrive at a definition ? Usefulness is directly related to how accurate the definition is.
A definition is meaningless if it is not definitive. And you then say that words have to be useful ! How about sticking to the meaning of definition ?


How would we apply the word "life" in that case without having a prior definition of life? Exactly.
We could only speculate (and test everything) or we could assume some earthlike aspects. Either way, we cannot expect an earth-based definition to be entirely accurate. i.e. not a definition. I agree we are capable of thinking outside the box, BUT ...
as Selfsim said, it has no meaning until be actually bring conjecture into reality. It's just conjecture, not definition, not recognition of definition.
Please let's all use the same words, or it all gets needlessly complicated. (This is not my definition of definition BTW, if that's not too sickly).



The "it" would be some interesting phenomenon, not yet classified as "life" according to our definition of life. The phenomenon must first be investigated to determine whether it is life, according to our definition of life.



We don't know what phenomenon we're going to discover. We may initially find that the phenomenon is some interesting form of complex self-organization, and the scientific investigation could be to understand how that form of complex self-organization relates to the more particular form of self-organization that we call life. Depending on the outcome of such a detailed investigation, we might decide to call the phenomenon something other than life or we might decide to extend the definition of life to include that as an instance. With such a broader definition of life we would then have two instances of life; Earth-life and whatever that other phenomenon is.



My definition, or any other definition of life for that matter, will still have meaning. It will just not have the same meaning as a different definition.
More of the same it appears.
Sorry.

Selfsim
2012-Oct-30, 09:30 PM
If such an alternative biochemistry were possible, then it would presumably have entirely different but possibly analogous metabolic pathways that have evolved independently. Evolution is a process that could happen in the absence of the biochemistry we are familiar with; it is the survival of the fittest, or rather the survival of the survivors- (a tautological, but real and effective process nevertheless) and it could happen in the absence of DNA or ATP.For instance a form of evolution can be modelled in a computer - such things as evolutionary algorithms display an optimizing behaviour over time. Could such an optimizing evolution emerge on Titan? PerhapsAll of what you say, is only made 'possible' because of the hypothetical definition of your alternative biochemistry, applied in the first place. None of it is real .. its all made up, right?

The 'Evolution computer modelling', (of which you speak), is based on the definition of the 'alternative biochemistry' which is intrinsically defined as behaving in this very way in the first place. This is circularity in its finest form. The model preserves the integrity of the initial definition (or posit). The 'computer simulation' is meaningless … (ie: "hypothesis in, hypothesis out")

I do apologise, (if this offends) .. but I simply cannot see how what you've said makes any difference whatsoever, to anything which can progress science.

headrush
2012-Oct-30, 09:38 PM
I should add to my last post that I am interested in how we would test and/or detect ET life. But we have to know what our own, known characteristics are first. And that necessarily leads on to the definition of "earthlike" which is where, I believe, we started this digression.
Personally, I don't know if life on Titan would be detectable, earthlike or not. What are we looking for ?

It appears to me that we are looking for exothermic reactions. Chemicals can organise themselves, crystallize etc, but a chemical reaction that engenders another reaction which is of "use" to the first would seem to indicate some form of life.
In our experience, this is usually accompanied by energy hoarding and/or consumption, creating an imbalance of energy, which can then be detected.

It's a bit too soon to be counting toes :)

Paul Wally
2012-Oct-30, 09:50 PM
I almost agreed with your first *statement. Empirical confirmation is surely how you arrive at a definition ?

That's my whole point. A definition doesn't require confirmation. We can formulate a very accurate definition of the concept of a Dyson sphere, but that wouldn't be an assertion that Dyson sphere's exist. Even if Dyson spheres don't exist, that doesn't make the definition any less meaningful. The existence or non-existence of something in the actual physical universe has nothing to do with it's definition. A definition only says what a word means, not that what it means actually exists. Many things are defined before they exist, like engineering artifacts for example.

headrush
2012-Oct-30, 09:59 PM
That's my whole point. A definition doesn't require confirmation. We can formulate a very accurate definition of the concept of a Dyson sphere, but that wouldn't be an assertion that Dyson sphere's exist. Even if Dyson spheres don't exist, that doesn't make the definition any less meaningful. The existence or non-existence of something in the actual physical universe has nothing to do with it's definition. A definition only says what a word means, not that what it means actually exists. Many things are defined before they exist, like an engineering concept.
It appears we are using different definitions then. This isn't just engineering or design, this is the basis of all science. We define hydrogen as having Atomic number 1; atomic weight 1.00794; melting point -259.14°C; boiling point -252.8°C; density at 0°C 0.08987 gram per liter; valence 1.

Should we now accept a different definition or use a different word for definition ?

ETA. I'm not prepared to debate this distraction any longer. Just be aware that when I say definition in future, I'm referring to something that has actually been defined by experiment and experience, not presupposed and "taken as read".

eburacum45
2012-Oct-30, 10:05 PM
I simply cannot see how what you've said makes any difference whatsoever, to anything which can progress science.
And I fully understand your point. Nevertheless the possibility remains that a completely novel biochemistry has evolved on Titan, and it would be completely unfamiliar to us. How could an 'astrobiologist' design an instrument package to test for the unknown?

One way would be to search for self-replicating closed metabolic systems that might occur in the environment on Titan. This might be difficult today, but over time research into novel self-replicating systems could reveal a large number of different options for such systems in a range of different environments. Here for example is research into alternatives to DNA;
http://www.newscientist.com/article/dn21720-move-over-dna-six-new-molecules-can-carry-genes.html

The remarkable commercial potential of self-replicating systems could easily drive such research in the coming decades and centuries; so that, by the time we are ready to look for non-terrestrial biochemistries, we will have a fairly wide range of different options to choose from. I would expect that very little of this research and development will be carried out by 'astrobiologists'; most of it will probably be achieved by chemists working on industrial applications. But if and when we ever find any 'exolife', the subject of self-replicating systems will probably be much better understood.

Colin Robinson
2012-Oct-30, 10:38 PM
hypothetical reactions that exploit a C=N unit in ammonia can be proposed in analogy to the metabolic biochemistry that exploits the C=O unit in terran metabolism in water (Figure 6.1).6 Given this adjustment, metabolism in liquid ammonia is easily conceivable.… All subject to the initial hypothetical analogy where they imagine that such a reaction actually occurs. The only way this could be valid in the real universe, is for there to be evidence of it … ie: it has to be discovered, (or invented).

What is hypothetical here is not the C=N unit itself, it is well known to chemists, although it is not stable in an aqueous solution. It's true that we don't yet have an example of a biochemical system using C=N instead of C=O. Why would we have an example, when we haven't yet explored a non-aqueous environment where C=N units would be stable?


This quote from page #74 is an interesting one...

Thus the environment of Titan meets the absolute requirements for life. Titan is not at thermodynamic equilibrium. It has abundant carbon-containing molecules and heteroatoms and a fluid environment. Titan’s temperature is low enough to permit a wide range of bonding, covalent and noncovalent. Titan undoubtedly offers other resources believed to be useful for catalysis necessary for life, including metals and surfaces.

This makes inescapable the conclusion that if life is an intrinsic property of chemical reactivity, life should exist on Titan. Indeed, for life not to exist on Titan, we would have to argue that life is not an intrinsic property of the reactivity of carbon-containing molecules under conditions where they are stable. Rather, we would have to conclude that either life is scarce in these conditions or that there is something special, and better, about the environment that Earth presents (including its water)

So if their definition of life isn't found on Titan, then your whole organic-chemistry-in-a-complex-environment-results-in-life story comes to an end?? :clap: (Couldn't resist it … :) )

I'm glad you underlined those sentences, and I agree in a way with your comment, although I don't quite see what you find so funny about it.

It seems to me that the sentence you've underlined is an excellent example of a proposition which is falsifiable, and is intended to be falsifiable. The proposition is that life emerges wherever carbon-containing molecules are stable and chemically active. If life does not exist on Titan, then the proposition is false.

In short...

Thorough study of Titan may, quite conceivably, demonstrate that a complex organic chemistry does NOT always result in life. In that case, it will be interesting to see in detail which a chemically active but non-living planet-sized environment is actually like.


Now that's what I call a balanced hypothesis!

Yes, I'd agree!

Paul Wally
2012-Oct-30, 10:41 PM
It appears we are using different definitions then. This isn't engineering or design, this is science. We define hydrogen as having Atomic number 1; atomic weight 1.00794; melting point -259.14°C; boiling point -252.8°C; density at 0°C 0.08987 gram per liter; valence 1.

We're using the same concept of definition. You just don't to see the similarity. That definition of hydrogen tells us what we must observe if we are to call it "hydrogen", just as a definition of life tells us what we must observe if we are to call it life.

Selfsim
2012-Oct-30, 10:42 PM
How could an 'astrobiologist' design an instrument package to test for the unknown?Well, I'd say for starters keep the design away from someone who already thinks they understand life or alternative chemistries which they think might lead to 'life'. (I think this covers most of 'Astrobiology?)

One considred aspect which I've heard Steven Squyres come up with (roughly transcribed) was that the complexity of the task at hand is proportional to the sophistication of the 'instrument' package. It could well be that human exploration, (armed with all the latest gizmos), might be the only way we could detect life, if it was present, someplace other than Earth. In lieu of that, extending our senses robotically (which is basically what probes are all about) probably optimises the 'chances' of detection (of 'something'). Actually confirming such a find however, (in the real universe), in order that it may then have some meaning, would require 'hands-on testing .. (for exactly the same set of complexity driven reasons). This would translate to return sample (less preferred), or onsite biological testing.
This would only make sense if the discovery loosely mimics our own life functions. Over-engineering things in advance of such a detection (of a 'something' … which seems to be the gist of what's being suggested here, is just that .. over-engineering based on heresay).


One way would be to search for self-replicating closed metabolic systems that might occur in the environment on Titan. This might be difficult today, but over time research into novel self-replicating systems could reveal a large number of different options for such systems in a range of different environments. Here for example is research into alternatives to DNA;
http://www.newscientist.com/article/dn21720-move-over-dna-six-new-molecules-can-carry-genes.htmlWill have a read, (and comment), when I get the chance .. (thanks for the reference).


The remarkable commercial potential of self-replicating systems could easily drive such research in the coming decades and centuries; so that, by the time we are ready to look for non-terrestrial biochemistries, we will have a fairly wide range of different options to choose from. I would expect that very little of this research and development will be carried out by 'astrobiologists'; most of it will probably be achieved by chemists working on industrial applications. But if and when we ever find any 'exolife', the subject of self-replicating systems will probably be much better understood. .. but not able to be generalised beyond what we already know from Earth-life.

Selfsim
2012-Oct-30, 10:53 PM
We're using the same concept of definition. You just don't to see the similarity. That definition of hydrogen tells us what we must observe if we are to call it "hydrogen", just as a definition of life tells us what we must observe if we are to call it life.In the case of say hydrogen, those are 'hard' measurements of 'hard' characteristics, whose behaviours are well understood, and which can be/have been reverified over and over again. The presence of them, and their behaviours, can be predicted because they have been measured and detected beyond Earth (and in controlled lab conditions). Their precise behaviours in 'extreme' environments beyond everyday Earth-conditions (and in our labs) may still not be fully known, however.

Life is not a single atom, a simple compound, or even a complex compound. Even its approximate measurements, still evade medical and biological sciences.

How can you draw such a loose analogy between the two examples you compare, and expect it to be accepted? (Ie: Is a virus 'life'? Is a growing crystal 'life'?)

Paul Wally
2012-Oct-30, 11:46 PM
Life is not a single atom, a simple compound, or even a complex compound.

And I didn't say life is a "single atom, a simple compound, or even a complex compound". Headrush and I were quibbling about the meaning of the word "definition". I was just illustrating that "definition" means the same in both cases, not that the two cases are the same. Anyway, how do you know that it
is "life" that is "not a single atom, a simple compound, or even a complex compound" without applying your definition of life in that case? What are your definitions of "life" and "Earth-like life". You've been conspicuously silent about your definitions of these terms and yet you use them quite liberally.


Is a virus 'life'? Is a growing crystal 'life'?)

Those depend on a definition of life. According to one definition a virus is 'life' and according to another it isn't. "Life" is a word and we define it's usage.

Selfsim
2012-Oct-31, 01:40 AM
Anyway, how do you know that it is "life" that is "not a single atom, a simple compound, or even a complex compound" without applying your definition of life in that case? What are your definitions of "life" and "Earth-like life". You've been conspicuously silent about your definitions of these terms and yet you use them quite liberally.Oh I'm quite satisfied with the 'Metabolism, Reproduction, Homeostasis, etc' definitions for Earth-life. If you're asking for my 'generalised', (your term), definition of Earth life, then that'll do for that, as well (ie: for starters).

If you're asking for a universally applicable generalised definition of 'life', then I would say: 'unknown' or 'speculative' ones have been authored.

If you're asking for a definition of 'alternative life' then I'd say: 'Check out my last crayon drawing of an alien .. after all, that's as good as any others around … ' :p :)

Paul Wally
2012-Oct-31, 02:22 AM
Oh I'm quite satisfied with the 'Metabolism, Reproduction, Homeostasis, etc' definitions for Earth-life. If you're asking for my 'generalised', (your term), definition of Earth life, then that'll do for that, as well (ie: for starters).



In other words according to your definition, if we find some reproducing organism, with a metabolism and homeostasis etc on Titan then that would be Earth-life? Or is it your claim that Earth-life (as you defined it) cannot have a different chemical basis? If indeed you're making the latter claim, then how do you know that for a fact?

Selfsim
2012-Oct-31, 03:26 AM
In other words according to your definition, if we find some reproducing organism, with a metabolism and homeostasis etc on Titan then that would be Earth-life? Or is it your claim that Earth-life (as you defined it) cannot have a different chemical basis? If indeed you're making the latter claim, then how do you know that for a fact?No. A universal, generalised definition of 'life', is presently 'unknown' or 'speculative', (basically 'undefined'). We are presently in the very early stages of attempting to test some of these speculations.

Seeing as Titan is exclusive of Earth, and yet a subset of the Universe, then whatever 'might' be there, is presently 'unknown', and would be 'speculative'.

When and if something is found there, a definition would evolve according to whatever functions it appears to exhibit, (within the limits of our sciences .. and there are lots of those). Presumably there would be something about it, which attracts our attention in the first place. Whatever that 'something' is, would be the first step in leading towards defining what it might be. It may well be unique in our present knowledge-space .. so classifying it within some type of grouping, might involve having to snoop around for other things there, which may or may not be similar in functionality. Using Earth-life life definitions to classify it, would require it to exhibit a strong degree of similarity with many Earth-life functions, and would probably also require it be a unique 'type' within that environment (variation could take it closer to, or further away from 'Earth-like' functionality … who knows?). Such a 'possibility' exists, but it would be a subset of the overall plethora of other 'possibilities', (which are not presently constrained at all, and thus presently present with equal 'weighting'). Even if it possessed such a striking degree of similarity, there may still be reasons for not lumping it together with our Earth-life functional groupings.

Attempting to classify it before it exists in reality, (ie: 'is discovered', in your language), is simply nonsensical, as its present status is 'unknown' and 'unclassifiable' .. which is a valid state for the entire issue to presently be in.

Assuming it to exist at all, is also pure imagination at work, and in no way, should be assumed to reflect physical reality in the slightest.

Selfsim
2012-Oct-31, 07:24 AM
Thorough study of Titan may, quite conceivably, demonstrate that a complex organic chemistry does NOT always result in life. In that case, it will be interesting to see in detail which a chemically active but non-living planet-sized environment is actually like.So if Titan is capable of falsifying such a hypothesis, why isn't Mars? After all, it looks like Mars once had complex chemistry with lotsa liquid water, the minerals of volcanic regions of Earth, maybe even a few rocks shared with Earth, more available energy than Titan, and probably even some C=O chemistry.

So why can't Mars be considered along the same lines?

Colin Robinson
2012-Oct-31, 09:02 AM
I've been think further about the question of acetylene levels in Titan's atmosphere. As I mentioned in post 26, it is the 3rd most abundant carbon compound, at 4 parts per million in the stratosphere.

Which is a lot less than the level of hydrogen, which is 0.1 percent, i.e. 1,000 parts per million -- a relevant comparison when you consider that hydrogen and acetylene are apparently produced by the same chemical reaction in the upper atmosphere (photolysis of methane).

One difference is this... hydrogen is a gas. Whereas on Titan, acetylene and its relatives (ethane etc), are not necessarily gases.

The melting point of acetylene at 1.27 atm is 192.4 K. Surface temperature of Titan is 93.7 K, and the surface pressure is about 1.5 atm. So acetylene tends to be a solid not a gas, at least once it finds its way to the surface.

That is why planetary scientists before 2010 expected acetylene formed in Titan's upper atmosphere to precipitate and accumulate on the ground.

On the other hand, it was predicted that if there are organisms on Titan, then acetylene would not build up on the surface, because the organisms would decompose it and thereby obtain energy...

So, before 2010, there were two models for the amount of acetylene on Titan's surface, a simple model with lots of solid acetylene, and a model complicated by the presence of organisms, resulting in much less surface acetylene.

That is the background to the much-reported findings in June 2010 — based on Strobel's work on hydrogen diffusion, and Roger Clark's study of surface hydrocarbon deposits — that something on Titan does seem to be consuming both acetylene and hydrogen...

Yes, there are a range of possible explanations... We don't know, at this time, which explanation is right... But there is definitely something to be explained there...

Paul Wally
2012-Oct-31, 12:01 PM
No. A universal, generalised definition of 'life', is presently 'unknown' or 'speculative', (basically 'undefined'). We are presently in the very early stages of attempting to test some of these speculations.

We're talking about your definition of "Earth life" now. If something satisfying your own definition of Earth life is found, then why isn't it called Earth life then?

MarianoRF
2012-Oct-31, 12:27 PM
I've been think further about the question of acetylene levels in Titan's atmosphere. As I mentioned in post 26, it is the 3rd most abundant carbon compound, at 4 parts per million in the stratosphere.

Which is a lot less than the level of hydrogen, which is 0.1 percent, i.e. 1,000 parts per million -- a relevant comparison when you consider that hydrogen and acetylene are apparently produced by the same chemical reaction in the upper atmosphere (photolysis of methane).

One difference is this... hydrogen is a gas. Whereas on Titan, acetylene and its relatives (ethane etc), are not necessarily gases.

The melting point of acetylene at 1.27 atm is 192.4 K. Surface temperature of Titan is 93.7 K, and the surface pressure is about 1.5 atm. So acetylene tends to be a solid not a gas, at least once it finds its way to the surface.

That is why planetary scientists before 2010 expected acetylene formed in Titan's upper atmosphere to precipitate and accumulate on the ground.

On the other hand, it was predicted that if there are organisms on Titan, then acetylene would not build up on the surface, because the organisms would decompose it and thereby obtain energy...

So, before 2010, there were two models for the amount of acetylene on Titan's surface, a simple model with lots of solid acetylene, and a model complicated by the presence of organisms, resulting in much less surface acetylene.

That is the background to the much-reported findings in June 2010 — based on Strobel's work on hydrogen diffusion, and Roger Clark's study of surface hydrocarbon deposits — that something on Titan does seem to be consuming both acetylene and hydrogen...

Yes, there are a range of possible explanations... We don't know, at this time, which explanation is right... But there is definitely something to be explained there...

I've read that there could be meteorological and chemical explanations to that phenomena, but also having in mind that there could be some kind of organism consuming those compounds. Whatever the truth is, it's something new for us not previously seen, and certainly, not here on Earth.

Paul Wally
2012-Oct-31, 02:54 PM
Yes, there are a range of possible explanations... We don't know, at this time, which explanation is right... But there is definitely something to be explained there...

I think in an earlier post you mentioned something about a catalyst, as a possible explanation. Are there any new developments on what such a catalyst might be?


I've read that there could be meteorological and chemical explanations to that phenomena, but also having in mind that there could be some kind of organism consuming those compounds. Whatever the truth is, it's something new for us not previously seen, and certainly, not here on Earth.

There is of course a limit to how new it is going to be for us. Since we don't live in a geocentric and an illogical universe, we can expect logical and mathematical principles of self-organizing complexity to apply on Titan as it would apply anywhere. We also don't expect the laws of physics to be suddenly violated specifically on Titan. So there are already certain not so new things that we already know with very high degree of certainty to exist on Titan, and that provides us with a basis for conjecturing specific possible explanations within the framework of what we already know.

Colin Robinson
2012-Oct-31, 07:23 PM
So if Titan is capable of falsifying such a hypothesis, why isn't Mars? After all, it looks like Mars once had complex chemistry with lotsa liquid water, the minerals of volcanic regions of Earth, maybe even a few rocks shared with Earth, more available energy than Titan, and probably even some C=O chemistry.

So why can't Mars be considered along the same lines?

Mars may once have had lotsa liquid water and plenty of available energy, but how long ago? Determining whether a planet did or did not have life billions of years in the past is a challenging task... Even if we find something that looks like a bunch of fossilized (mineralized) microbes, how to establish they really are that, and not just minerals with microbe-like shapes?

Compared to Titan today, Mars today has much less surface liquid, and Mars' atmosphere is much closer to chemical equilibrium, which means much less available chemical energy than on Titan. A range of organic compounds is known to exist on Titan, but not on Mars. Curiosity has laser-based equipment to look for organics, and it will be interesting to see whether it finds any...

Selfsim
2012-Oct-31, 07:25 PM
We're talking about your definition of "Earth life" now. No, we are talking about 'the Sciences' definition(s) of Earth-life. I don't have anything to offer other than that, (sorry to disappoint).
The problem is attempting to apply those definitions to something which doesn't yet exist in our knowledge-space, and cannot be predicted. That's not my problem ... but it may be a problem for non-Earth-lifers!
If something satisfying your own definition of Earth life is found, then why isn't it called Earth life then?I thought I'd made that clear ..??… We won't know that, until that 'something' is discovered (and analysed)!

Selfsim
2012-Oct-31, 07:46 PM
Mars may once have had lotsa liquid water and plenty of available energy, but how long ago? Determining whether a planet did or did not have life billions of years in the past is a challenging task... Even if we find something that looks like a bunch of fossilized (mineralized) microbes, how to establish they really are that, and not just minerals with microbe-like shapes?Well, in keeping with the theme(s) I have established in this thread, that would depend on what is found (and its characteristics).


Compared to Titan today, Mars today has much less surface liquid, and Mars' atmosphere is much closer to chemical equilibrium, which means much less available chemical energy than on Titan. A range of organic compounds is known to exist on Titan, but not on Mars. Curiosity has laser-based equipment to look for organics, and it will be interesting to see whether it finds any...So, your answer is phrased in the present .. but the past … that would be an entirely different matter, eh? So, I come back to the original question .. why can't the scenario of the non-finding of evidence of past life on Mars, stand as evidence that: 'a once water based complex chemistry, does NOT always result in life?'

(CHON is actually present there by the way .. even now!)

So, following the same line of logic, why not? Perhaps we should ask Mr Wally to comment (ie: about the logic)?

Selfsim
2012-Oct-31, 07:47 PM
Since we don't live in a geocentric and an illogical universe, ...What does logic have to do with the state of the physical Universe????

Paul Wally
2012-Oct-31, 09:09 PM
No, we are talking about 'the Sciences' definition(s) of Earth-life.

So, "the sciences" are yet to come up with a definition of life. Why would "they" define something called "Earth-life" and not define life?



I don't have anything to offer other than that ...

Indeed.



The problem is attempting to apply those definitions to something which doesn't yet exist in our knowledge-space, and cannot be predicted. That's not my problem ... but it may be a problem for non-Earth-lifers!I thought I'd made that clear ..??… We won't know that, until that 'something' is discovered (and analysed)!

Analysed? With what definitions?


What does logic have to do with the state of the physical Universe????

The possibility of science is dependent on the comprehensibility (logical consistency) of the universe.

Paul Wally
2012-Oct-31, 09:35 PM
So, your answer is phrased in the present .. but the past … that would be an entirely different matter, eh? So, I come back to the original question .. why can't the scenario of the non-finding of evidence of past life on Mars, stand as evidence that: 'a once water based complex chemistry, does NOT always result in life?'


That would be a reasonable conclusion to draw, but only if your hypothetical scenario of non-finding of evidence actually arises. But even then, the job of rational science would be to understand why life didn't emerge in that particular case, and there might be perfectly understandable reasons why it didn't.

Colin Robinson
2012-Nov-01, 06:47 AM
I think in an earlier post you mentioned something about a catalyst, as a possible explanation.

Yes... actually, judging by the scientific literature I've seen about this, if acetylene and hydrogen are reacting to form methane near the surface of Titan, a catalyst of some description is the only possible explanation known... An explanation in terms of living things is really a variant of the catalyst explanation -- after all, living cells can only metabolize stuff because the cells contain catalytic molecules... Perhaps one definition of a living thing might be "a catalyst with attitude"!


Are there any new developments on what such a catalyst might be?

Not as far as I know... We do know of catalysts that can facilitate hydrogenation of acetylene, but not ones that are effective at Titan temperatures...


There is of course a limit to how new it is going to be for us. Since we don't live in a geocentric and an illogical universe, we can expect logical and mathematical principles of self-organizing complexity to apply on Titan as it would apply anywhere. We also don't expect the laws of physics to be suddenly violated specifically on Titan. So there are already certain not so new things that we already know with very high degree of certainty to exist on Titan, and that provides us with a basis for conjecturing specific possible explanations within the framework of what we already know.

Well said.

The hydrogenation of acetylene is an example: we don't know yet whether it's actually happening on Titan, and if so how – what sort of catalytical agent, with attitude or without? We do know that the reaction, if it happens, is an exothermic one – it releases energy, in a quantity that can be calculated.

Colin Robinson
2012-Nov-01, 07:16 AM
So, your answer is phrased in the present .. but the past … that would be an entirely different matter, eh? So, I come back to the original question .. why can't the scenario of the non-finding of evidence of past life on Mars, stand as evidence that: 'a once water based complex chemistry, does NOT always result in life?'

I did make the point that it is a challenging task determining whether a planet did or did not have life billions of years in the past.

But I'd agree that if it can be demonstrated convincingly that Mars never had life, but did have abundant water and complex chemistry, than it will be reasonable to conclude that "water based complex chemistry, does NOT always result in life?'


(CHON is actually present there by the way .. even now!)

The presence of those 4 elements is hardly the same thing as a complex chemistry...

MarianoRF
2012-Nov-01, 11:08 AM
Mars may once have had lotsa liquid water and plenty of available energy, but how long ago? Determining whether a planet did or did not have life billions of years in the past is a challenging task... Even if we find something that looks like a bunch of fossilized (mineralized) microbes, how to establish they really are that, and not just minerals with microbe-like shapes?

Compared to Titan today, Mars today has much less surface liquid, and Mars' atmosphere is much closer to chemical equilibrium, which means much less available chemical energy than on Titan. A range of organic compounds is known to exist on Titan, but not on Mars. Curiosity has laser-based equipment to look for organics, and it will be interesting to see whether it finds any...

That's the reason why I consider Titan much more interesting than Mars, from a biological point of view. Mars is a dead red desert, where an ET life-form might have existed once. Personally, I highly doubt about life on Mars, because otherwise, we would have found some kind of remains, fosils, etc... I'm not saying we have panned the whole planet, but if there was some kind of life-activity (simple or complex), there must be remains.

Regarding Titan, in several ways it's also a mystery for us. We know very little about this world, and more missions are required to explore it. Again, I can't understand NASA decisions to continue sending rovers to Mars, instead of Titan or Enceladus. Maybe, NASA has some type of evidence and knows that there is/was some kind of life activity in Mars, that's why so much interest on this planet.

iquestor
2012-Nov-01, 12:18 PM
That's the reason why I consider Titan much more interesting than Mars, from a biological point of view. Mars is a dead red desert, where an ET life-form might have existed once. Personally, I highly doubt about life on Mars, because otherwise, we would have found some kind of remains, fosils, etc... I'm not saying we have panned the whole planet, but if there was some kind of life-activity (simple or complex), there must be remains.

Regarding Titan, in several ways it's also a mystery for us. We know very little about this world, and more missions are required to explore it. Again, I can't understand NASA decisions to continue sending rovers to Mars, instead of Titan or Enceladus. Maybe, NASA has some type of evidence and knows that there is/was some kind of life activity in Mars, that's why so much interest on this planet.

I doubt Mars ever hosted large complex life that would leave easily visible fossils, and if it did, the environment on Mars where we have visited are not good places look for them. If they exist I beleive they'd be encrusted in rock or in deep caves.

I think there were and still are microbes on Mars. The most compelling evidence to me is the annual Methane releases. 90% of methane on Earth is released by living organisms, but the other 10% is volcanism and other sources. Methane is being released seasonally on Mars in several places. It will be possible to analyze the martian methane and determine if it is possibly biologic in origin. One way is whether ethane is also present. Based on a book I recently read, another is that if heavy water vapor (deuterium) is also present it is evidence it is "old water" from the depths of Mars which points to a deep biosphere, whereas regular water points to other generation sources. I can provide a link to the book if anyone is interested.
While Titan and other bodies are very enticing, Mars seems easier and closer to study. As Robert Zubrin put it in The Case For Mars, there are many scientists who beleive there is life there and who are quietly gathering evidence and building a case. This seems to be NASA's strategy with the rovers.

MaDeR
2012-Nov-01, 12:53 PM
Personally, I highly doubt about life on Mars, because otherwise, we would have found some kind of remains, fosils, etc...
You seem do not understand, how rare and chancey are fossils in general. Martian fossils, if exists, will be ever rarer (as martian biosphere, if ever existed, would be significantly smaller than Earth's biosphere) and microfossils only (multicelluar life on Mars almost certainly never existed).


I'm not saying we have panned the whole planet
Assuming there was or is life on Mars, it would be extremely improbable that we - with current state of Mars exploration - would already stumble at remains/fossils by chance.

Four rovers covering ultraminiscule amount of planet's surface is for you enough to judge that there cannot be life on Mars? Wrong, wrong, wrong.

Selfsim
2012-Nov-01, 08:41 PM
So, "the sciences" are yet to come up with a definition of life. Why would "they" define something called "Earth-life" and not define life? Because there is no physical living thing, which facilitates the distinction of anything separate from Earth-life.

The Ebola virus was unknown until it emerged from the jungle surrounding the Ebola river in vicinity of the Congo. No-one, no theory nor any impeccably flawless logic, ever predicted it!
It had to turn up in order for science to figure it out. And please, lets not get bogged down in discussing whether or not a virus is living or not .. that's not the point .. the point is that until something which impacts biology turns up, it cannot be predicted. (This is a fundamental to the biological empirical sciences, and and also constrains 'Astrobiology' areas of conjecture).

The possibility of science is dependent on the comprehensibility (logical consistency) of the universe.Metaphysics is now a branch of Science in your book, eh?

Try on: the Anthropic principle for the existence of the Universe (just for comparative purposes). It suggests that the Universe doesn't need a purpose, nor logical consistency. It simply exists, and if it were any different, we wouldn't be around to observe it. With this particular philosophical paradigm, this 'logic', which you seem to believe can somehow replace evidence's role in empirical sciences, and in which you seem to have so much faith, is our own creation … nothing more.

In my book, anyone is free to indulge in whatever philosophical perspective they like .. its their free choice to make .. but please be aware of what it represents, at least to the extent that one then doesn't blindly state that the metaphysical aspects of it, are somehow 'part of Science'.

This is a classic example of a belief being so undistinguished in the mind, as to become reality!

Colin Robinson
2012-Nov-01, 08:53 PM
I doubt Mars ever hosted large complex life that would leave easily visible fossils, and if it did, the environment on Mars where we have visited are not good places look for them. If they exist I beleive they'd be encrusted in rock or in deep caves.

I think there were and still are microbes on Mars. The most compelling evidence to me is the annual Methane releases. 90% of methane on Earth is released by living organisms, but the other 10% is volcanism and other sources. Methane is being released seasonally on Mars in several places. It will be possible to analyze the martian methane and determine if it is possibly biologic in origin. One way is whether ethane is also present. Based on a book I recently read, another is that if heavy water vapor (deuterium) is also present it is evidence it is "old water" from the depths of Mars which points to a deep biosphere, whereas regular water points to other generation sources. I can provide a link to the book if anyone is interested.
While Titan and other bodies are very enticing, Mars seems easier and closer to study. As Robert Zubrin put it in The Case For Mars, there are many scientists who beleive there is life there and who are quietly gathering evidence and building a case. This seems to be NASA's strategy with the rovers.

A recent study reported on the Universe Today website (http://www.universetoday.com/97280/could-dust-devils-create-methane-in-mars-atmosphere/) argues that methane on Mars may possibly be due to an electrostatic process in whirling dust storms.

I agree that life on Mars (past or present) is an open question... However, I think there has been something of an obsession, here on Earth, with life on Mars, which goes back to the discovery of its ice caps a century or so ago... It is not the only possible habitat for life beyond Earth in the Solar System, and it's not necessarily the most likely habitat.

Selfsim
2012-Nov-01, 08:57 PM
As Robert Zubrin put it in The Case For Mars, there are many scientists who beleive there is life there and who are quietly gathering evidence and building a case. This seems to be NASA's strategy with the rovers.Gathering evidence to verify a hypothesis?

That's not how real science works .. unless it has become corrupted in the hands of the NASA strategy you're interpreting.

(I seriously doubt that's how the real scientists driving the NASA exploration program think).

Selfsim
2012-Nov-01, 08:59 PM
Maybe, NASA has some type of evidence and knows that there is/was some kind of life activity in Mars, that's why so much interest on this planet.A conspiracy theory?
(Well, that certainly spices things up a bit!)
:)
Cheers

Selfsim
2012-Nov-01, 09:20 PM
Assuming there was or is life on Mars, it would be extremely improbable that we - with current state of Mars exploration - would already stumble at remains/fossils by chance.Why would it be 'extremely improbable', given that one of the primary driving reasons for sending Curiosity to the Gale crater region was to maximise the chances of finding past life signs in what appears to be a once habitable region?
You seem to think that the ~billion dollar Curiosity rover was sent to the wrong place to look for it, eh?


Four rovers covering ultraminiscule amount of planet's surface is for you enough to judge that there cannot be life on Mars? Wrong, wrong, wrong... and you seem to think you already know the distribution patterns of what 'might' be there, before any data is actually gathered? Wrong, wrong, wrong!

A geochemical lab being sent to a high probability region, which is capable of finding complex organics (both past and present), is capable of ruling out 'life' being distributed in a past flowing water environment, in a high probability region of the planet … That, coupled with 'no evidence' coming from the other rovers' data gatherings, and making use of the 'inference-based' paradigm under which your logic operates, is capable of making strong conclusions about a wide area of the planet … Get real .. and get consistent!

Selfsim
2012-Nov-02, 07:39 AM
Here ya go, Colin ... an article published just today ...

Cassini Halloween treat: Titan glows in the dark (http://phys.org/news/2012-11-cassini-halloween-titan-dark.html)


Scientists are interested in studying the input of energy from the sun and charged particles into Titan's atmosphere because it is at the heart of the natural organic chemistry factory that exists in Titan's atmosphere. "Scientists want to know what galvanizes the chemical reactions forming the heavy molecules that develop into Titan's thick haze of organic chemicals," said Linda Spilker, Cassini project scientist, also at JPL. "This kind of work helps us understand what kind of organic chemistry could have existed on an early Earth."
...
Scientists' best guess is that the glow is being caused by deeper-penetrating cosmic rays or by light emitted due to some kind of chemical reaction deep in the atmosphere. "This is exciting because we've never seen this at Titan before," West said. "It tells us that we don't know all there is to know about Titan and makes it even more mysterious."

So there ya go ... we are still limited in our boundaries of understanding, and there is still much to learn from the physical dynamics of other 'worlds' like Titan. We can't work it all out coming solely from a familiarity of what happens on Earth! Other complex processes exist elsewhere which may not necessarily happen on Earth.

Your questions about the supposed 'acetylene depletion' (which I still don't necessarily accept .. its more like: 'unexpectedly low levels of it'), could well be being influence in some way by this rather curious phenomenon. I also wonder what role, (if any), Saturn's magnetic field plays in all this(??)

Colin Robinson
2012-Nov-02, 08:14 AM
Here ya go, Colin ... an article published just today ...

Cassini Halloween treat: Titan glows in the dark (http://phys.org/news/2012-11-cassini-halloween-titan-dark.html)



So there ya go ... we are still limited in our boundaries of understanding, and there is still much to learn from the physical dynamics of other 'worlds' like Titan. We can't work it all out coming solely from a familiarity of what happens on Earth! Other complex processes exist elsewhere which may not necessarily happen on Earth.

Your questions about the supposed 'acetylene depletion' (which I still don't necessarily accept .. its more like: 'unexpectedly low levels of it'), could well be being influence in some way by this rather curious phenomenon. I also wonder what role, (if any), Saturn's magnetic field plays in all this(??)

Thanks for the link, it's an interesting article... It really underlines the fact that Titan is a chemically active place — a place where charged molecules (ions), as well as uncharged molecules are doing a range of complex stuff. Please do not misunderstand me — I don't know whether Titan has life or not. I don't know whether Mars has life or not either. But if I had a choice between looking for life on a chemically active moon or planet (such as Titan), or chemically inert one, i.e. one whose atmosphere is close to chemical equilibrium (such as Mars) then I would definitely choose the chemically active place.

MarianoRF
2012-Nov-02, 11:03 AM
I doubt Mars ever hosted large complex life that would leave easily visible fossils, and if it did, the environment on Mars where we have visited are not good places look for them. If they exist I beleive they'd be encrusted in rock or in deep caves.

I think there were and still are microbes on Mars. The most compelling evidence to me is the annual Methane releases. 90% of methane on Earth is released by living organisms, but the other 10% is volcanism and other sources. Methane is being released seasonally on Mars in several places. It will be possible to analyze the martian methane and determine if it is possibly biologic in origin. One way is whether ethane is also present. Based on a book I recently read, another is that if heavy water vapor (deuterium) is also present it is evidence it is "old water" from the depths of Mars which points to a deep biosphere, whereas regular water points to other generation sources. I can provide a link to the book if anyone is interested.
While Titan and other bodies are very enticing, Mars seems easier and closer to study. As Robert Zubrin put it in The Case For Mars, there are many scientists who beleive there is life there and who are quietly gathering evidence and building a case. This seems to be NASA's strategy with the rovers.

Interesting fact about the origin of methane. How could we determine the real source? I mean, how should we measure it?
Also, there's a lot popular interest in Mars, so this boosts the global "pursuit" of ET life on that planet. I agree that Mars is "easier" and "cheaper" to study than Titan, but I think a real "treasure" is waiting to be discovered in Titan.


Four rovers covering ultraminiscule amount of planet's surface is for you enough to judge that there cannot be life on Mars? Wrong, wrong, wrong.

Of course not. But due to the fact that Curiosity's state-of-the-art equipment hasn't found any real/solid evidence of past/present life in Mars, I highly doubt that there could be life-activity there. According to the latest releases, it seems that the martian soil is mainly composed by volcanic compounds, so it's fair to conclude that it's a planet that in its ancient past, had a lot of vulcan activity.


I agree that life on Mars (past or present) is an open question... However, I think there has been something of an obsession, here on Earth, with life on Mars, which goes back to the discovery of its ice caps a century or so ago... It is not the only possible habitat for life beyond Earth in the Solar System, and it's not necessarily the most likely habitat.

I agree with you. There's some kind of obsession with Mars. And certainly, it's not the only possible habitat for life beyond Earth. We have to take into account that Mars is a hostile enviornment, with extremely cold temperatures of -140°C in winter, so nothing could survive there. Titan is a little bit colder: -172°C. But according to wikipedia: "Martian surface temperatures vary from lows of about −143 °C (−225 °F) (at the winter polar caps) to highs of up to 35 °C (95 °F) (in equatorial summer)". I ask: could something live in that "comfortable" temperature?

MaDeR
2012-Nov-02, 03:19 PM
Why would it be 'extremely improbable',
I will say it in simplest possible way.
Fossils on Earth are already rare to encounter by chance.
Fossils on Mars would be ever rarer.
Microfossils makes chances of accidental discovery many order of magnitudes lower, as you cannot spot microfossil while driving by. Also, having unambigious microfossils is way harder, as ALH84001 demonstrated.
So, yes. Extremely improbable.


given that one of the primary driving reasons for sending Curiosity to the Gale crater region was to maximise the chances of finding past life signs in what appears to be a once habitable region?
Newsflash for you: Curiosity mission is to assess habitability, not to discover life. You constantly and convieniently "forget" about it. No, your weasel words "finding past life signs" does not cut it. "Habitability" != "finding past life signs".


You seem to think that the ~billion dollar Curiosity rover was sent to the wrong place to look for it, eh?
Don't put in my mouth things that I did not said.


A geochemical lab being sent to a high probability region, which is capable of finding complex organics (both past and present), is capable of ruling out 'life' being distributed in a past flowing water environment, in a high probability region of the planet … That, coupled with 'no evidence' coming from the other rovers' data gatherings, and making use of the 'inference-based' paradigm under which your logic operates, is capable of making strong conclusions about a wide area of the planet …
Question of life on Mars (or anywhere outside of Earth, really) is not question for one mission. Entire space programs (in pural) was, are and will be commited to assess this and related questions. Demanding that case have to be closed (or even make "strong conclusions") after only one more mission is utterly ludicrous.

Your criteria for successful discovery of life, hinging on results of only one mission (that is not even built to discover life!), makes sense only in mouth of someone opposed to idea of extraterrestial life due to ideological reasons. I cannot accept such biased and loaded "proposition".


Of course not.
Yet in next sentence you state...


But due to the fact that Curiosity's state-of-the-art equipment hasn't found any real/solid evidence of past/present life in Mars, I highly doubt that there could be life-activity there.
Heeere we go again...
1. Curiosity mission barely begun. Aren't you a little too eager? Nominal mission time is two years, you know. Plus additional few year of analysis and dozens of scientific articles. And this does not even count mission extension.
2. Curtiosity mission is to assess habitability, not directly discover life. Curiosity is ill-equipped to discover life.
3. Again, a few rovers aren't nearly enough to make any case for or against life. We are in long haul here - fact that is seeemingly impossible to accept by you and Selfism.


I ask: could something live in that "comfortable" temperature?
You seem to assume that Martian life, if exists, will be on surface. Wrong again. Surface is sterilized and no life as we know it could survive directly exposed to elements that exists on surface, including sun.

Paul Wally
2012-Nov-02, 04:07 PM
Because there is no physical living thing, which facilitates the distinction of anything separate from Earth-life.

Since you refuse to define what "physical living thing" means, your sentence is without meaning. Of course, if "physical living thing" means "Earth-life" then it's just a tautology.


The Ebola virus was unknown until it emerged from the jungle surrounding the Ebola river in vicinity of the Congo. No-one, no theory nor any impeccably flawless logic, ever predicted it!
It had to turn up in order for science to figure it out. And please, lets not get bogged down in discussing whether or not a virus is living or not .. that's not the point .. the point is that until something which impacts biology turns up, it cannot be predicted. (This is a fundamental to the biological empirical sciences, and and also constrains 'Astrobiology' areas of conjecture).

All that has nothing to do with the issue I'm trying to address, which is that without universally applicable definitions we cannot form conclusions as to what any empirical finding means. Without defining what "life" means, we can neither conclude "there is life" nor can we conclude "there is no life" in any particular case, because the concept of "life" would be undefined.

For example your question:
why can't the scenario of the non-finding of evidence of past life on Mars, stand as evidence that: 'a once water based complex chemistry, does NOT always result in life? is without meaning if "life" is undefined, because how would we come to a conclusion of "non-finding of evidence of past life on Mars" if we haven't defined what life means.


Metaphysics is now a branch of Science in your book, eh?

No, philosophy of science is the branch of philosophy where we try to answer non-trivial questions about what science is. But you seem to be the legislator around here declaring normative assertions as to what counts as 'part of science' and what does not, and which 'branch' should belong where.



Try on: the Anthropic principle for the existence of the Universe (just for comparative purposes). It suggests that the Universe doesn't need a purpose, nor logical consistency. It simply exists, and if it were any different, we wouldn't be around to observe it. With this particular philosophical paradigm, this 'logic', which you seem to believe can somehow replace evidence's role in empirical sciences, and in which you seem to have so much faith, is our own creation … nothing more.

We must also be careful not to use any particular 'philosophical paradigms' like the Anthropic principle, many-universes hypothesis or unverifiable notions like your absolute unpredictability to declare a priori limits to scientific inquiry. Saying for instance that the universe is the way it is because that's the way it is implies we shouldn't bother looking for an explanation because there isn't any.

Yes, I consider logico-mathematical truths to be knowledge of a much more certain kind than empirically derived knowledge, but that doesn't mean that the former can replace the latter. The rational and the empirical I consider to be complementary aspects of science, and both are needed.



In my book, anyone is free to indulge in whatever philosophical perspective they like .. its their free choice to make .. but please be aware of what it represents, at least to the extent that one then doesn't blindly state that the metaphysical aspects of it, are somehow 'part of Science'.

This is a classic example of a belief being so undistinguished in the mind, as to become reality!

Yes, and please do try to develop an awareness of your own peculiar philosophical perspective on science. Check for instance whether you can distinguish (in your mind that is) the difference between "evidence" and "reality", and also the difference between "definition" and "hypothesis".

Good day

MarianoRF
2012-Nov-04, 02:55 PM
Curiosity mission is to assess habitability, not to discover life.

Correct, but in the end, the goal is to discover the possibility of past/present life.

MaDeR
2012-Nov-04, 10:35 PM
Correct, but in the end, the goal is to discover the possibility of past/present life.
Still does not change fact that we are decades away from declaring that life most probably do not exist on Mars. It is very hard to prove negative, fortunately we do not need to check every nook and cranny around entire planet. Case for martian life would be severely weaken if these things happened:
- Explanation for methane without involving biology and covering all observed properties, like extremely fast (in comparison to current models) vanishing and both spatial and temporal patchiness.
- Deep samples from tens of meters underground not having life nor remains/microfossils/whatever. Same results from multiple sampling sites all over planet in methane hotspots and fulfilling other conditions to maximize chances would be especially damning.

While single thing like this (methane explanation or one site yelding null result) would not be that dramatic, all of them at once would make me revise chances of current and extnict Martian life to "low to very low".

MarianoRF
2012-Nov-05, 10:30 AM
Still does not change fact that we are decades away from declaring that life most probably do not exist on Mars. It is very hard to prove negative, fortunately we do not need to check every nook and cranny around entire planet.

I think Mars has no present life, the environment is hostile and nothing could survive there. As somebody said, maybe something is living in deep caverns... but can we dig in? it's completely out of our present capabilities. I think this possibility doesn't apply to Mars. I see this planet as a big and dead desert.

Back on track, Titan is more likely to harbor some kind of bacteriological life. But it's entirely hypothetical, there are some explanations to describe the strange chemical reactions that take place there. Briefing, more missions are required to Titan.