Alien life and probability

[mr3000]

It seems to me that if life started on earth exactly once in 4.5 billion years, then it is an extremely improbable event that is a very rare if not unique occurrence in the universe. I’m aware that the number of planets in the universe, including interstellar and intergalactic planets, is an absurdly high number. However, is it possible that abiogenesis is even more unlikely than the amount of places where it could occur? Could the answer to the Fermi paradox be that life is confined to earth?

 

[256bits]

https://en.wikipedia.org/wiki/Fermi_paradox
"The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence."

Where anyone gets "the high likelihood of its existence" - advanced extraterrestrial life - is out to lunch.

Could the answer to the Fermi paradox be that life is confined to earth?

Could be. We just don't know. We do not even know the actual conditions necessary for abiogenesis (but once formed it, life, seems persistent ), let alone the conditions necessary for advanced civilizations, let alone if space travel ( even if imaginative as being the next step ) would pan out.

As the Wiki states in the reasoning " Since many of the Sun-like stars are billions of years older than the Sun, the Earth should have already been visited by extraterrestrial civilizations, or at least their probes". But such wishful thinking isn't based in anything but wishful thinking. ( Wishful in that the space explorers are benign, much like earth explorers to far off lands are benign in hindsight of the settlers ).

I would say that your hypothesis is as good as that anyone else may give.
Until it is proven false by another data point of existent life being found.

 

[PeroK]

It seems to me that if life started on earth exactly once in 4.5 billion years, then it is an extremely improbable event that is a very rare if not unique occurrence in the universe. I’m aware that the number of planets in the universe, including interstellar and intergalactic planets, is an absurdly high number. However, is it possible that abiogenesis is even more unlikely than the amount of places where it could occur? Could the answer to the Fermi paradox be that life is confined to earth?

Yes, that's possible. Professor David Kipling has some lectures and videos on this. For example:

 

[javisot]

It seems to me that if life started on earth exactly once in 4.5 billion years, then it is an extremely improbable event that is a very rare if not unique occurrence in the universe. I’m aware that the number of planets in the universe, including interstellar and intergalactic planets, is an absurdly high number. However, is it possible that abiogenesis is even more unlikely than the amount of places where it could occur? Could the answer to the Fermi paradox be that life is confined to earth?

It is a difficult question to answer; abiogenesis is the synthesis of life from inert matter, but we do not know any mechanism of abiogenesis.

The same applies to the term panspermia; it doesn't refer to a specific mechanism but rather any mechanism by which life could propagate. It's very difficult to answer your questions precisely without knowing the exact possible mechanisms, whether for abiogenesis or panspermia.

 

[pinball1970]

but we do not know any mechanism of abiogenesis.

That is not entirely correct. We do not know how life on earth began specifically but there a few ways that this could have got going. RNA world, Deep sea vents for example.

https://www.nature.com/articles/s41580-022-00514-6

https://biologyinsights.com/hydrothermal-vents-the-origin-of-life-on-earth/

 

[berkeman]

if life started on earth exactly once in 4.5 billion years,

Where do you get that from? It's more like life arose in many places on Earth at the same time after enough time had passed for several processes to take place. Think green slime mold all over the place to start things off...

EDIT -- green slime mold implies photosynthesis, which occurred later in the biogenesis process. So instead, think bland gunk accumulating around thermal vents on the ocean floors...

 

[PeroK]

Where do you get that from? It's more like life arose in many places on Earth at the same time after enough time had passed for several processes to take place. Think green slime mold all over the place to start things off...

It's possible that all life on Earth is descended from a common ancestor. Although, it may have arisen several times. You could start here:

https://en.wikipedia.org/wiki/History_of_life

 

[mr3000]

It's possible that all life on Earth is descended from a common ancestor. Although, it may have arisen several times. You could start here:

https://en.wikipedia.org/wiki/History_of_life

https://en.wikipedia.org/wiki/Last_universal_common_ancestor

 

[javisot]

That is not entirely correct. We do not know how life on earth began specifically but there a few ways that this could have got going. RNA world, Deep sea vents for example.

https://www.nature.com/articles/s41580-022-00514-6

https://biologyinsights.com/hydrothermal-vents-the-origin-of-life-on-earth/

Yes, the iron-sulfur world hypothesis, the RNA hypothesis, the RNA-peptide world hypothesis, etc, are several proposals for abiogenesis, none of which have been proven and confirmed. But I repeat, since what I said is literally correct, the term abiogenesis does not specify any particular mechanism; it refers generally to any mechanism that produces life from inert matter.

You cannot accurately answer the question "how probable is abiogenesis?" without specifying any mechanism of abiogenesis.

 

[russ_watters]

Where do you get that from? It's more like life arose in many places on Earth at the same time after enough time had passed for several processes to take place. Think green slime mold all over the place to start things off...

It also happened very early in Earth's habitable time (it just took a long time for complex life to evolve).

 

[DaveC426913]

life started on earth exactly once in 4.5 billion years, then it is an extremely improbable event that is a very rare if not unique occurrence in the universe

https://en.wikipedia.org/wiki/Last_universal_common_ancestor

I think there a few assumptions and misconceptions happening here, and trying to project it onto Fermi's Paradox is making it worse.

The idea that "life started on Earth exactly once in 4.5Gy" is being misused to suggest a bunch of unwarranted conclusions.

Not the least of which, it appears to assume that, once life arose once, it could arise another time. I tihnk that's unwarranted.

1. Once life arose, it almost certainly monopolized resources and outcompeted any other instances.
2. We don't now if life arose more than once, all we know is that only one strain survived in our records.


On the contrary, what's really interesting to think about is how soon life arose after the planet was cool enough. The blink of an eye in astronomical terms. This suggests that life is very likely to crop up almost anywhere and anytime the conditions are right.



"Although the timing of the LUCA cannot be definitively constrained, most studies suggest that the LUCA existed by 3.5 billion years ago, and possibly as early as 4.3 billion years ago"
https://en.wikipedia.org/wiki/Last_universal_common_ancestor

Earth's surface began cooling from a molten state almost immediately after its formation, with solid crust and liquid oceans potentially appearing as early as 4.4 to 4.3 billion years ago.
https://www.google.com/search?q=how+old+was+earths+surface+cool

In other words, our windows for when Earth was first fit for life, and when our LUCA lived actually overlap.

 

[PeroK]

I think there a few assumptions and misconceptions happening here, and trying to project it onto Fermi's Paradox is making it worse.

The idea that "life started on Earth exactly once in 4.5Gy" is being misused to suggest a bunch of unwarranted conclusions.

Not the least of which, it appears to assume that, once life arose once, it could arise another time. I tihnk that's unwarranted.

1. Once life arose, it almost certainly monopolized resources and outcompeted any other instances.
2. We don't now if life arose more than once, all we know is that only one strain survived in our records.


On the contrary, what's really interesting to think about is how soon life arose after the planet was cool enough. The blink of an eye in astronomical terms. This suggests that life is very likely to crop up almost anywhere and anytime the conditions are right.



"Although the timing of the LUCA cannot be definitively constrained, most studies suggest that the LUCA existed by 3.5 billion years ago, and possibly as early as 4.3 billion years ago"
https://en.wikipedia.org/wiki/Last_universal_common_ancestor

Earth's surface began cooling from a molten state almost immediately after its formation, with solid crust and liquid oceans potentially appearing as early as 4.4 to 4.3 billion years ago.
https://www.google.com/search?q=how+old+was+earths+surface+cool

In other words, our windows for when Earth was first fit for life, and when our LUCA lived actually overlap.

The real problem is that if you think there must be numerous advanced civilizations in the Milky Way, then how many are there (approximately)? The answer is that we have no idea and we may be the only one.

That life evolved early on Earth is still a single data point. You cannot conclude from that how likely it is that eventually complex life and advanced civilizations evolve. You also do not know how lucky we have been with mass extinction events.

It's all just statistical arm-waving.

 

[phyzguy]

The thing to remember is that, if new life formed today on Earth, it would get eaten very quickly. So you can't conclude that life only formed once on Earth.

 

[Ibix]

It's all just statistical arm-waving.

Exactly. That life appeared quite quickly on Earth could mean that it's really easy (as Dave and phyzguy say, abiogenesis could happen every other week and simply get ploughed under by the far more complex and robust organisms currently stomping around the place) or it could mean we're the guys who won the lottery the first week it ran. Without other data points, we don't know.

The Fermi paradox is perhaps evidence pointing towards "we got lucky", but it could also be that life is common but not nuking/greenhousing yourself into oblivion before colonising the galaxy is a lot tougher than we imagine. The square/cube law is pretty brutal for galactic colonisers, too.

 

[PeroK]

The thing to remember is that, if new life formed today on Earth, it would get eaten very quickly. So you can't conclude that life only formed once on Earth.

That sounds like a personal theory to me!

 

[javisot]

That sounds like a personal theory to me!

I understand that this is a reasonable conclusion given that we have no direct evidence of new abiogenesis processes. (The lack of evidence forces us to assume that if new abiogenesis processes exist, they are not successful)

 

[Borek]

discrepancy between the lack of conclusive evidence

(emphasis mine)

Yes, we haven't seen anything that can't be explained as a natural process (there are some strange observations, but they are random and inconclusive) - but how much have we seen?

Can be that the advanced life is quite common, as opposed to intelligence capable of producing technology.

So many ways in which this paradox can be not a paradox at all.

 

[PeroK]

In a more general context, a golden rule of using probability theory is that you understand the sample space. In this case, we simply do not understand the sample space.

 

[Ken Fabian]

Seems dependent on a big enough 'soup' and a long enough time -


My own take on the odds of life originating by chance alone is to look at the scales of things -


1.3 billion cubic kilometres of liquid water (on Earth ie one planet, that has a lot of precursor chemicals in it.)

= 1,300,000,000,000,000,000,000,000 ml

About 1,000,000 bacteria per ml live in sea water, so if the chemical precursors for those are present in primordial sea water we get enough to make...

= 1,300,000,000,000,000,000,000,000,000,000 bacteria's worth.
Give it 500 million years of chemical reactions that happen at much faster than 1 per second per ml rates - I'll be very conservative and say only 1 reaction per second (and note that life existed for several billion years before bacteria evolved...)

= 15,750,000,000,000,000 seconds x 1,300,000,000,000,000,000,000,000,000,000 bacteria's worth

= 20,475,000,000,000,000,000,000,000,000,000,000,000,000,000,000 opportunities for random chemistry + selection make the appropriate complex chemistry for earliest ‘simple’ life. Which can be expected to multiply and spread quite rapidly once a reproductively successful form (that has no predators) emerges.

Now this isn't intended to be definitive by any means - add or subtract a few zeros if that makes you happier. It is just an admittedly crude attempt to see how "very unlikely" fits with extremely large numbers of opportunities for "unlikely" to happen.

I suspect we will identify the essential chemical pathways amongst the possible pathways within mixtures of the kinds of chemicals we could expect to occur naturally without biology and under the conditions we expect to have existed - by modeling rather than experiment.

The range of conditions will be quite large too (a planet is big and varied) - different minerals washing in from land, from hydro thermal vents, from meteorite impacts and at some times, meteorite impacts in shallow water over the top of hydro thermal vents in places where unusual minerals exist. Resultant chemicals will be carried vast distances - globally for a global ocean - mixing with different ones, at different temperatures. Concentrated in tidal pools by evaporation, struck with lightning, by sparks of static electricity. Concentrated by freezing. Returned to the soup, mixed and transported again and again.

Seems like NOT evolving life given so many opportunities would be unusual and exceptional.

 

[DaveC426913]

There are, by the way, replicative cycles in nature that are far, far simpler than DNA/RNA.

The Krebs cycle (AKA citric acid cycle) is one.

I am not suggesting the Krebs cycle can be a precursor to life, simply noting that such replications do happen naturally.

Combining, that with the tendency for lipids to stick together and form enclosed bubbles where elements of the primordial soup might plausibly get concentrated (i.e. before being washed away by currents), I can see a path to more complex forms of pre-life replication.

 

[javisot]

https://en.wikipedia.org/wiki/Virus, in origins, Co-evolution hypothesis-" This is also called the "virus-first hypothesis"[27]: 24  and proposes that viruses may have evolved from complex molecules of protein and nucleic acid at the same time that cells first appeared on Earth and would have been dependent on cellular life for billions of years."

 

[BillTre]

The Fermi paradox is specifically about advanced life able to make contact with us. This is different from the origin of life, but life originating (once at least) is a condition that enables any higher life forms.

This is how I think about this group of issues:

1. origin of life (an emergent event, based on a special set of geochemical conditions (I have my favorite scenarios)). This creates simple life forms, like prokaryotes - no nucleus, limited chemical power and genetics). This has happened at least once on earth, possibly more.
2. Complex single celled life (another emergent event based on two different cells combining to form a single cell like a eukaryotic cell with a nucleus, mitochondria and bunch of other useful stuff). This has happened several times on earth (mitochondria, chloroplasts, and at least two for other inclusions that provide the ability to process other chemical energy sources (I have previously made some posts on these). However, it took ~2 billion years for that to happen (mitochondria and chloroplasts). It required to two different original cell types and the right environment to favor the results of such a combination.
3. Multicellular life made of complex (eukaryote-like) cells. (Emergent event based on having the single cells). Multicellularity has happened many times on earth. There are even multicellular prokaryotes. ITs an easy quick thing.
4. Intelligence, tool use and developing socially accumulated knowledge and space travel or whatever Fermi was talking about. Also an emergent event. Likelihood and the effect of other other factors (like possibly self-nuking) that could affect it arising.

Each of these steps (especially the origin of life) could actually be a fairly tightly clustered series of emergent events that lead to a self-sufficient chemical system capable of reproduction in its specific environment. They might then eventually produce populations of reproducing entities, competing for the same set of resources. Several emergent steps in there.

Another issue is how you define life. This is surprisingly an issue of contention. Personally I like to consider autopoietic chemical systems as a good description of life. Autopoietic systems are systems able to make more of their own parts. This allows them to replace worn-out or used-up parts. If the parts production exceeds the requirements of the replacement needs, extra parts can be made and the system can grow in size. In chemical systems, the parts are chemicals. Biophysically, when membrane bound sphere-like entities get too big, they tend to separate into two or more smaller sphere-like entities. Potentially reproduction. This can lead to reproducing populations competing for the same resources.

The thing to remember is that, if new life formed today on Earth, it would get eaten very quickly. So you can't conclude that life only formed once on Earth.

That sounds like a personal theory to me!

I don't think this is a personal theory. Its just stuff many physicists are not aware of. Its an obvious conclusion from the niche exclusion principle in ecology. (This is also the basis for the competition for resources among different organisms.) If something is using a set of resources, it will presumably become increasingly more efficient at it until physical limits are reached.I think a lot of biology captures something like 95% of the energy it intakes. Life forms just starting out will not be nearly as efficient and will be, quite predictably, out competed. Then any new organism in conflict with established ones for using the same resources, will have to compete for the resources. Unless it could find an alternative niche they can make a living in (as a successful autopoietic system), they will go extinct.
Not only could the new life forms be eaten by earlier evolved guys, but they would also have to out compete them for resources.

In non-scientific and most scientific communications, just discussing life without really defining what you are talking about usually works out fine. However, when talking about things near the boundary between life and not-life, the lack of a commonly accepted definition results in problematic cases. The term is not well suited to refine scientific questions. I would argue that the problems break down based on the emergent events needed to take them to the next stage toward being a complete autopoietic chemical system.

Some traditional examples of problematic cases include:

1. mules: metabolically alive, can not reproduce. Not alive by some definitions.
2. non-reproductive castes of social insects (ants and bees): same issues.
3. fire: a reproducing chemical reaction (dependent on environmental fuel), no inheritance (thus no evolution) other than the initial spark (characteristics completely dependent on the fuel and oxidizer), can reproduce by slitting the fire in two.

With respect to the issue of how many origins of life, this is from a post I made relevant to this in another thread. Important points are summed up in this picture:
LUCE = Last Universal Common Ancestor
LBCA = Last Bacterial Common Ancestor
LACA = Last Archeal Common Ancestor
red lines = horizontal gene transfer between different lineages.
Thick lines LUCA and its derivatives.


Carl Woese thought that before LUCA there could have been many beginnings of life and several of them could have combined to produce a more empowered chemical entity. Producing an anastomosing or reticulate lineage.

Life arising in alkaline hydrothermal vents is probably the dominant scenario for how life on Earth arose. Currently, this mostly happens in locations of ocean floor spreading, but away from magmatic heat sources. They rely on the more gentle heat of serpentinization (weathering of basalt) reactions to drive slow flows of chemically laden water.

When the earth first formed a solid surface with water on top, there were no continents and perhaps some volcanoes emerging from the oceans. All the rest of the surface area of the earth would have been potential sites for serpentinization to occur. This view makes more than one beginning of life not unreasonable.

I suspect we will identify the essential chemical pathways amongst the possible pathways within mixtures of the kinds of chemicals we could expect to occur naturally without biology and under the conditions we expect to have existed - by modeling rather than experiment.

Something like this is a common proposal in abiogenetic hypotheses.
Specifically at alkaline hydrothermal vents uprising chemical dissolved in the flows can react with natural minerals (like FeS crystals) to produce chemicals found int the Krebs cycle. This production can be measured today. The Krebs cycle is a central hub of earthly biochemistry. I is one or two steps from producing several amino acids and some lipids. Several of today's Krebs cycle enzymes have FeS at their active sites.

 

[DaveC426913]

Some traditional examples of problematic cases include:

1. mules: metabolically alive, can not reproduce. Not alive by some definitions.
2. non-reproductive castes of social insects (ants and bees): same issues.
3. fire: a reproducing chemical reaction (dependent on environmental fuel), no inheritance (thus no evolution) other than the initial spark (characteristics completely dependent on the fuel and oxidizer), can reproduce by slitting the fire in two.

I don't grant that mules and ants are germane.
Naively, by that same definition, a barren woman is not alive.

The defintion of life is not about the circumstances of individuals.

And fire can only be labelled alive if you apply the conditions metaphorically.

 

[BillTre]

I don't grant that mules and ants are germane.
Naively, by that same definition, a barren woman is not alive.

Makes sense to me based upon the particular definition you use, which often involve being able to reproduce.

The defintion of life is not about the circumstances of individuals.

Are individuals not alive then?
How would you apply such a definition to particular organisms?

These are among the problems that some of these definitions have to deal with. If they can't not deal with these cases, they are not useful definitions.

 

[256bits]

= 1,300,000,000,000,000,000,000,000,000,000 bacteria's worth.

That's generally the amount of bacterial C in todays water giving a concentration of 2 x 10^-6 Carbon / H20 atoms

 

[DaveC426913]

Makes sense to me based upon the particular definition you use, which often involve being able to reproduce.

Pretty certain no serious scientist thinks that an individual who cannot reproduce is not alive. So it is not the definition anyone uses in the study of life.

Infertile women are not unalive. There is no confusion about that. Therefore, the idea of requiring reproductive ability - as applied to individuals - is mere word play. Pretty sure science has progressed beyond word play.

Are individuals not alive then?

Exactly why individuals have nothing to do with a definition of life. That is known as a category error.

How would you apply such a definition to particular organisms?

Category error.

These are among the problems that some of these definitions have to deal with. If they can't not deal with these cases, they are not useful definitions.

These are not cases; these are category errors.

 

[QuarkyMeson]

It seems to me that if life started on earth exactly once in 4.5 billion years, then it is an extremely improbable event that is a very rare if not unique occurrence in the universe. I’m aware that the number of planets in the universe, including interstellar and intergalactic planets, is an absurdly high number. However, is it possible that abiogenesis is even more unlikely than the amount of places where it could occur? Could the answer to the Fermi paradox be that life is confined to earth?

The universe appears homogeneous and isotropic on large scales. The lower bound for the size of the universe is much much larger than the observable universe. If the universe is truly flat and homogeneous than it's infinite with infinite energy (or finite energy with some weird 3-torus thing and what I'm about to say wouldn't apply then). In that case the question is answerable as a definite it's not very rare, because it's happened an infinite number of times, there's infinite number of observable universes that look just like ours, there's another Earth where someone has posted this same question but on that Earth in English it's spelled Phisics.

If the universe is instead just really really big than it's possible we're alone, but doubtful. We just don't have enough information. We haven't been looking for very long or very hard.

 

[BillTre]

Exactly why individuals have nothing to do with a definition of life. That is known as a category error.

Who are you to say what has to do with definitions of life? There hundreds of them.
One of the most prominent ones is the NASA definition states: life is a self-sustaining chemical system capable of Darwinian evolution. This has been merciously ridiculed since it was made in the 1990's (much as you are doing). It doesn't matter if no one believes it, it is still open to being criticized.

You seem to be both arguing that a definition of life involves the ability to reproduce and does not involve the ability to reproduce.

Infertile women are not unalive.

without specifying how you are making your definition.

You keep saying category error with respect to people's attempts to define life. Sounds like a cop-out.
What is the category you are using to determine something is alive? A metabollically living individual, or a reproducing population, a reproducing population able undergo evolution, all of these together, or something else?

the idea of requiring reproductive ability - as applied to individuals - is mere word play. Pretty sure science has progressed beyond word play.

The possibility to reproduce would probably be acceptable to many people, but mules still remain a big deal for whole classes of definitions. There is a vast literature on this.

You call it word play, but it you want to make solid conclusions based on a definition, then the words have to make sense wrt the subject and its properties.

The whole point I want to make is that there are no really great definitions of life that can be applied in all cases. Especially in the cases where entities lie between some of the details of these definitions. Many definitions are lists of traits that something living would have to have ALL of the traits in the definition to fulfill its and be declared alive.
Instead, using the model of autopoietic chemical systems is more useful in most (maybe all) cases. Preference for a model or theory over a definition is the idea of Carol Cleland, a philosopher that works with NASA on definitions of life.

 

[Filip Larsen]

What is the category you are using to determine something is alive?

I would say that a useful definition has to cater for that organisms often are hierarchical, so while individual member organisms in such a hierarchy may not be able perform all the functions of the combined hierarchy they are a still alive. This means individual ants can be considered alive because they are part of an hierarchical organism we would like to consider a life form. Or in other words, a definition that does not recognize an individual ant as "alive" or part of a "life form" is not very useful in my book.

But true, no matter what (simple) definition you choose which is based on already made observations of "life as we recognize it", some individuals are bound to land on the wrong side of that classification. In discussions about how definitions compare the focus on such "classification errors" are of course interesting and relevant while these "errors" may be less relevant in other discussions.

The OP question is in the context of the Fermi paradox, so I would interpret the question as to what mechanism can give rise to "traces of life" that eventually becomes detectable over interstellar distances. For example, if we one day detect an "alien probe" in our solar system, .e.g. a mechanism somewhat reminiscent of our probes, we would not have any doubt that such a probe must originate with some kind of alien life form even if we have doubts whether or not that particular probe is to be considered alive or artificial in the context of that (yet unknown) alien life form. It seems as our observational methods improve and (hopefully) are able to pick up more signals that could be interpreted as a "trace of life", researchers are likely to repeat and refine what definition of life that will make sense in that context and it may very well depart (e.g. be wider) compared to what would be considered a useful definition of life when applied to phenomenons observed on Earth.

 

[BillTre]

I would say that a useful definition has to cater for that organisms often are hierarchical, so while individual member organisms in such a hierarchy may not be able perform all the functions of the combined hierarchy they are a still alive. This means individual ants can be considered alive because they are part of an hierarchical organism we would like to consider a life form. Or in other words, a definition that does not recognize an individual ant as "alive" or part of a "life form" is not very useful in my book.

For a while, I had a job recovering corneas from dead people. It was an iI also got to interact with the collectors of other body parts of the dead. The cells don't all die when the body does and thus retain some usefulness for a while.
Because of their slow metabolism and reduced needs for nutrients and oxygen corneas, skin, tendons, and blood vessels can be harvested upto 24 hours after death (body usually being cooled to some degree).
Larger more complex organs like kidneys and hearts have to taken out of the body and iced immediately after the heart stops. This is usually done by finding people who are declared brain dead so the orga removal can be coordinated with the stopping of blood flow.
This of course further complicates how you decide what to call dead or alive.
An extreme case would be Henrietta Lacks who died of cervical cancer in 1951. Some cells taken from her before she died continue to live on today as one of the most commonly used cells in cell culturing. This cell line is older than I am.

The OP question is in the context of the Fermi paradox, so I would interpret the question as to what mechanism can give rise to "traces of life" that eventually becomes detectable over interstellar distances. For example, if we one day detect an "alien probe" in our solar system, .e.g. a mechanism somewhat reminiscent of our probes, we would not have any doubt that such a probe must originate with some kind of alien life form even if we have doubts whether or not that particular probe is to be considered alive or artificial in the context of that (yet unknown) alien life form. It seems as our observational methods improve and (hopefully) are able to pick up more signals that could be interpreted as a "trace of life", researchers are likely to repeat and refine what definition of life that will make sense in that context and it may very well depart (e.g. be wider) compared to what would be considered a useful definition of life when applied to phenomenons observed on Earth.

Recently "assembly theory" has been proposed as a way of identifying living things at a distance.
IT is based on counting how many steps of chemical "assembly" are required to make a particular kind of chemical. The same approach could be applied to larger structures that would normally be considered not just chemical. Its a measure of complexity. If things are complex enough they can be safely considered requiring something like a biological process to assemble. The breakpoint is something like 16 steps of assembly.
It is interesting to astrobiology because (in theory) the molecules can be measured with spectroscopy through telescopes (NASA money).
While it does not really define life nor provide a useful model for how life works, it has robust (experimentally verified) claims about picking out possible life chemicals.

These guys (Lee Cronin and Sara Walker) are much better at explaining this than I am:
.