Implications of life being found or not found on Europa

[Buzz Bloom]

Wikipedia

https://en.wikipedia.org/wiki/Europa_(moon)#Subsurface_ocean​

says that

"Scientists' consensus is that a layer of liquid water exists beneath Europa's surface, and that heat from tidal flexing allows the subsurface ocean to remain liquid."​

There have been speculations that Europa might contain life. For example,

"Europa is the most likely place in our solar system beyond Earth to possesses ... life," said Robert Pappalardo, a planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
http://phys.org/news/2013-02-jupiter-europa-moon-likeliest-life.html
​

I am curious to find out what the knowledgeable participants at PF speculate the implications are if, someday, life is found on Europa, or Europa is found to not have life. In particular how will such a finding affect the likelihood that life exists on some exoplanet in the Milky Way. That is, to what extent would finding (not finding) life on Europa affect the probability that life exists (does not exist) elsewhere in the Milky Way.

Another area of interesting speculation would be: If life is not found on Europa, what particular difference(s) between Earth and Europa might explain this. For one example, it might be that liquid water temperatures on Earth range from < 0 C (due to salts in the ocean) to 100 C (due to sub-ocean mantle plumes), while the range of water temperatures on Europa are likely to be more limited.

 

[phinds]

Not finding life on Europa would be just boring and of no particular consequence, but FINDING it, or finding life anywhere other than Earth, would be a big deal indeed.

 

[Ygggdrasil]

An interesting question if life exists on Europa would whether it seems to share a common ancestor with life on Earth. Common ancestry could provide support for theories of panspermia, whereas an independent origin of life would suggest that abiogenesis is fairly common and we should expect to find life in similar environments across the universe..

 

[Greg Bernhardt]

Common ancestry

Would it matter if it were single cell or multi-cell?

 

[Ygggdrasil]

Would it matter if it were single cell or multi-cell?

Nope. I would suspect the common ancestor, if one were to exist for these hypothetical lifeforms, would have been a single-celled organism (probably similar to the LUCA on Earth).

 

[Buzz Bloom]

Not finding life on Europa would be just boring and of no particular consequence

Hi phinds:

I confess I am surprised by this answer. I would think that it would constitute, among other things, very strong evidence that just having water on a planet/moon is not sufficient for life to evolve there.

Regards,
Buzz

 

[Buzz Bloom]

Would it matter if it were single cell or multi-cell?

Hi Greg:

Yes, I think this would matter with respect to the likelihood that multi-cell life exists on exoplanets in the Milky Way. It would also matter a lot if the Europa multi-cell life were not like Earth's Eukayotes, but consisted of instead of bacteria-like or Archaean-like cells.

Regards,
Buzz

 

[phinds]

Hi phinds:

I confess I am surprised by this answer. I would think that it would constitute, among other things, very strong evidence that just having water on a planet/moon is not sufficient for life to evolve there.

Regards,
Buzz

Absence of evidence in a particular case is not evidence of absence in general.

 

[Pepper Mint]

I would just want to make the thread more colorful...

...if, someday, life is found on Europa, or Europa is found to not have life.

Is that still a young planet ? I agree with phinds about this that it doesn't really matter if life isn't found on Europa since our discovery of new lifeforms outside the earth, no matter where it will be, I think would be more important.

In particular how will such a finding affect the likelihood that life exists on some exoplanet in the Milky Way. That is, to what extent would finding (not finding) life on Europa affect the probability that life exists (does not exist) elsewhere in the Milky Way.

Very likely, because it helps us confirm our theories on what basic materials these lifeforms need to evolve from right on Europa and further make other assumptions about life possible in other planets if the same conditions are met.

It would also matter a lot if the Europa multi-cell life were not like Earth's Eukayotes, but consisted of instead of bacteria-like or Archaean-like cells.

How would it matter then ? I think it is how the first cells are born, though.
And it is true that some lifeforms can survive and evolve without water as their prerequisite.

Absence of evidence in a particular case is not evidence of absence in general.

very true.

 

[Buzz Bloom]

Hi Pepper Mint:

You asked

"How would it matter then?"​

regarding what I said

"It would also matter a lot if the Europa multi-cell life were not like Earth's Eukayotes, but consisted of instead of bacteria-like or Archaean-like cells."​

I have recently been reading (and enjoying) The Vital Question by NIck Lane (2015), in which a well reasoned argument is given about why bacteria and Archaea failed to evolve into multi-cellular creatures.

You ares said:

And it is true that some lifeforms can survive and evolve without water as their prerequisite.

What is your basis for claiming this is true?

Regards,
Buzz

 

[Ygggdrasil]

I have recently been reading (and enjoying) The Vital Question by NIck Lane (2015), in which a well reasoned argument is given about why bacteria and Archaea failed to evolve into multi-cellular creatures.

It is worth noting that not all agree with Lane and other who make such arguments. Here is a nice paper arguing that, as eukaryotes ourselves, we tend to hold a eukaryo-centric view of evolution: http://www.pnas.org/content/112/33/10278.abstract

That said, as eukaryotes comprise all complex life and there are no known examples of complex prokaryotic life, there may be something to the arguments of Lane and others.

 

[newjerseyrunner]

Both would have huge implications.

Not finding it means that there is some filter for life that we haven't figured out yet, it'll also provide information about the Drake equation by showing us that even simple life is rare. Europa's oceans seem perfect, if there isn't life there, we're not understanding something.

If there is life there, I'd be very interested to take it's genome and find out if we're related. It'd be strong evidence that Earth life may not have started on Earth. We might be able to calculate backwards and figure out how long ago our common ancestor likely lived. If that number is older than the solar system, well then that means that life is probably extremely common since it can spread between stars easier than we think it can now. Right now it's assumed that nothing could survive an interstellar journey, not even the toughest microbes. If that number is about the same age as the solar system, that means life can migrate between planets, but provide little to no information about beyond that.

 

[rootone]

... Europa's oceans seem perfect ...

Other than that a subsurface ocean seems likely to exist beneath a thick ice crust, I don't think we know much more about it at this stage.

 

[phinds]

Not finding it means that there is some filter for life that we haven't figured out yet ...

What do you base that on? Just because there are good conditions for life doesn't mean that has to BE life.

 

[ProfuselyQuarky]

Just because there are good conditions for life doesn't mean that has to BE life.

I have so many things to say about this . . . :(

 

[jim mcnamara]

@phinds is saying 'you cannot logically disprove a hypothesis with a single experiment/exploration because you would need to enumerate all cases'. < good!
You establish a better explanation/hypothesis and test that instead. Since everyone is making assumptions here is one: we may make tests for life that the 'lifeforms' in Europa's oceans fail. This is an example of why failure is not the endpoint. This somewhat absurd example is also why our 'Eukaro-centric' worldview could get us a false negative as well.

 

[newjerseyrunner]

What do you base that on? Just because there are good conditions for life doesn't mean that has to BE life.

No, but we tend to make that assumption based on the single data point that life on Earth started essentially as early as it could. It's (circumstantial) evidence that if the conditions are right, life will just go. If the oceans down there seem perfect, but there is nothing there, we'll have to rethink how easy it is, and therefore wonder why it happened so quickly on Earth. It'd also bring new life to the Rare Earth idea, which has fallen out of favor in the recent flood of exoplanets.

 

[phinds]

No, but we tend to make that assumption based on the single data point that life on Earth started essentially as early as it could. It's (circumstantial) evidence that if the conditions are right, life will just go. If the oceans down there seem perfect, but there is nothing there, we'll have to rethink how easy it is, and therefore wonder why it happened so quickly on Earth. It'd also bring new life to the Rare Earth idea, which has fallen out of favor in the recent flood of exoplanets.

I understand what you're saying but I think you're giving too much weight to a single data point.

 

[Alltimegreat1]

"Europa is the most likely place in our solar system beyond Earth to possesses ... life,".

With regard to the likelihood of finding life in the Solar System, if Earth is #1 and Europa is #2, what planets/moons would be #3, #4, and #5?

 

[newjerseyrunner]

With regard to the likelihood of finding life in the Solar System, if Earth is #1 and Europa is #2, what planets/moons would be #3, #4, and #5?

Ganymede, Enceladus, and Mars are all candidates for life as we know it and Titan has the potential for more exotic life.

 

[Buzz Bloom]

With regard to the likelihood of finding life in the Solar System, if Earth is #1 and Europa is #2, what planets/moons would be #3, #4, and #5?

Ganymede, Enceladus, Titan, Mars.

Hi Alltimegreat1 and newjerseyrunner:

https://en.wikipedia.org/wiki/Enceladus says that the Saturn moon Enceladus, like Europa, also has a significant amount of liquid water. I think that would qualify it as #3.

https://en.wikipedia.org/wiki/Ganymede_(moon) gives a description of Ganymede as not having liquid water, so I would leave that one out of the list.
Similarly, https://en.wikipedia.org/wiki/Titan_(moon) says no liquid water on Titan.

https://en.wikipedia.org/wiki/Mars says

"Mars once had large-scale water coverage on its surface at some earlier stage of its existence".​

That would make it a possible candidate for perhaps having had life at some time in the past, but not now. Maybe that would qualify as #4.

I can not think of a #5 candidate.

Regards,
Buzz

 

[Ygggdrasil]

https://en.wikipedia.org/wiki/Ganymede_(moon) gives a description of Ganymede as not having liquid water, so I would leave that one out of the list.
Similarly, https://en.wikipedia.org/wiki/Titan_(moon) says no liquid water on Titan.

Researchers have speculated about the possibility of life existing in non-aqueous environments, for example see: https://www.physicsforums.com/threads/what-might-cell-membranes-look-like-on-titan.800524/

 

[Buzz Bloom]

I understand what you're saying but I think you're giving too much weight to a single data point.

Hi phinds:

I am wondering what some sort of Bayesian analysis might show regarding the effect of such "a single data point" (i.e., finding no life on the watery Europa) on estimating the probability of exoplanet life in the Milky Way, or on estimating the probability of life on a watery exoplanet in the Milky Way. What priors would you use?

Do you agree that finding no life on Europa would logically PROVE that a hypothesis that liquid water is SUFFICIENT for live to evolve is FALSE?

If you do agree, then what hypotheses would you speculate to be plausible for additional conditions that are present on Earth to be sufficient along with liquid water for exoplanet life?

Regards,
Buzz

 

[Ygggdrasil]

Do you agree that finding no life on Europa would logically PROVE that a hypothesis that liquid water is SUFFICIENT for live to evolve is FALSE?

What if life existed in the past and has gone extinct?

 

[Buzz Bloom]

Researchers have speculated about the possibility of life existing in non-aqueous environments

Hi Ygggdrasil:

I also find it interesting to read about the speculations of scientists regarding life without water.

It might well be useful to reconsider the Drake equation as specifically seeking the probability of water based life, rather than any kind of life. Since the nature of possible non-water based life is at the present time so unclear, it seems that trying to make any plausible estimates for

n_e = the average number of planets that can potentially support life per star that has planets​

with respect to non-water based life is currently impossible.

Regards,
Buzz

 

[Buzz Bloom]

What if life existed in the past and has gone extinct?

Hi Ygggdrasil:

You raise a good point. I should rephrase my question as follows:

Do you agree that finding no life, or no evidence of any extinct life, on Europa would logically PROVE that a hypothesis that liquid water is SUFFICIENT for life to evolve is FALSE?

ADDED

With the above refinement to the question, it might possibly also be asked with respect to Mars if at some point evidence of a substantial amount of surface water for an extended period of time is found there. With that in mind I offer the following rewrite:

If at some point evidence of a substantial amount of surface water for an extended period of time is found on Mars, do you agree that finding no life, or no evidence of any extinct life, on Mars would logically PROVE that a hypothesis that abundant liquid water for a long extended period of time is SUFFICIENT for life to evolve is FALSE?

Regards,
Buzz

 

[newjerseyrunner]

Hi Alltimegreat1 and newjerseyrunner:

https://en.wikipedia.org/wiki/Enceladus says that the Saturn moon Enceladus, like Europa, also has a significant amount of liquid water. I think that would qualify it as #3.

https://en.wikipedia.org/wiki/Ganymede_(moon) gives a description of Ganymede as not having liquid water, so I would leave that one out of the list.
Similarly, https://en.wikipedia.org/wiki/Titan_(moon) says no liquid water on Titan.

https://en.wikipedia.org/wiki/Mars says

"Mars once had large-scale water coverage on its surface at some earlier stage of its existence".​

That would make it a possible candidate for perhaps having had life at some time in the past, but not now. Maybe that would qualify as #4.

I can not think of a #5 candidate.

Regards,
Buzz

Ganymede is thought to have large salt water oceans, look closer at the wiki page you mentioned. There are many separate indications of this ocean.

Titan has liquid hydrocardons which is capable of supporting complex chemistry. Life there would likely break hydrogen and be fueled be acetylene.

Mars has no surface water, it's got vast quantities of water deep underground where it's still warm.

 

[Pepper Mint]

https://en.wikipedia.org/wiki/Enceladus says that the Saturn moon Enceladus, like Europa, also has a significant amount of liquid water. I think that would qualify it as #3.

https://en.wikipedia.org/wiki/Ganymede_(moon) gives a description of Ganymede as not having liquid water, so I would leave that one out of the list.
Similarly, https://en.wikipedia.org/wiki/Titan_(moon) says no liquid water on Titan.

https://en.wikipedia.org/wiki/Mars says

"Mars once had large-scale water coverage on its surface at some earlier stage of its existence".​

That would make it a possible candidate for perhaps having had life at some time in the past, but not now. Maybe that would qualify as #4.

I can not think of a #5 candidate.

6 candidates are here.

...
What is your basis for claiming this is true?...

These micro-organisms were found to live their lives via chemo-synthesis and water was only used as an indirect means to produce their foods.

 

[Ygggdrasil]

These micro-organisms were found to live their lives via chemo-synthesis and water was only used as an indirect means to produce their foods.

These organisms are still primarily composed of water (i.e. it is the primary solvent composing the cytosol of the cells).

 

[Buzz Bloom]

These micro-organisms were found to live their lives via chemo-synthesis

Hi Pepper Mint:

Thank you for your references. I much like the six candidate reference for teaching me something I did not previously know. I find the Venus speculation quite amazing in its ingenuity.

The http://www.livescience.com/27899-ocean-subsurface-ecosystem-found.html
article says:

"DNA evidence indicates the organisms are modern and not 3.5-million-year-old fossils, Lever said."​

As I read this article it seems clear that the authors do not believe these organisms evolved from non-life in a non-water environment.

Although bacteria and Archaea have never developed the complexity to become multi-cellular, these organisms certainly have evolved to fill many unexpected niches. However, the logic seems to be that such organisms as described in the article would not be expected to be found on an exoplanet that did not currently, or at sometime in its past for an extended period of time, have a lot of water.

Regards,
Buzz

 

[ogg]

It's going without saying that we don't know which sequences of which events in which environments are able to create "life". We should admit our ignorance, and move on, but not pretend it doesn't exist. We also need to be careful about what we mean by "life". We know (for sure) that certain chemicals, temperatures, and radiation fields make life impossible. We can't make an exhaustive list of these "poisons" because of the ill-defined nature of life and the open ended nature of chemistry. Additionally, this thread seems to be assuming that we will somehow someday know for certain that nowhere on a given planet or moon could support life or it's genesis. Can you prove that nowhere in your backyard is a diamond? I personally think that (if our civilization contiues for another 100 or 200 years, which is far from certain) at some point we will seed those planets and moons which can support it. Finally, keep in mind that liquid water can exist up to ~370°C (I don't know if we know what the lowest possible Temp is for a solution "sufficiently polar" to support life) but that it's almost certainly true that life as we know it cannot exist at that temperature. So, there are chemical, radiation, temperature, (and perhaps magnetic or pressure) contraints on where life can be supported; its probably true that abiogenesis is even more sensitive to these poisonous situations. But a moon is a vast, vast thing. When do you suppose we will have identified all species of life (and all niches) on our own Planet? No time soon, I think...

 

[phinds]

Do you agree that finding no life on Europa would logically PROVE that a hypothesis that liquid water is SUFFICIENT for live to evolve is FALSE?

I ALREADY think that such a hypothesis is clearly false. No amount of distilled water is going to give rise to life.

 

[Buzz Bloom]

No amount of distilled water is going go give rise to life.

Hi phinds:

I get that you think my question was a bit silly, but I have been having some difficulty in understanding what your point of view actually is regarding this thread.

I do appreciate your answering the silly question, but I am disappointed that you ignored the followup question:

If you do agree, then what hypotheses would you speculate to be plausible for additional conditions that are present on Earth to be sufficient along with liquid water for exoplanet life?

Regards,
Buzz

 

[phinds]

Hi phinds:

I get that you think my question was a bit silly, but I have been having some difficulty in understanding what your point of view actually is regarding this thread.

I do appreciate your answering the silly question, but I am disappointed that you ignored the followup question:Regards,
Buzz

Buzz, I have no idea what needs to be present along with water, just that SOMETHING does; that was my point. This is not my field at all so pointless for me to speculate.

 

[rootone]

It's not surprising that water looks to be essential for life, simply because water is very effective at being a medium (solvent) in which many kinds of chemistry are possible.
Carbon chemistry in particular.