Implications of life being found or not found on Europa

[mfb]

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?

Only if we disassemble Europa and check every cubic micrometer.
We did not find life on Europa so far. Maybe we just did not look close enough (in fact, we did not look at all).
Anyway, I don't think anyone seriously supports that hypothesis.

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?

The point is to avoid introducing actual priors as long as possible.
Not finding life would rule out overly optimistic hopes that life evolves basically everywhere. It wouldn't do much else.
Finding life would rule out many low estimates for the probability that life evolves (assuming an independent origin) or exists (if they share ancestors with life on Earth).

We cannot prove interstellar distribution of life within the solar system - no matter what we find, "evolved independently in the solar system" and "distributed within the solar system" together can explain all reasonable observations. Sure, fossils of highly complex multicellular organisms billions of years old would support life from elsewhere, but we didn't find anything like this on Earth.

 

[1oldman2]

How about this? it is probably water soluble.

http://www.bbc.com/news/science-environment-35991312

 

[Jeff Rosenbury]

I'm curious how life could not exist on Europa.

The Earth has been shedding life for billions of years. Tectonic activity blasts life bearing rocks into space. While most of this could be expected to die out, it is possible at least some of the complex amino acids would find their way to other planets.

I suspect anywhere capable of sustaining life has life, at least on the single cell level. A billion years is a long time.

To me the interesting question is, how close to Earth life is E.T. life? Are we related, or is it distinctly evolved? (For that matter, did we first evolve on earth, or are we descended from seeded alien bacteria ourselves?)

 

[anarchean]

Anyway, I don't think anyone seriously supports that hypothesis.

I was already going to ask if that's is a thing. I don't know much of biology, but I didn't thnk chemo-genesis has ever used that as part of the hypotheses.
The converse on the other hand seems to hold. For now.

 

[EinsteinKreuz]

I daresay that TITAN, and not Europa, is the best place in our solar system(beyond Earth) to look for extant life. Something is consuming its atmospheric hydrogen...

 

[KenJackson]

Not a single post, as far as I can see, has mentioned the underlying premise that assumes life can spontaneously arise from nonliving material. Yet there's never been an observed instance of it. Sure, you can say that we're here so it must have happened, but that's an assumption, and it's foundational to this discussion.

The Earth has been shedding life for billions of years. Tectonic activity blasts life bearing rocks into space. While most of this could be expected to die out, it is possible at least some of the complex amino acids would find their way to other planets.

Good point. It's possible that life could have been transported from Earth to some other body in this solar system, so maybe we'll find earth-like life there.

 

[Buzz Bloom]

Something is consuming its atmospheric hydrogen...

Hi EK:

Can you please cite a reference for the above? Isn't it possible that the hydrogen in Titan's atmosphere is just gradually escaping?

Regards,
Buzz

 

[mfb]

Titan's gravitational field is not strong enough to hold molecular hydrogen over geological timescales.

Sure, you can say that we're here so it must have happened, but that's an assumption, and it's foundational to this discussion.

There is no other possibility, unless we have some sort of eternal universe structure where life existed forever. And I am not aware of any plausible theory for that.
It didn't have to happen on Earth, but somewhere it did have to happen.

 

[KenJackson]

There is no other possibility, ...

A lot of people have said that about a lot of things and were wrong.
I'm just saying it's a critical assumption that should be stated up front.

 

[mfb]

It is elementary logic. It can be as much wrong as A=A. If it exists today, then either it formed at some point (at least once), or it existed forever.

 

[OrangeDog]

I feel like we need to understand how life forms before we can assert the significance of finding or not finding life on Europa. I have thought that it would be a wise idea to try to start life on mars. We have a good enough understanding of the planet and extremophiles on Earth to send them to the surface of Mars, give them time to grow (or die), and record our observations.

 

[rootone]

Not a single post, as far as I can see, has mentioned the underlying premise that assumes life can spontaneously arise from nonliving material. Yet there's never been an observed instance of it. Sure, you can say that we're here so it must have happened, but that's an assumption, and it's foundational to this discussion.

Well the early state of the universe as soon as matter became possible seems to have been a lot of hydrogen, some helium as well, and a bit of lithium,,
That's not exactly living material is it?

 

[rootone]

I feel like we need to understand how life forms before we can assert the significance of finding or not finding life on Europa. I have thought that it would be a wise idea to try to start life on mars. We have a good enough understanding of the planet and extremophiles on Earth to send them to the surface of Mars, give them time to grow (or die), and record our observations.

Extremophiles on Earth have adapted to the most extreme conditions on Earth.
That does not imply that they should therefore adapt to conditions on Mars.
Although if there are extromophiles on Earth which can propagate in frozen tundra with no oxygen, well maybe, .. are there any?

 

[EinsteinKreuz]

Hi EK:

Can you please cite a reference for the above? Isn't it possible that the hydrogen in Titan's atmosphere is just gradually escaping?

Regards,
Buzz

Citation as requested.I'm not claiming there is life on Titan, but despite the fact that it's gravity cannot hold onto molecular clouds, the fact that 95% of Titans orbit is within Saturns magnetosphere helps shield Titan from buffeting solar winds that would otherwise erode its atmosphere even though AFAIK Titan does not appear to have an internal magnetic field.

 

[Rubidium_71]

From what I've read, it seems like life in Europa's ocean would be more likely to exist if hydrothermal vents are present. We've seen life cluster around hydrothermal vents here on Earth, benefiting from the minerals and heat that are expelled. As has been mentioned, the presence of water is one data point. It seems like the presence of vents would be point #2.
Io has enough energy from tidal flexing to produce volcanoes. Has anyone ever calculated if Europa, being further away from Jupiter, still has enough tidal flex energy to produce any hydrothermal vents? Not sure if we have enough information to do the math on that yet. I assume another probe would probably be needed for a thorough analysis.
I think we can all agree there's liquid water present, but are we talking about a dead, sterile, luke warm fluid layer or an ocean actively fed by hydrothermal vents?

 

[Buzz Bloom]

I feel like we need to understand how life forms before we can assert the significance of finding or not finding life on Europa.

Hi OD:

Even if science does not yet have a understanding of how life formed, the finding or the not finding of life on Europa would be significant for the following reasons.

Finding life on Europa would be significant for many reasons. For one example: the reason life is speculated to be a possibility on Europa is based on Europa's water, so life found there would likely be water based. Science would then learn something new about the nature of water based life, and how Europa's life is similar to or dissimilar from Earth life. This would enable science to gain a clearer insight into what are the essential environmental requirements for water based life.

Not finding life in Europa would presumably lead to an analysis of what are the differences between Europa's and Earth's environments that are most likely to be relevant to explaining the absence of life on Europa.

Regards,
Buzz

 

[Jeff Rosenbury]

Good point. It's possible that life could have been transported from Earth to some other body in this solar system, so maybe we'll find earth-like life there.

Not just our solar system. A billion years is a long time. Whether life could survive a slow interstellar journey depends on conditions in interstellar space. I wish we knew more about these, but it's a long way to the edge of the solar wind. Perhaps NASA will give it a try someday.

Many stars seem to live just a few million years. These are the hot, heavy ones that likely make heavier elements.

So this does just kick the can down the road a bit. Life obviously evolved somewhere. But conditions elsewhere may have been significantly different than conditions here. So there are possibilities that many people don't consider, like formation in strong EM fields, etc.

 

[newjerseyrunner]

Not just our solar system. A billion years is a long time. Whether life could survive a slow interstellar journey depends on conditions in interstellar space. I wish we knew more about these, but it's a long way to the edge of the solar wind. Perhaps NASA will give it a try someday.

Yeah, a billion years is a long time, that also equates to a lot of increase in entropy. It's highly highly unlikely that even the toughest organisms could survive an average interstellar journey. It could however (probably) survive transport between stars in a stellar nursery where journeys between stars aren't as long.

 

[mfb]

Cells as old as 250 million years can be revived. 20 km/s are ~7 light years per million year, sufficient to travel from one planetary system to a different one. Sure, interstellar space gives much more radiation damage than rock on Earth, but we have a safety factor of at least 250 in terms of time.

 

[KenJackson]

Life obviously evolved somewhere.

Life exists, therefore it must have evolved?

That's an assumption without evidence or even a plausible mechanism. Assumptions and hypotheses are a necessary part of science, but good scientists state and constantly question their assumptions.

This reminds me of physics discussions that were ongoing a hundred years ago. The electron was in one orbital and now it's in the next, therefore it MUST have existed in between at some some point at least briefly. It's OBVIOUS. It COULD NOT have just jumped from one orbital to another.

The topic then was probably just as emotional as this one. Hopefully science will win out like it did then.

 

[rootone]

I think jeff means, life obviously does exist in at least one instance, so therefore the necessary chemistry and conditions are 'de facto' possible.
'evolve' might have been unwise way of saying that.

 

[Jeff Rosenbury]

Life exists, therefore it must have evolved?

That's an assumption without evidence or even a plausible mechanism. Assumptions and hypotheses are a necessary part of science, but good scientists state and constantly question their assumptions.

This reminds me of physics discussions that were ongoing a hundred years ago. The electron was in one orbital and now it's in the next, therefore it MUST have existed in between at some some point at least briefly. It's OBVIOUS. It COULD NOT have just jumped from one orbital to another.

The topic then was probably just as emotional as this one. Hopefully science will win out like it did then.

If we accept evolution as change over time, then we have observed evolution. There is plenty of evidence.

If we go with strict Darwinism, then it has already been disproven. (Strict Darwinism disallows cross species genetic transfer, which we know happens.)

The truth seems to lie between these two extremes.

It is certainly possible that some randomly occurring, self organizing, emergent intelligence meddled to start life, or even that life is such a thing. But life has clearly changed in the modern, historical period. Discounting that (Ex. -- The universe was created 5 seconds ago, and history is just some random bits and pieces.) undermines not just the meaning of science, but the meaning of language.

 

[mfb]

Life exists, therefore it must have evolved?

It does not matter which word you use for it. It also does not matter if our own origin was from anorganic chemistry, or if earlier life messed around and created our ancestors deliberately - because that just shifts the time where life first formed from non-life. As long as we have some time-ordering in the universe, there was either a first point in time with life, or life existed forever. That is a mathematical fact.

 

[Buzz Bloom]

Hi @ogg:

Your post #31 raise quite a few interesting points, some of which I find a bit confusing.

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.

I certainly agree that science currently provides almost no details about the sequence of events leading up to the first living cell. The following are a few events that seem to have a “known” sequence. By “known” I mean that among those scientists who work in this field, most agree about the sequence below is most likely to be correct.
1. Abiotic manufacture of organic molecules, e.g., amino acids, sugars, nucleotides. This is generally called the “organic soup” phase.
2. The “RNA world” in which relatively long RNA double helix chains are able to reproduce themselves repeatedly with relatively good accuracy which improves over time.
3. Ribosome-like combinations of RNA (without proteins) that enable manufacture of amino acid sequences based on the neucleodtide sequences a single RNA strands. This is the emergence of proteins.
4. The emergence of DNA.
5. The first cell.

I do not understand what you mean by

We should admit our ignorance, and move on, but not pretend it doesn't exist.

I assume that “admit our ignorance” means acknowledge that science currently knows very little about the details of the sequence of events leading to the first cell. Also, I am guessing that “not pretend it doesn't exist” means you interpret the current discussion and research about the origin of life as ignoring this limitation of current knowledge.
Can you clarify what “and move on” means?

We also need to be careful about what we mean by "life".

I agree. Speculation about life on Europa is because Europa has water. My original intent was to encourage speculation about conditions that are necessary for water based life to evolve from non-life.

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.

The seems to me be a misunderstanding of the thread's discussion. I would expect that most of the PF participants agree that science never “knows” anything with absolute certainty. Science makes an effort to constantly improve understanding, and this process requires that in principle anything currently “known” can later be found to be incorrect. As more and more tests are made to validate what is “known”, and these tests continue to fail to invalidate what is “known”, then the confidence regarding the tested knowledge improves, but it never becomes certainty.

at some point we will seed those planets and moons which can support it.

I confess I was surprised when this thread began to speculate about the transfer of life from one planet/moon to another. My original intent was to seek speculation about implications regarding suitable environments where life might evolve from non-life.

Regards,
Buzz

 

[anarchean]

@Buzz Bloom Man, I think I got your point of view.
You are saying that if we don't find life of Europa, that will make possible for us to compare our environment with Europa's and possibly lapidate our current hypothesis for chemo-genesis. Right?

If that's right, I agree with you. It'll certainly apply some filters to genesis of life. May remove some filters too, I don't know.
But I still don't think it'll have such a huge impact as finding life there, which will certainly remove some filter for life.

Side question: Does Europa have material for creating organic stuff? I mean, there is carbon material there enough to create carbon-chain molecules?

 

[jim mcnamara]

Comets have bombarded most any larger sized object in the Solar System. So whatever organic chemicals you can find on a comet has a very good chance of existing on a large moon.

Latest report - ribose (sugar that is part of RNA) "found" on comets: the space.com version
http://www.space.com/32503-artificial-comet-creates-life-building-blocks.html

 

[newjerseyrunner]

Cells as old as 250 million years can be revived. 20 km/s are ~7 light years per million year, sufficient to travel from one planetary system to a different one. Sure, interstellar space gives much more radiation damage than rock on Earth, but we have a safety factor of at least 250 in terms of time.

Yeah, but surely you agree that stowing away on an asteroid through interstellar space is a different kind of beast than sitting cozy under the ground of Earth for 250 million years. In space, every pice of space debris hits your asteroid with the power of a bullet and dowsed in radiation.

 

[anarchean]

http://www.space.com/32503-artificial-comet-creates-life-building-blocks.html

That's amazing! The organic material on Earth could come from asteroids too. Pretty cool.

That leaves one question open, how did this organic materials are formed in the steroids?
Do you know any hypothesis?

 

[rootone]

how did this organic materials are formed in the steroids?

Carbon is quite a common element found throughout the Universe.
So also are two other elements necessary for life as we know it, Oxygen and Nitrogen.
All of these are cooked up in considerable amounts by fusion inside medium to large stars.
The carbon in comets and asteroids would have been already present in the original solar nebula before any solid bodies formed.

 

[mfb]

Yeah, but surely you agree that stowing away on an asteroid through interstellar space is a different kind of beast than sitting cozy under the ground of Earth for 250 million years. In space, every pice of space debris hits your asteroid with the power of a bullet and dowsed in radiation.

Radiation is the only difference for those crystals that do not break up. The radiation dose depends on the size of the object and the position of the bacterium inside. 10 meters of rock give similar shielding as the atmosphere of Earth.

 

[litup]

The first thing I would want to know, assuming we found life on Europa, is this life form based on something like our style of DNA and RNA. If so, that life probably originated independently and it would say for instance, maybe our kind of life came from a cloud that seeded the whole solar system with prebiotic molecules that had a statistical chance of forming our kind of life, based on DNA and so forth.

If the life form was based on a structure like a 4 sided DNA kind of thing, it might be telling us there are many other ways of making life in the universe than just what we already know.

 

[Buzz Bloom]

Hi anarchean:

You are saying that if we don't find life of Europa, that will make possible for us to compare our environment with Europa's and possibly lapidate our current hypothesis for chemo-genesis. Right?

Yes. BTW, I learned a new word today: lapidate: 1. to pelt with stones 2. to kill by stoning. Nice metaphor.

Does Europa have material for creating organic stuff? I mean, there is carbon material there enough to create carbon-chain molecules

http://www.nasa.gov/topics/solarsystem/features/europa20130404.html

Regards,
Buzz

 

[newjerseyrunner]

Radiation is the only difference for those crystals that do not break up. The radiation dose depends on the size of the object and the position of the bacterium inside. 10 meters of rock give similar shielding as the atmosphere of Earth.

What about 250 million years of micro-meteroid impacts? Violent shockwaves are just as lethal and much more common on asteroids than deep under the Earth's surface.

 

[Feeble Wonk]

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

I'd agree with you in some respects Buzz. If multicellular life was found I'd think that would provide strongly compelling evidence (convincing evidence IMHO) that life in "some" form will be extremely common on most life-compatible planets in the "Goldilocks Zone" of countless stellar systems of sufficient age scattered throughout the cosmos. But even only unicellular life on Europa would be significant evidence of that.

On the other hand, as already suggested, if the life form(s) found on Europa had a demonstrably common genetic ancestry with Terran life, it would essentially confirm panspermia AT LEAST WITHIN OUR SOLAR SYSTEM. Yet, that might actually be less compelling evidence that life is common throughout the cosmos as a whole, when compared to the implications of finding life on Europa of independent genetic origin. Though, I would agree with the other opinions that failure to find life on Europa would not significantly diminish expectations of life being present on more hospital planets in other solar systems.

 

[Buzz Bloom]

failure to find life on Europa would not significantly diminish expectations of life being present on more hospital planets in other solar systems.

Hi FW:

The estimate of "expectations" would seem to be related to the f_l term in Drakes equation:

f_l = the fraction of planets that could support life that actually develop life at some point​

Why is it unreasonable to calculate an estimate as follows.

Based on what is now known, mostly from knowledge of life on one single world with life (Earth), an estimate is made:

f_l = E.​

The uncertainty of this value would of course be very large.

If we assume that Europa satisfies the criteria for being planets that could (possibly) support life, and we assume that no life is found on Europa, then we now how two data points: one with life and one without life. Assume that science finds no differences between Europa's and Earth's that science believes to be significant enough to change our classification of Europa as a being a kind of planet than can support life. I suggest that it would then be reasonable to modify our estimate form

f_l = E​

to

f_l = E/2 .​

Assume we ignore the possibility of life migration from one planet to another. If this calculation is reasonable, then the result would be that our expectation of life being present on hospital planets in other solar systems is cut in half.

Regards,
Buzz