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Here are a couple press conferences that summarize what Perseverance has found so far.

Recently Perseverance has been finding organic molecules in every sample it takes. We won't be able to tell if those molecules are of biological original until we get rock samples back to Earth in 2033 or so.

If those samples turn out to be abiotic, will we conclude

  • Life most probably did not arise on Mars
  • or perhaps life arose, but we haven't found it yet?

Clarification

@Fred's answer is good (+$1$), but not quite what I had in mind. Perhaps this is a better way to state it.

  • If life existed on Mars, what are the odds that Perseverance will find evidence of it?
  • If Perseverance does not find evidence of life, what are the odds that life never existed on Mars?

Or if life existed on Mars,

  • What are the odds that it was present in Jezero crater?
  • If present, what are the odds that evidence was preserved?
  • If preserved, what are the odds of Perseverance finding it?

I understand that Jezero crater had water and the pH was around neutral. This makes it likely that life was there if life was anywhere. But I don't know how likely.

Likewise, I understand this is a good place to preserve organic chemicals. After all, we are finding them everywhere. But that doesn't mean they are 3.5 billion years old.

Perseverance is clearly finding the kind of chemicals that could signify life. But I don't know how common those chemicals would be expected to be. Rare like fossils on Earth? Everywhere like organisms today on Earth?

How quantitative can we be about this?

Addition

Here are a couple more relevant items:

A post from 4 years ago about Curiosity's findings - What exactly are the recent observations of organics on Mars? What's the data?

A Dr. Becky Smethhurst video from a year ago - An unsolved Martian methane mystery! Is methane on Mars produced by life?

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  • $\begingroup$ Many people are interested in expressing uncertainties in terms of chance and odds, I appreciate that. But here it seems we have not only no population from which samples can be drawn, but also no realistic way of constructing a hypothetical population. So it's unclear what significance any statements of chance or odds can have? $\endgroup$
    – terry-s
    Commented Dec 6, 2022 at 20:29
  • $\begingroup$ @terry-s - Derived from theoretical models? It seems that NASA would have done all they can to figure out the chances of success before sending a mission. $\endgroup$
    – mmesser314
    Commented Dec 6, 2022 at 20:34
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    $\begingroup$ I think it is so premature to do a sample return mission to Jezero crater. Many scientists will agree that for a good chance to find past life you have to bore at least tens of cm. deep to get samples undamaged by radiation. I think the ExoMars rover will have a much better chance in finding undamaged organics from (past) life. $\endgroup$
    – Cornelis
    Commented Dec 7, 2022 at 17:03
  • $\begingroup$ If Perseverance finds unequivocal evidence that life did exist on Mars, the answer is an unequivocal, emphatic, all-caps YES. On the other hand, if Perseverance finds lackluster evidence or even no evidence at all that life did exist on Mars, the answer is not necessarily no. NASA might have been looking in the wrong places or looking for the wrong signs. Lack of evidence is not necessarily evidence of lack. $\endgroup$
    – David Hammen
    Commented Dec 12, 2022 at 14:00

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No, it's not likely because Perseverance can only drill down to around 5 cm. and at those depths amino acids and other organic biosignatures would have been destroyed by radiation completely according to the recent article Mars Has So Much Radiation, Any Signs of Life Would Be Buried Six Feet Under.
Research at NASA's Goddard Spaceflight Center revealed that amino acids are destroyed by cosmic rays in the Martian surface rocks and regolith at much faster rates then previously thought.
Physicist Alexander Pavlov and his team irradiated samples of amino acids mixed with minerals, simulating Martian soil, to mimic the dose of radiation expected on Mars' surface over a period of 80 million years.
It turned out that the addition of silicates greatly increased the destruction rates compared with previous experiments without them.

From the abstract of the research article:

..., amino acids and other organic molecules present in near-surface regolith and rocks on Mars can be degraded by exposure to cosmic rays that can penetrate to a depth of a few meters.

Our experimental results suggest serious challenges for the search of ancient amino acids and other potential organic biosignatures in the top 2 m of the martian surface.

Emphasis by me.

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  • $\begingroup$ It is not good to take a two month old peer reviewed article that so far has been cited only two times (one of those a self citation) as fact. Getting published in a peer reviewed journal is where science starts rather than ends. The article you referenced has not yet been confirmed or rebutted. $\endgroup$
    – David Hammen
    Commented Dec 12, 2022 at 13:37
  • $\begingroup$ @DavidHammen - Still it is the best answer so far. And it does illustrate the journey to develop the tools. The first rovers landed where there was water, but it was acidic. This rover found there was neutral water, but we need to dig deeper. The next rover will be able to dig deeper. The article mentioned a meteorite of Martian origin that contains amino acids. Here it is on Earth, but it still isn't clear if they are of biological origin. $\endgroup$
    – mmesser314
    Commented Dec 12, 2022 at 15:25
  • $\begingroup$ @DavidHammen Don't you think that especially this article was extensively reviewed by NASA since it comes from its own Goddard Spaceflight Center and because the outcome of the article could have consequences for the search for biosignatures, e.g. the sample return mission $\endgroup$
    – Cornelis
    Commented Dec 12, 2022 at 15:50
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    $\begingroup$ @Cornelis NASA has made mistakes before and has published peer-reviewed articles that have later been withdrawn. I'm not saying the article you cited is bogus. Far from it. What I am saying is that one should never take a recently published peer-reviewed article as fact. You can present such articles as highly credible conjectures. You are using this article as if it is fact, and that is what I am objecting to. $\endgroup$
    – David Hammen
    Commented Dec 12, 2022 at 20:35
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In the advent that the latest series of Mars exploration does not confirm that life once existed, or exists on Mars, it cannot be assumed that life never existed on Mars; it only decreases the likelihood that life once existed on Mars.

Exploration activities on Mars have only investigated a small number of sites on the planet. Just because evidence of life hasn't been found where we have been searching doesn't mean evidence for prior, or existing, life of Mars does not exist elsewhere.

By sending Perseverance to Jezero Crater and Curiosity to Gale Crater we are trying to improve the odds of finding life as these locations seem to have once been potentially more favorable for the presence of life. But that doesn't mean a fish bone might not be stumbled upon while we aare looking for something else in what was once the northern ocean of Mars.

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  • $\begingroup$ So on how many places do we still have to search for (past) life on Mars before we know that it never existed there ? $\endgroup$
    – Cornelis
    Commented Dec 6, 2022 at 11:29
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    $\begingroup$ @Cornelis: You can't prove a negative. But you can do exhaustive samplings once geochemists and their fancy equipment sets foot on Mars, and at some point be satisfied with enough negative results, or run out of funding for experiments. $\endgroup$
    – AtmosphericPrisonEscape
    Commented Dec 6, 2022 at 11:50
  • $\begingroup$ @AtmosphericPrisonEscape Right, but there are tens of isolated craters spread all over Mars where lakes existed and could potentially have had life, so the way things are going that will take at least a hundred years ! $\endgroup$
    – Cornelis
    Commented Dec 6, 2022 at 12:39
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    $\begingroup$ @Cornelis Can you prove that there is no teapot orbiting around the sun somewhere between Earth and Mars? At one point people looking for extraterrestrial life will realize that the hope to find life on Mars is so low that it outweighs the effort to look any further and refocus on other celestial bodies instead. Jupiter's moon Europa, for example, is another interesting candidate. $\endgroup$
    – Philipp
    Commented Dec 6, 2022 at 14:51
  • $\begingroup$ @Cornelis: Read what I wrote again. And once you have sampled all tens of thousand craters on Mars, spend hundreds of years exploring it, and all searches turned out negative, did you prove there was never life on Mars? No, you never will. The next bit of dirt might after all carry the evidence you were looking for. Ad infinitum. $\endgroup$
    – AtmosphericPrisonEscape
    Commented Dec 6, 2022 at 17:00

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