Here are a couple press conferences that summarize what Perseverance has found so far.
- Press conference: Ten months of Perseverance: Jezero science
- News Briefing: NASA's Perseverance Mars Rover Investigates Geologically Rich Area (Sept. 15, 2022)
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?
@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?
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?