Would you mind elaborating on this? I don’t understand the point. Maybe naively, I would think that evidence of life on mars would increase the probability of life on exoplanets.
The more common that life is, the more likely it is in front of us.
We can't know or even begin to guess at what an alien civilization may do or think or how they evolved. Best we can do is assume it's probably somewhat similar to our experience. At least it's based on something factual. Anything else is really just wild speculation.
We pretty much have to assume aliens will be sort of similar to us because we haven't met any. Our experience is the only one we've got, so it's the most reasonable baseline we have. We know that aliens will probably be wildly different from us, but it's so unknowable as to be moot. Do we base our assumptions on Heinlein's writing? Asimov? Douglas Adams? Anything other than what we know from our own experience is just fanciful fiction.
But also you're not supposed to take as read the Fermi paradox, Kardashev scale, or any other ways of thinking about aliens. It's implied that they won't be anything like us. You're not supposed to take it as a literal statement that alien species will be hairless bipeds with a warlike society who think and look like us. You're supposed to follow the assumptions that statistically, we're probably not special as a species and probably any aliens we meet will have evolved along similar lines and probably will be relatable to us. Implicitly we understand that this likely is not true. We just don't know and there aren't really any options that are more reasonable or reliable than basing assumptions on the one and only planet we know that has intelligent life.
As in, different stars may encourage slightly different chemical reactions and interactions on their planets.
Like, for example, could it be possible for a planet to form with a naturally highly magnetized mineral in its crust? Would it affect the rest of the chemistry on the planet? Would it cause the ground to interact with its star's magnetic envelope, like our atmosphere within the Auroras does?
In fact, this makes the preoccupation with humans escaping a Great Filter all the more childish. Even on a single planet the species that will evolve from humans by the time Earth is swallowed by the sun will have less in common with humans than we do now with single cell organisms. Internalize that fact a little bit. Once you realize it is absurd to talk about the human species being preserved as is to the end of time, you will understand the silliness of this obsession. Cause after that point you might as well believe in a deity.
If it makes you feel warm and fuzzy inside, it suffices to hope that only single cell organisms survive the Great Filter, since given enough time it might lead to something that is as intelligent or more intelligent and kind than humans.
Embrace the silliness. The answer to "Why should we humans spread to other planets?" need only be "Why the fuck not?"
That is, unless you want to fund your rocket company. In which case you have to make people believe in a deity.
If this isn’t true, and life is actually common throughout the galaxy ... then the great filter might still be ahead of us — such as not surviving technological adolescence. Meaning we’re not special, we just haven’t died off yet.
Great filters start with the observation that we have detected no signs of alien technological civilization. The assumption is this means they’re rare.
In other words, even if the average technological civilisation lasts 1000 years, the odds of those civilisations overlapping are nearly zero if the great filter is ahead of us. Unless civilisations manage to last much, much longer than 1,000 years (millions of years), the chance that two blips overlap in time and space closely enough to detect each other is basically negligible.
That is why the “life on Mars” point feels ominous:
- If abiogenesis is easy, the filter isn’t there.
- If the filter is later (like surviving technological adolescence), then most civilisations blink out quickly.
Which means overlapping, detectable civilisations would be vanishingly rare, explaining the silence, but also suggesting our future may be short.
Personally I think the great filter is a dumb idea for precisely the reason you posit. The universe is (probably) infinite, which means there's an infinite probability that we aren't special or alone. Maybe we're the first; the universe is (relatively) pretty young from what we can tell. I doubt that too, but I think it's one of the most plausible explanations.
But really what it comes down to is that in an infinite universe, the probability of anything happening exaxtlt once is infinitely small. It is infinitely more probable that there is or will be other life out there.
Really, out of uncountable trillions of planets in trillions of galaxies across tens of billions of years, how could it be that exactly one planet can produce life? I think it's egotistical navel-gazing in the extreme to assume we're alone.
We aren’t special. We will die off.
And of course nothing is ruling out life in the nooks and crannies of Mars.
The big problem is that the solar wind strips away the atmosphere and water, but that's (probably) not what killed all Martian life. As the magnetic field decreases, more and more harmful radiation reaches the surface. The planet was probably sterilized by radiation long before the atmosphere was lost and the oceans evaporated.
We're pretty sure this is what happened. We've been studying Mars's geology for a long time and we can see evidence for most of this process.