As Perseverance rattles off to Mars, he goes through five possibilities at Forbes:
Mars never had life.
Life died out.
Life persisted beneath the surface
Earth seeded life on Mars
The space program spread life to Mars
It’s the ultimate nightmare of astrobiologists: that there’s a fascinating history of life to uncover on another world, but we’ll contaminate it with our own organisms before we ever learn the true history of life on that world. In the worst case scenario, it could be the case that was surviving simple life on Mars of Martian origin, but that Earth life arrived and out-competed it, driving it to a rapid extinction. This very real, healthy fear is why we’re frequently so conservative, from a biological perspective, when we explore other planets and foreign worlds.Ethan Siegel, “The Five Possibilities for Life on Mars” at Forbes
Well, we’re so conservative that we haven’t actually explored any other planets and foreign worlds recently …
Interesting reading though.