Well, we've found evidence of 'life on mars' haven't we? Fossilized bacteria? Am I misremembering?
They found a meteorite that had pretty definitely been knocked off Mars, and inside it they found . . . thingies. Said thingies looked somewhat like fossilized bacteria, but they were way too small. The options, as I understand them, are:
(1) they are a genuine Martian life-form—although maybe not a whole lot like Earth bacteria, because microbiologists have no idea how you could cram a whole bacterium, or even bacterium-like life-form, into that small a space, or . . .
(2) they're inorganic anomalies that happen to look a whole lot like fossilized bacteria through sheer coincidence.
As I understand it, the scientific community is leaning toward explanation two. Gotta admit it's simpler.
There is, however, a
lot of evidence for water on Mars—flowing water—a lot more than there is now. So I'd say past life is a pretty good possibility. (Actually, I think current life is still a possibility, in isolated pockets. Nothing multicellular, though.)
Izunya