This feels very cynical, but what incentive does NASA have to do research showing alien life is not very likely in our solar system?
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I.e.: they don’t carry high power microscopes because apparently there’s no room for one on a 900kg rover the size of a car.
A good enough microscope can easily tell the difference between life and non-life, especially in the presence of water. If it moves on its own, it is almost certainly alive!
Certain kinds of chromatographs can conclusively determine that no complex chemicals are present, the kind essential to life. I.e.: if only simple metal oxides and the like are present, then you have only a rock.
NASA (and also the Soviet Union and ESA) have repeatedly designed Mars sample return missions, but have not done them for budgetary reasons; it would be tremendously difficult and expensive.
Here's the current one: https://en.wikipedia.org/wiki/NASA-ESA_Mars_Sample_Return - however, given that it was hitting funding problems even _before_ ol' minihands gutted NASA funding, it seems destined to become yet another NASA/ESA canceled program (there's a bit of a history of ambitious NASA/ESA collaborations which die when one side or the other pulls the budgetary plug; JWST was likely lucky to escape this fate, say).
This puts it in a particularly weird place, as the earth return section is already built and due to launch on an Ariane 6 in two years (it will then proceed, slowly, to Mars using an ion drive, and await the lander and Mars launcher, which will presumably never arrive because budgets).