AM: Drilling on Earth is a notoriously dirty process, where you contaminate the subsurface with surface materials and other things.Sorry, I still think there's going to be significant cross-contamination between the layers, rendering the results of any studies the lander does of the various soil layers less definitive than we'd like to see from an organization like NASA!CM: That’s not an issue for planetary protection, because they’re only concerned about contaminating Mars with stuff from Earth. But in terms of mixing the materials -- that will happen if we drill. We’ll form a pile of material around the drill hole, and that will be mixed with material from various depths. But we’ll still be able to get samples from known depth even while we’re making a mess around the drill. We’ll drill, then bring the drill up and clean it, and then send it back down and drill for a little bit, and then bring it up again. The stuff that’s on the drill at that point will be from that known depth, and we can study it.
They’ll do better to keep the layers separate when they drill core samples. Digging is little more than what most dogs can do.
Altering the chemistry of our landing site due to our thruster exhaust is unavoidable. The Phoenix Lander uses hydrazine, a hypergolic propellant that turns into ammonia during combustion. So essentially, we are spraying the surface with ammonia and a small amount of hydrazine that was not combusted. The way we get around that is by 1) knowing that we are going to be producing ammonia and 2) by designing the wet chemistry cells to carefully quantify the amount of ammonia in the regolith. We then use this information to interpret our other results.