Thanks
I feel better already. I know these boys are clever enough to have thought of this already, as they must have also done so for the Mariner landings decades ago. But I still fear that if we apply a known stress (hydrazine exhaust) to an unknown quantity (Martian polar soil), we may get totally unexpected and misleading experimental results.
Still, I'm aware that we really didn't have much choice in the matter, and the fact that better minds than mine have already considered the problem and taken steps to mitigate it does reassure me somewhat.