Mars has a number of relatively young volcanoes
As I recall from a news item not too long ago, Olympus Mons as
one example last erupted perhaps 3 million years ago, and there
is speculation that volcanic activity is still going on there somewhere.
Was Phoenix outfitted with a seismometer, and if not, why not?
What we need are a bunch of small seismic (and weather) stations
dropped all over the planet. Technology miniaturization is improving,
so this is a feasible idea. One big probe to one area of a planet just
doesn't cut it any more.