A Song of Ice and Tectonics

Many craters in the mid-latitudes of Mars are partially filled with deposits that have been interpreted to be ice-rich. We expect the deposits to have formed at an earlier (but relatively recent) time when Mars' orbital parameters were different and allowed ice to condense and deposit in these locations. The ice is covered by dust layers protecting it from sublimating away. The ice deposits are probably no older than a few million years, which is recent in geological terms.