The long-serving Martian rovers have come out of winter hibernation in style with Spirit discovering proof of explosive volcanic eruptions some time in Mars's past. While it may seem obvious, Martian volcanoes are primarily (maybe even exclusively) basaltic, whose eruptions are not normally explosive. Liquid water can make basaltic eruptions go "boom" via steam, so this seems to be yet another confirmation that liquid water once existed on the Martian surface.