Exploring the Canyons and Cliffs of Mars SpaceDaily

In the first three installments of this series, I described the current theories now being offered to explain Surveyor’s remarkable discovery of what looks very much like recent eruptions of liquid groundwater onto Mars’ surface — and in the coldest, most unlikely parts of the planet imaginable. There are at least five theories bouncing around at the moment (in two of which the stuff erupting isn’t even water, but carbon dioxide).