Last week when scientists revealed dramatic new pictures of flood-like gullies on Mars, the big surprise wasn’t that the Red Planet might harbor water. Researchers have known for years that water exists there. There are trace quantities of water vapor in Mars’ atmosphere and substantial amounts of water ice at the martian poles. There may even be enough frozen water beneath Mars’ surface to fill a large ocean if melted. What was amazing is that water may be present as a liquid very near the planet’s surface and occasionally on top of the surface when underground deposits burst forth for a brief flash flood.