For the past few years, tantalizing evidence has been found that Mars — thought to be long dead, dry, and lifeless — may have pockets of water just beneath the surface. To be clear, we know there’s water on Mars, in the form of ice. We see ice in the polar caps, and we’ve seen it revealed under the surface by small meteorite impacts.

The question is, is there liquid water?

New images by the Mars Reconnaissance Orbiter bring us a step closer to answering that question. A series of pictures of the 300 km (180 mile) wide Newton crater taken over the course of several years show dark deposits on the crater wall which change predictably with the seasons, clearly affiliated with some sort of material flowing downslope:

[Click to barsoomenate.]

The picture above shows Newton’s crater wall. It’s pretty steep, with about a 35° slope, and the dark deposits are labeled. This crater is located in the southern mid-latitudes of Mars, and this part of the crater faces north. That’s critical! Since it faces toward the equator, that means it’s facing the Sun in the summer, and so these deposits appear when ...