NASA's Mars Reconnaissance Orbiter satellite just shot this image of rippling, evenly-spaced steps leading down into four craters in the Arabia Terra region of Mars. What causes such regularity in the shapes of these rocks?

Apparently the pattern created by these "steps" corresponds to a known pattern in the tilt of Mars' rotational axis. So these perfectly-spaced ridges were created during periodic changes in the planet's tilt.

Martian Rock with Ten Beats to the Bar [via NASA]

Photo via NASA and AP.