Rolling in the crater

Seen here is a rolling rock, or a rock rolling? How did the fragmented rock (boulder) roll in this curvy fashion?

A 7-9 m boulder rolling on the Moon. Credit: NASA Lunar Reconnaissance Orbiter (LRO)

The house sized boulder is lying on a degraded crater wall, its location marked below.

Location of the rolling rock. Credit: NASA/GSFC/Arizona State University

The degraded crater wall has a downward slope. Next to the boulder location, you can see a fresh crater. When the fresh crater formed, the boulder must have been kicked out onto the degraded crater wall where it rolled down towards the crater interior. Now that’s rock and roll.

NASA’s Lunar Reconnaissance Orbiter (LRO) images have identified many such rocks rolling down (typically in a straight line). Apollo 17 Astronauts Jack Schmitt and Eugene Cernan sampled one such boulder during their Moon exploration. Tracing its source and studying the boulder allowed to infer composition of the rocks present up-slope!

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