Solved: The Mystery of The Walking Martian Rocks

Rocks on Mars are on the move, rolling into the wind and forming organized patterns, according to new research.

Images taken by the Mars Exploration Rover Spirit show small rocks regularly spaced about 5 to 7 cm apart on the intercrater plains between Lahontan Crater and the Columbia Hills.

The new finding counters the previous explanation of the evenly spaced arrangement of small rocks on Mars. That explanation suggested the rocks were picked up and carried downwind by extreme high-speed winds thought to occur on Mars in the past.

Pelletier and his colleagues suggest that wind blows sand away from the front of the rock, creating a pit, and then deposits that sand behind the rock, creating a hill. The rock then rolls forward into the pit, moving into the wind, he said. As long as the wind continues to blow, the process is repeated and the rocks move forward.

These Spirit Rover camera images of the intercrater plain between Mars' Lahontan Crater show uniformly-spaced small rocks, known as clasts. Credit: GSA

The process is nearly the same with a cluster of rocks. However, with a cluster of rocks, those in the front of the group shield those in the middle or on the edges from the wind. Because the middle and outer rocks are not directly hit by the wind, the wind creates pits to the sides of those rocks. Therefore, they roll to the side, not directly into the wind, and the cluster begins to spread out.

Pelletier plans to apply the same models to larger features on Mars such as sand dunes and wind-sculpted valleys and ridges called "yardangs." press release

Ref.: Wind-Driven Reorganization of Coarse Clasts on the Surface of Mars. 2008. Geology

NASA Mars Exploration Rover Mission