Mars moon Phobos grooves formed by rolling boulders, study suggests

A new study suggests that the enigmatic grooves on the surface of Mars' moon Phobos were formed by boulders rolling across the moon after an ancient asteroid impact. The research, published in Planetary and Space Science, uses computer models to simulate the movement of debris from Stickney crater, the largest feature on Phobos.

The study, led by Ken Ramsley of Brown University, builds on a long-standing hypothesis that the grooves were carved by ejecta from the Stickney impact. The models show that boulders ejected from the crater could have created the patterns seen today, despite some inconsistencies in their alignment.

Phobos, which measures 27 kilometers at its widest point, has grooves that have puzzled scientists for decades. Some theories suggest that the grooves were formed by impacts on Mars or by the moon's gradual disintegration due to Mars' gravity. However, the rolling boulder model has gained traction, especially after the recent simulations.

The simulations revealed that due to Phobos' weak gravity, boulders could roll for long distances, even circumnavigating the moon. This explains why some grooves are not radially aligned with Stickney and why some are superposed on others. The models also accounted for the absence of grooves in a specific low-lying area, which acts like a natural ski jump, causing boulders to leap over the region.