A quake on Mars may have set these rocks rolling

Now there’s solid evidence marsquakes can send boulders tumbling, too. Scientists mined high-resolution imagery of the Red Planet taken shortly after a recent temblor and found hundreds of new imprints left by tumbling boulders, researchers report September 2 in npj Space Exploration. Such rockfalls can be used as a proxy for seismic data, which is difficult to collect across the solar system.

The data were collected with NASA’s InSight lander, which touched down on Mars in 2018. Over the next four years, its seismometer detected more than a thousand marsquakes. Many of those temblors originated in a region known as Cerberus Fossae, just north of the Martian equator.

That’s a dynamic landscape riddled with slopes, cracks and rocks on the move, says Vijayan, a planetary scientist at the Physical Research Laboratory in Ahmedabad, India, who goes by a single name. By comparing images taken in June 2019 and December 2020, the researchers discovered 27 new linelike features. Each was composed of tens to hundreds of distinct marks.

These structures were most likely tracks created by boulders bouncing downhill, the team concluded. Using historical imagery, the researchers calculated that only about two such features form each year on average in Cerberus Fossae. Recording 27 new structures over a span of just 18 months is wholly unexpected, Das says.

Mysteries remain, however. All of the rockfalls occurred on the north side of a prominent valley in Cerberus Fossae, despite more boulders being located on the south side of the valley. The complex landscape of Cerberus Fossae might well alter how seismic waves travel, making it difficult to predict how shaking will impact different areas, he says.

Human settlements would do best avoiding areas that are seismically active, and tumbling boulders can be the proverbial canaries in the coal mine, Vijayan says.