Mars today is a cold, dry, dusty planet with its only obvious water locked up in frozen polar ice caps. But billions of years ago, it appears to have had sandy beaches lapped by waves along the shoreline of a vast ocean.
The evidence for beaches on Mars comes from a Chinese rover, called Zhurong, that landed on the planet in 2021. During its short life it detected evidence of underground beach deposits in an area thought to have once been the site of an ancient sea, bolstering the idea that the planet long ago had large bodies of water.
During it’s one year of operation, between May 2021 and May 2022, Zhurong traveled 1.9 kilometers (1.2 miles) roughly perpendicular to escarpments thought to be an ancient shoreline from a time — 4 billion years ago — when Mars had a thicker atmosphere and a warmer climate. Along its path, the rover used ground penetrating radar (GPR) to probe up to 80 meters (260 feet) beneath the surface. This radar is used to detect underground objects, such as pipes and utilities, but also irregular features, such as boundaries between rock layers or unmarked graves.