June 30, 2016
Some of the wind-sculpted sand ripples on Mars are a type not seen on Earth, and their relationship to the thin Martian atmosphere today provides new clues about the atmosphere’s history.
The determination that these mid-size ripples are a distinct type resulted from observations by NASA’s Curiosity Mars rover. Six months ago, Curiosity made the first up-close study of active sand dunes anywhere other than Earth, at the “Bagnold Dunes” on the northwestern flank of Mars’ Mount Sharp.
“Earth and Mars both have big sand dunes and small sand ripples, but on Mars, there’s something in between that we don’t have on Earth,” said Mathieu Lapotre, a graduate student at Caltech in Pasadena, California, and science team collaborator for the Curiosity mission. He is the lead author of a report about these mid-size ripples published in the July 1 issue of the journal Science.
Both planets have true dunes — typically larger than a football field — with downwind faces shaped by sand avalanches, making them steeper than the upwind faces.
Earth also has smaller ripples — appearing in rows typically less than a foot (less than 30 centimeters) apart — that are formed by wind-carried sand grains colliding with other sand grains along the ground. Some of these “impact ripples” corrugate the surfaces of sand dunes and beaches.