Ripples found on the sand dunes of Mars, often much larger than those found on similar dunes on Earth, reveal that the red planet's atmosphere is thinner than it once was, NASA said Thursday.
The Curiosity rover, which has been on Mars for almost four years, explored the Bagnold Dunes on the north-western flank of Mars' Mount Sharp six months ago, making the first ever study of active sand dunes off Earth.
NASA scientists studying Curiosity's data found that ripples on Martian dunes were in many cases much larger than those on Earth likely due to the red planet's thinner atmosphere.
The rover also found smaller ripples preserved in sandstone from more than 3 billion years ago that were closer in the size to those found on Earth. That evidence suggests Mars once had a thicker atmosphere that has since been lost.
"The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere," Mathieu Lapotre, a science team collaborator for the Curiosity mission, said.
"We think Mars had a thicker atmosphere in the past that might have formed smaller wind-drag ripples or even have prevented their formation altogether. Thus, the size of preserved wind-drag ripples, where found in Martian sandstones, may have recorded the thinning of the atmosphere."