A bizarre, and never-before-seen kind of rippled sand dune has been discovered on Mars – and it could reveal clues about the mysterious Martian atmosphere.
The ripples, which were seen at the Bagnold Dunes, were observed by the Curiosity rover after its "first close-up study of active sand dunes anywhere other than Earth".
"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, part of the Curiosity team.
"As Curiosity was approaching the Bagnold Dunes, we started seeing the crest lines of the metre-scale ripples are sinuous," Lapotre said. "That is not like impact ripples, but it is just like sand ripples that form under moving water on Earth. And we saw that superimposed on the surfaces of these larger ripples were ripples the same size and shape as impact ripples on Earth."
The ripples also have one face steeper than the other. Another similarity between them and underwater ripples on Earth.
Researchers believe this is because the Martian wind drags sand particles "the same way flowing water drags sand particles on Earth", or what they refer to as "wind-drag ripples".
"The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere," said Lapotre. "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."
The team also noted there are many similarities between sand dunes on Mars and Earth, saying that during a visit to the dunes you could "almost forget you're on Mars". But the mid-sized ripples are "a reminder that the differences can surprise us".
Curiosity will now continue its mission to investigate ancient environmental conditions on Mars to better understand whether Mars has ever hosted life, and how conditions evolved from freshwater settings to dry, inhabitable conditions.
This article was originally published by WIRED UK
