"As Curiosity was approaching the Bagnold Dunes, we started seeing that the crest lines of the meter-scale ripples are sinuous," said Lapotre, who's also science team collaborator for the Curiosity mission. "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."
So it turns out that Mars dunes have an added complexity that could only be proven by rolling up close and taking photos. Mars dunes have the small impact ripples, plus medium-sized "sinuous ripples" that can be resolved from space.
RELATED: The Mysteries Behind the Dunes of Mars
Interestingly, though Earth's dunes don't possess sinuous ripples, they can form underwater -- on a riverbed, for example. Rather than particles colliding, these sinuous ripples are created as flowing water drags particles, causing them to settle in a rippled pattern.
Lapotre, who is lead author of a study that was published on July 1 in the journal Science, thinks that the Martian sinuous ripples are being driven in a similar way, but it's the Red Planet's thin atmosphere that's dragging the particles to form the medium-sized ripples on the sand dunes. Lapotre's team have nicknamed them "wind-drag ripples."