It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
On Mars, by contrast, dunes are made up mostly of dark, dense minerals like olivine, from volcanic basalt. The dunes get darker with time as finer dust, which contains lighter-colored feldspar minerals, blows away.
Zooming in on the western (top in the main colour image) portion of the crater reveals distinct layers of dark material exposed in the crater walls. One possible interpretation is that the impact crater punched through the top surface to reveal these otherwise hidden layers. Over time, this material has been eroded and swept up by wind to form the dunes seen towards the centre of the crater.
Researchers conclude that the meter-scale ripples are built by Martian wind dragging sand particles the way flowing water drags sand particles on Earth -- a different mechanism than how either dunes or impact ripples form. Lapotre and co-authors call them "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," he said.