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While petrified sand dunes can be found in the American Southwest, these ones were spotted a little farther from home — on the lower slopes of Mount Sharp on Mars.
Captured in late August by NASA's Curiosity rover, this image shows a layer of sandstone that researchers are calling the "Stimson unit." It sits over a layer of mudstone, which was deposited there long ago in a "lake environment."
NASA believes they formed much like petrified sand dunes on Earth, created by blowing winds and then cemented into rock.
Later this month, NASA plans to use Curiosity to drill into the Stimson unit and analyze some of the sandstone, hopefully learning something about Mars' geographic past.
The rover reached Mount Sharp late last year after touching down on the Martian surface in 2012. In the two weeks since taking the photo, it has traveled more than 300 feet.