In an example of older science paying off with newer study, Curiosity discovered that some sand ripple types on Mars come from a different process from similar dune types on Earth. While studying "Bagnold Dunes" in late 2015, Curiosity imaged types of ripples on the northwestern area of Mount Sharp (Aeolis Mons). An example: Meter-sized ripples on the Martian dunes show similarities with underwater dunes on Earth. On Mars, the researchers said they believe the wind drags sand particles to create the dune shape, similar to how water moves around sand particles on Earth. "The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere," said Mathieu Lapotre, a graduate student at the California Institute of Technology who works on the Curiosity mission, in a statement. "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."
Image: Curiosity imaged two sizes of ripples in the Bagnold Dune Field. Credit: NASA/JPL-Caltech/MSSS