PSP_001756_1995_1.0xA piece of Mars: In the center are two dark dunes, racing one another to jump over hurdles formed of older, now inactive dunes (or maybe those bright things are ripples, we still don’t know for sure). The dune in the lead has been slowed by this barrier, but it is starting to crawl over it, one sand grain at a time. The dune in second place is still well-formed but will likely struggle once it runs into its own hurdle. Perhaps 20 years from now. (PSP_001756_1995, NASA/JPL/University of Arizona)

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