Peering down on Mars, a distant NASA satellite captured curious lines crisscrossing a Martian crater.
There's no doubt these are natural tracks left by Martian dust devils, the High Resolution Imaging Science Experiment (HiRISE) research team at the University of Arizona told Mashable. HiRISE is the powerful camera aboard NASA's Mars Reconnaissance Orbiter, the satellite capturing rich imagery of the red planet's evolving surface.
Dust devils often whirl over the Martian ground. "Dust devils on Mars form the same way as they do on Earth," HiRISE, who recently posted the image online, explained. This happens when the ground grows warmer than the air, heating the air above it. Updrafts rise while cooler air then sinks down, creating vertically circulating air. Dust devils on Mars, however, can be much larger than those on Earth.
By comparing past images of dunes in the crater below, HiRISE scientists can be certain dust devils formed the tracks, as opposed to boulders tumbling over the terrain. (Dust devils can spin quite vigorously on the ground, leaving clear evidence of their travels.)
Dust devil tracks inside a Martian crater. Credit: NASA / JPL-Caltech / University of Arizona 
A closer view, in color, of dust devil tracks inside a Martian crater. Credit: NASA / JPL-Caltech / University of Arizona SEE ALSO: Strange, unexpected things are happening on Neptune Compelling Mars photo shows Martian water flowed way more recently than we think
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NASA's satellite captured these dust devil tracks in Eastern Aonia Terra, a well-cratered area in Mars' southern hemisphere.
Elsewhere on Mars, car-sized robots are leaving unnatural tracks on the ground. One of these machines, NASA's Perseverance rover, is now exploring a dried-up river delta in the desert planet's Jezero Crater, a place that once teemed with water billions of years ago. The Perseverance rover is seeking past evidence of long-dead, primitive life in the delta's ancient sediments.
"If Mars did host life during this time, remnants or signatures of those organisms could be preserved in some of these ancient rocks," the space agency noted in a blog.
Today, Mars' frigid, inhospitable surface is lifeless. But dust devils still whirl over the Martian plains, and through its colossal craters.
