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This image from the UA-operated HiRISE camera on NASA's Mars Reconnaissance Orbiter shows linear gullies extending almost 1.2 miles inside Russell Crater. Unlike gullies caused by water-lubricated flows on Earth and possibly on Mars, they don't have apron (Photo: NASA/JPL-Caltech/UA) This image from the UA-operated HiRISE camera on NASA's Mars Reconnaissance Orbiter shows linear gullies extending almost 1.2 miles inside Russell Crater. Unlike gullies caused by water-lubricated flows on Earth and possibly on Mars, they don't have aprons of debris at the downhill end of the channel, just an empty pit – most likely left behind by dry-ice chunks.