NASA’s Mars Reconnaissance Orbiter captured this intriguing view of “corduroy” sand dunes rippling across the permanent polar cap of Mars. The dunes “march across a fabric of patterned ground,” according to a NASA caption that explains “at this time of the Martian year the dunes are free of the seasonal dry ie that forms a temporary cover every winter.” Launched in 2005, the MRO braked into orbit around the red planet in 2006 to study the history and distribution of water. Its High Resolution Imaging Science Experiment, or HiRISE, which took the image seen here, is one of the most powerful cameras ever launched aboard a planetary spacecraft.
Mars hasn’t always looked like it does today. Some 3 to 3.5 billion years ago, the planet underwent a huge tilt of 20 to 25 degrees. The gigantic Tharsis volcanic dome, which started to form over 3.7 billion years ago, grew so massive that it caused Mars’ crust and mantle to swivel around, shifting the Tharsis dome to the planet’s equator.