Mystery of Mars' Perfectly Circular Sand Dunes Baffles Scientists

NASA's Mars Reconnaissance Orbiter captured images of almost perfectly circular sand dunes on the Red Planet's northern hemisphere. While sand dunes of all shapes and sizes are common on Mars, circular dunes like these are a rare sight. The steep sides of the dunes are slanted southward, which might be due to Martian winds blowing the sand in that direction. However, scientists are unsure what caused the dunes to be so near-perfectly circular. The image is part of a series taken by HiRise to help monitor how frost melts on Mars at 60 different locations as the northern hemisphere of the planet reaches the end of its winter season.