Eternal Darkness of Petronius Crater
Near Mercury's north and south pole, the sun is always low on the horizon. Long sunsets and sunrises are broken only by long nights. But for impact craters near the poles, no sunlight ever directly reaches the crater floor due to the long shadows cast by the crater rim. Petronius crater, seen in today's featured image, is one such region of permanent shadow, and is also known to host radar-bright deposits, thought to be water ice.
Date acquired: September 21, 2012
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington