These images taken by the Mars Reconnaissance Orbiter’s HiRISE camera, which has exquisitely high resolution, show avalanches off the layered icy terrain near Mars’s north pole. Noticed by HiRISE team member Ingrid Spitale, wife of my Cassini ring scientist colleague Joe Spitale, these slides are part of Mars’s seasonal changes which are more extreme than the Earth’s. Like Earth, Mars’s rotation axis is tilted relative to its orbital axis resulting in more direct sunlight on one hemisphere than the other for half of a Martian year. Unlike the Earth, however, Mars’s orbit is significantly elliptical, meaning that it is closer to the Sun during summer in the Southern hemisphere making it particularly warm, and further from the Sun during northern summer. It is currently northern summer on Mars, and these avalanches are a product of the seasonal breakup of the ice on the north polar cap. The martian polar caps consist of water ice underneath carbon dioxide ice (“dry ice”).
Context image showing two plumes of dust caused by material falling down the face of Mars’s polar ice caps.