As the seasons turn on Mars, the frozen carbon dioxide at the poles melts away.
Toward the end of every southern summer on Mars, parts of the vast carbon-dioxide ice cap near the planet’s south pole begin to evaporate.
Pits in the ice sheet appear and grow where the dry ice sublimates, transforming from solid to gas without becoming liquid in between.
The walls of these pits appear golden in the sunlight, though the actual makeup of the dust that gives them their colour is unknown.
This image was taken by the HiRISE camera aboard the Mars Reconnaissance Orbiter. The circular depressions in the middle of the image are about 60 metres across.