NASA’s Mars Reconnaissance Orbiter (MRO) acquired this image of Martian dunes almost free of their seasonal ice cover in the early summer. Only pockets of ice protected in the shade most of the day remain.

The North Pole of Mars is surrounded by a vast sea of sand dunes. In this dune field, the dunes are covered by a seasonal cap of dry ice in the winter. In Mars’ northern hemisphere, the snow and ice speckling the landscape is made not of water, but carbon dioxide.

Frozen carbon dioxide, better known as dry ice, requires temperatures of about minus 193 degrees Fahrenheit (minus 125 Celsius), which is much colder than needed for freezing water. Carbon-dioxide snow reminds scientists that although some parts of Mars may look quite Earth-like, the Red Planet is very different.