Mars' north polar cap swirls like a slowly melting ice-cream cake. Hidden within the layers is a record of the seasons, as polar ice disappears in summer and reappears in winter. The record is as old as the layers are deep, like the pages of a history book.
To learn what ancient Mars was like, scientists use radar to turn a penetrating gaze beneath the surface. Dustier layers appear white because they reflect radar waves; icier layers appear black because they're transparent. Just as Earth scientists read tree rings to document climate change, Mars scientists study buried ice.
The scalloped mountain of ice is more than a mile high. At its base are flatter, less transparent layers. Are these layers ancient sand deposits from a time when Mars' climate was different? The answers will only be revealed with radar studies of every dip and fold of the changing polar cap.
Shallow Subsurface Radar, Mars Reconnaissance Orbiter
Image credits: NASA/ESA/JPL-Caltech/ASI/University of Rome/University of Washington St. Louis
