Ice ages are an entirely separate phenomenon to more recent human-caused global warming. They are part of an ancient geological rhythm primarily caused by changes in a planet’s path around the Sun and the wobble of its rotational axis. During an ice age, ice is more widespread in the form of glaciers and ice sheets, and fluctuating temperatures enable flows of ice to advance and retreat across the globe.

We see the telltale signs of previous ice ages on other planets, too – their impact on modern-day Mars is evident in these new images from the High Resolution Stereo Camera on ESA’s Mars Express.

The roughly parallel lines slicing diagonally through the image are known as Coloe Fossae, a feature created as alternating chunks of ground fell away. Many craters, formed as incoming space rocks collided with the surface, are seen here: large, small, overlapping, irregular, clustered, older and more recent, both well-defined and smoothed away by erosion. On the floors of the valleys and craters is something exciting: patterns of swirling lines that indicate where material flowed during a previous martian ice age.