ESA’s Mars Express Discovers Deep Valleys and Frozen Features Hinting at Mars’ Icy Past

The European Space Agency's Mars Express has been mapping Mars for over 20 years. In July 2025 it sent back a high-resolution image of the Acheron Fossae region – a rugged area cut by deep chasms and valleys. It's layout of ridges and sunken valleys has long intrigued researchers. The new photo examines the western edge of this region, giving a closer look at the fascinating topography found here. Scientists are hopeful of unravelling Mars's geologic history from studying these images as those features are indicative of how the Red Planet's surface was shaped over time.

Orbiter Reveals Mars' Chasms and Valleys

According to the new Mars Express images of the Acheron Fossae, these long faults (called fossae) run through the region, splitting the ground into alternating high blocks and low blocks. The raised blocks (horsts) and sunken troughs (grabens) form a pattern like a stretched crust. In the valley floors, the ground is relatively smooth, filled by slow-moving flows of ice-rich rock (often called rock glaciers). Over time, these icy flows carved the terrain into rounded hills (knobs) and flat-topped plateaus (mesas). In short, the orbiter's photo shows Mars's surface marked by deep scars and shaped by ancient flows of ice and rock.

Geological History

These features offer clues to Mars's long history. The deep scars likely formed about 3.7 billion years ago, during Mars's most geologically active era. Back then, molten rock rising under the crust stretched and pulled apart the surface. Later, as Mars cooled, ice mixed with rock flowed into these valleys like very slow glaciers. These “rock glaciers” carved the valley floors smooth and built up knobs and mesas. Because rock glaciers form in cold climates, their presence suggests Mars once had cycles of ice ages.