The European Space Agency (ESA) has once again treated us to a spectacular view from the Red Planet, this time returning to the fascinating region known as Acheron Fossae. Through the lens of the Mars Express probe, which has been tirelessly orbiting Mars for more than two decades, we have gained a new, more detailed insight into the western edge of this geologically extremely active region. This is a landscape that bears witness to the ancient and turbulent past of our planetary neighbor, a place where dramas of epic proportions unfolded, leaving behind scars visible even after billions of years.

This area is not unknown to scientists. Back in April 2004, just a few months after Mars Express began its mission, the first images of Acheron Fossae were published, intriguing the global public. We recently had the opportunity to see the eastern part of the region, and the latest data now reveal equally stunning formations on the western edge, where deep canyons, valleys, and winding channels intertwine, shaped by the slow but powerful flows of ice and rock.

Geological Drama on the Edge of a Volcanic Giant

Acheron Fossae represents an exceptionally complex system of tectonic trenches, or faults in the Martian crust. These formations, known as fossae, create a characteristic relief that geologists call a "horst and graben" system. Simply put, it is a pattern where uplifted blocks of the crust (horsts) alternate with down-dropped blocks (grabens). Looking at the images, this pattern is most obvious in the pronounced channels that run vertically through the central part of the frame, creating the impression of a broken and fractured terrain.

It is believed that this dramatic landscape was formed more than 3.7 billion years ago, during a period when Mars was geologically much more active than it is today. The cause of its formation lies deep beneath the surface. A powerful uplift of hot material, or magma, from the Martian mantle towards the crust created immense pressure. This led to the stretching and cracking of the crust, resulting in the formation of kilometers-deep fissures and valleys, some of which stretch for hundreds of kilometers in length. This process is closely linked to the formation of the vast volcanic highland of Tharsis, on whose northern edge Acheron Fossae is located. Nearby, although some 1200 kilometers to the south, is Olympus Mons, the largest volcano in the entire Solar System, whose activity undoubtedly influenced the tectonics of the entire region.

Traces of Ice and Climate: A Story Written in the Valleys

Once these monumental valleys were created, their transformation did not cease. A bird's-eye view, generated from data from the HRSC camera, reveals that the floors of these valleys are relatively smooth and filled with material that shows subtle, winding lines. They are irresistibly reminiscent of a river's flow, but here it was not water that flowed in liquid form. Instead, the valleys are filled with what geologists call rock glaciers.

These are slow, viscous flows of a mixture of ice, dust, and rock debris. Similar formations exist on Earth, mainly in high mountain and polar regions. Rock glaciers are extremely sensitive to climate change and are therefore excellent indicators of how a planet's environment has changed over time. Their presence in Acheron Fossae clearly indicates that this region of Mars has experienced alternating periods of colder and warmer conditions – cycles of freezing and thawing.

These dramatic temperature fluctuations on Mars are primarily caused by changes in the tilt of its rotational axis. Unlike Earth, whose tilt is relatively stable thanks to the gravitational influence of our large Moon, Mars has no such "stabilizer." Because of this, its axial tilt varies drastically over long periods of time. In the last 10 million years, Mars's tilt has ranged from 15 to 45 degrees, while Earth's has only changed between 22 and 24.5 degrees. These periodic changes, known as Milankovitch cycles, also play a key role in our planet's climate, but their effects on Mars are far more pronounced, causing alternations between warm periods and true ice ages. During these ice ages, ice could spread far from the poles, covering areas closer to the equator, just like Acheron Fossae.

Erosion and Remnants of an Ancient Landscape

On the right side of the image, the system of trenches gradually transitions into flat, dark lowlands. Between them is a belt of rugged terrain composed of rounded hills (knobs) and steep plateaus with flat tops (mesas). These formations are actually remnants of a once-uniform layer of rock. Over eons, the slow but relentless flows of ice and rock eroded and carried away the softer material, leaving behind only the more resistant, isolated uplands. Today, they stand out from the plain as witnesses to a formerly higher terrain level.

This transition – from deep tectonic trenches, through eroded hills and mesas, to vast lowlands – is particularly noticeable on the region's topographic map. On it, red and yellow tones mark higher areas, gradually blending into lighter and darker shades of blue that represent lower elevations. To the left of the image, another area of smooth plain is visible. This is terrain located near the aforementioned volcanic giant Olympus Mons, and its smooth surface is likely the result of volcanic ash deposition and lava flows during its turbulent history.

The Eye of Mars Express: More Than Two Decades of Exploration

The Mars Express mission of the European Space Agency is crucial to our understanding of the Red Planet. Since its launch in 2003, this orbiter has been imaging and studying the diverse landscapes of Mars, providing scientists with invaluable data. The probe has mapped nearly the entire surface of the planet in color, with unprecedented resolution and, most importantly, in three dimensions. It is precisely this 3D data that allows for the creation of detailed topographic maps and realistic flyovers, drastically changing our understanding of our planetary neighbor.

The key instrument for such feats is the High Resolution Stereo Camera (HRSC), developed and operated by the German Aerospace Center (DLR). Systematic data processing is carried out at the DLR Institute of Planetary Research in Berlin, while the Planetary Sciences and Remote Sensing working group at the Freie Universität Berlin has used this data to create the fascinating image products we have the opportunity to see today. Every new image, like this one from the edge of Acheron Fossae, is not just a beautiful "postcard," but a piece of a giant puzzle that helps us reconstruct the geological evolution of Mars, the role of water and ice in its past, and the changing nature of its climate.