Valles Marineris is a vast canyon system that runs along the Martian equator just east of the Tharsis region.
It is 4,000 km (2,500 miles) long and reaches depths of up to 7 km (4 miles) — roughly 10 times longer and 5 times deeper than the Grand Canyon in Arizona.
It comprises myriad smaller rifts, channels, outflows, fractures and signs of flowing material (such as water, ice, lava or debris).
Valles Marineris is an unmissable scar on the face of Mars, and thought to have formed as the planet’s crust was stretched by nearby volcanic activity, causing it to rip and crack open before collapsing into the deep troughs we see today.
These troughs have been further shaped and eroded by water flows, landslides, and other erosive processes, with spacecraft including Mars Express spying signs that water existed in parts of Valles Marineris in the relatively recent past.
The new image from Mars Express’ HRSC instrument shows ‘chaotic terrain’ in Pyrrhae Regio — a region located south of Eos Chasma, an eastern branch of the Valles Marineris system.
A scattering of impact craters, formed as incoming bodies from space collided with Mars’ surface, can be seen to the left of the frame.
The floor of the largest and uppermost basin spans about 40 km (25 miles), and contains some fractures and markings that formed just after the crater itself.
Hot, molten rock is thought to have been thrown up during the crater-forming collision, after which it cooled and settled to form the scar-like features visible here.
Towards the middle of the frame, the surface is relatively smooth and featureless — however, two broad channels have worked their way through the landscape, and can be seen as meandering, branching indentations in the surrounding terrain.
The valleys are attached at their rightward end to the real star of the image: a sunken, uneven, scarred patch of ground known as chaotic terrain.
Chaotic terrain, as the name suggests, looks irregular and jumbled, and is thought to form as sub-surface ice and sediment begins to melt and shift.
This shifting layer causes the surface above to collapse — a collapse that can happen quickly and catastrophically as water drains away rapidly through the Martian regolith.
Ice can be triggered to melt by heating events such as volcanic lava flows, subsurface magmatism, impacts by large meteorites, or changes in climate.
In the chaotic terrain seen here, ice has melted, the resulting water drained away, and a number of disparate broken blocks have been left standing in now-empty cavities.
Remarkably, the floors of these cavities lie some 4 km (2.5 miles) below the flatter ground near the craters to the left.