Waterworn chaos on Mars

Shalbatana Vallis is an impressive channel near Mars’s equator. This image, taken by Mars Express’s High Resolution Stereo Camera (HRSC), captures the northern part of the channel, which weaves its way across Mars’s surface for some 1300 km – around the length of Italy.

We visited this part of the Red Planet in October 2025, releasing a Mars Express video journey that followed this gently meandering channel from its beginning (the highland region of Xanthe Terra) to its end (the smoother lowlands of Chryse Planitia).

Shalbatana Vallis formed around 3.5 billion years ago, when huge quantities of groundwater rose up to Mars’s surface. These catastrophic floodwaters cut into the rock and surged downhill, rapidly creating the winding, waterworn valleys we see here. The main valley, which snakes in from the bottom-left and weaves out of frame to the right (north), is about 10 km wide and 500 m deep – something seen most clearly in the associated topographical view (below).

Rough meets smooth

Shalbatana Vallis was likely deeper in the past, but has been filled in over time with different materials. While we don’t know exactly which materials filled the valley, one isolated patch of more recently deposited blue-black material can be seen in the most knobbly part of the channel: volcanic ash blown about by martian winds, as shown in the accompanying 3D perspective views (below, and further down).

Shalbatana Vallis is one of many such valleys found in this region. This part of Mars divides the planet’s heavily cratered southern highlands (to the left) from the smoother northern lowlands (right). Just out of frame lies the aforementioned Chryse Planitia, one of the lowest parts of the entire planet (see map below). Many of Mars’s largest outflow channels end at Chryse Planitia, leading some to suggest that it may have once been covered by a sizeable ocean at some point in Mars’s warmer, wetter history.

Chaos and craters

Many other intriguing features can be seen here, all of which are labelled on the annotated view of Shalbatana Vallis.

Outflow channels are usually found alongside something named chaotic terrain, a labyrinthine jumble of raised blocks and mounds of rock. Chaotic terrain can be seen here in the wider part of Shalbatana Vallis, near the dark layer of volcanic ash (see below). It’s thought to form as water ice trapped below the surface begins to melt, causing the ground above to shift and ultimately collapse. This kind of terrain is common on Mars, and has been captured before by Mars Express in regions such as Pyrrhae Regio, Iani Chaos, Ariadnes Colles, Aram Chaos and – in video form – Hydraotes Chaos.

Many impact craters can also be seen here. Some are buried, some worn away, and some surrounded by blankets of material thrown out during the initial crater-forming collision. Overall, the terrain is relatively smooth, indicating that it has been flooded by lava; in places this lava crumpled and folded as it cooled and shrunk, forming irregular ‘wrinkle ridges’. Isolated hills (‘mesas’) can also be seen (to the upper right, for example) – remnants of a once-higher surface that has been worn away over time.

Decades of Mars exploration

This image comes courtesy of the HRSC camera, one of eight state-of-the-art instruments aboard Mars Express. Mars Express has been capturing and exploring Mars’s many landscapes since it launched in 2003. The orbiter has mapped the planet’s surface at unprecedented resolution, in colour, and in three dimensions for over two decades now, returning insights that have fundamentally changed our understanding of our planetary neighbour (read more about Mars Express and its findings here).

The Mars Express HRSC was developed and is operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The systematic processing of the camera data took place at the DLR Institute of Space Research in Berlin-Adlershof. The working group of Planetary Science and Remote Sensing at Freie Universität Berlin used the data to create the image products shown here.