Waterworn chaos on Mars

This month, ESA’s Mars Express takes us to Shalbatana Vallis: a fascinating martian valley surrounded by signs of water, lava, craters and chaos. The institutional report frames the development in practical terms and ties it to the broader mission or observing effort.

It matters because astronomy does not advance on single detections. The field builds confidence by accumulating independent observations across different wavelengths, instruments and epochs until isolated signals become defensible conclusions. What looks convincing in one dataset can dissolve when a second instrument looks at the same target, and what looks marginal can solidify when follow-up campaigns confirm the original reading. The current standard requires that a result survive this triangulation before the community treats it as settled. 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.

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. Shalbatana Vallis formed around 3.5 billion years ago, when huge quantities of groundwater rose up to Mars’s surface.

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. 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.

This part of Mars divides the planet’s heavily cratered southern highlands (to the left) from the smoother northern lowlands (right). 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.

What gives the story weight is not just the object itself, but the way the measurement trims the range of plausible physical explanations. Astronomy has accumulated enough cases to know that the most interesting results are rarely the ones that confirm expectations cleanly; they are the ones that confirm some expectations while complicating others, or that open a parameter space that previous instruments could not reach. The scientific community evaluates these contributions by asking whether the new data constrain a model in a way that older data could not, and whether those constraints survive systematic review.

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. This image comes courtesy of the HRSC camera, one of eight state-of-the-art instruments aboard Mars Express.

Because the account originates with ESA Space News, it functions best as a primary institutional report that is close to the data and operations, not as independent scientific validation. Institutional communications are produced by organizations with legitimate interests in presenting their work in a favorable light, which does not make them unreliable but does make them partial. Details that complicate the narrative, including instrument limitations, unexpected failures and results below projections, tend to be minimized relative to progress messages. Technical documentation and peer-reviewed publications, where they exist, provide the complementary layer that institutional releases cannot substitute.

The next step is to see whether other instruments and other wavelengths tell the same story. Campaigns with JWST, the VLT, the forthcoming Extremely Large Telescopes and radio arrays will provide the spectral coverage and spatial resolution needed to move from detection to physical characterization. The timeline for that kind of confirmation is typically measured in years, not months, which is worth keeping in mind when reading the current result.

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