image: A moderately eroded fluvial sinuous ridge (FSR), with lots of small craters in it, that stands out clearly above the surrounding material. To the north east it emerges from a small valley and becomes progressively clearer to the west, until it disappears. There is a clear curve in the FSR, likely a meander. North of the FSR is a round, flat feature that was likely an impact crater which was filled with water or sediment. CTX image: MurrayLab_V01_E020_N-20_Mosaic
Credit: NASA/JPL/MSSS/The Murray Lab
Royal Astronomical Society press release
RAS PR 25/30 (NAM 10)
9 July 2025
Embargoed until Thursday 10 July 2025 at 00:01 BST
The discovery of more than 15,000 kilometres of ancient riverbeds on Mars suggests that the Red Planet may once have been much wetter than previously thought.
Researchers looked at fluvial sinuous ridges, also known as inverted channels, across Noachis Terra – a region in Mars' southern highlands. These are believed to have formed when sediment deposited by rivers hardened and was later exposed as the surrounding material eroded.
Similar ridges have been found across a range of terrains on Mars. Their presence suggests that flowing water was once widespread in this region of Mars, with precipitation being the most likely source of this water.
The new research, led by Adam Losekoot – a PhD student at the Open University, funded by the UK Space Agency – is being presented today at the Royal Astronomical Society's National Astronomy Meeting 2025 in Durham.
The findings indicate that surface water may have been stable in Noachis Terra during the Noachian-Hesperian transition, a period of geologic and climatic change around 3.7 billion years ago.
Noachis Terra has not been studied as extensively as other regions of Mars, in part because it contains few valley networks, which are branching erosional features that have traditionally been used to infer historical rainfall and runoff.
The study instead focuses on fluvial sinuous ridges as an alternate form of evidence for ancient surface water.
"Studying Mars, particularly an underexplored region like Noachis Terra, is really exciting because it's an environment which has been largely unchanged for billions of years. It's a time capsule that records fundamental geological processes in a way that just isn't possible here on Earth," said Losekoot.
He and his team used data from three orbital instruments: the Context Camera (CTX), the Mars Orbiter Laser Altimeter (MOLA) and the High Resolution Imaging Science Experiment (HiRISE).
These datasets allowed the team to map the locations, lengths and morphologies of ridge systems across a wide area.
Many of the features appear as isolated ridge segments, while others form systems extending for hundreds of kilometres and rising tens of metres above the surrounding terrain.
The broad distribution and form of these ridges suggest that they likely formed over a geologically significant period under relatively stable surface conditions.
The spatial distribution and extent of the features indicate that the water source was precipitation.
"Our work is a new piece of evidence that suggests that Mars was once a much more complex and active planet than it is now, which is such an exciting thing to be involved in," said Losekoot.
The fact that the ridges form extensive interconnected systems suggests that the watery conditions must have been relatively long-lived, meaning Noachis Terra experienced warm and wet conditions for a geologically relevant period.
These findings challenge existing theories that Mars was generally cold and dry, with a few valleys formed by ice-sheet meltwater in sporadic, short periods of warming.
ENDS
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Science contacts
Adam Losekoot
Images & captions
A moderately eroded fluvial sinuous ridge (FSR), with lots of small craters in it, that stands out clearly above the surrounding material. To the north east it emerges from a small valley and becomes progressively clearer to the west, until it disappears. There is a clear curve in the FSR, likely a meander. North of the FSR is a round, flat feature that was likely an impact crater which was filled with water or sediment. CTX image: MurrayLab_V01_E020_N-20_Mosaic
Credit: NASA/JPL/MSSS/The Murray Lab
Two east-west branches of an FSR. These preserve an area where a river split and then rejoined (off image). The lower branch is heavily eroded and quite spread out, the upper branch is narrower but more clearly preserved. These may have been exposed for different amounts of time, undergone different geological processes, or represent different periods of river activity. There are remnants of an infilling material within the ridge and a meander where the branch turns back towards the lower trunk. Between the two branches is a kind of mesa, this may be a pedestal of harder material or a crater that was filled in with the same material as the FSRs.
Credit: HiRISE Image: ESP_085519_1585 NASA/JPL/University of Arizona
Branch of an FSR in HiRISE in a merged IRB image. Horizontal layers clear in the side of the main ridge and channel infill present on top of the ridge. The layers are evidence of the ridge material being formed by sediment in a river environment.
Credit: HiRISE Image: ESP_084451_1585 NASA/JPL/University of Arizona
Merged IRB image of a narrow FSR with a pointed top (pinnacle ridge) and a meander. The pointed top may show that this FSR has been eroded heavily for a long time until only a narrow peak remains, or it may be that only a narrow part of the original river infill has been preserved. Credit: HiRISE Image: ESP_067439_1505 NASA/JPL/University of Arizona
Colour image of a flat top, heavily eroded FSR. Sand dunes can be seen migrating over the top of the FSR.
Credit: HiRISE Image: ESP_085386_1505 NASA/JPL/University of Arizona
Oblique view of part of a system of FSRs, recording multiple river tributaries, likely all active at the same or similar times. This shows rivers meandering, areas where river banks have burst and fine layers of sediment have been deposited around the river, and branching. At the top of the image is a really clear example of an area where two FSRs intersect with an infilled crater. This is likely where the river flowed into the crater, filling it up and then breaching the other side to continue through the crater and down to the bottom of the image. CTX image: MurrayLab_V01_E020_N-20_Mosaic
Credit: NASA/JPL/MSSS/The Murray Lab
Further information
The talk 'The Fluvial History of Noachis Terra, Mars' will take place at NAM at 17:12 BST on Thursday 10 July 2025 in room TLC116. Find out more at: https://conference.astro.dur.ac.uk/event/7/contributions/607/
If you would like a Zoom link and password to watch it online, please email press@ras.ac.uk
- The Context Camera, called CTX, provides a big-picture, background view of the terrain around smaller rock and mineral targets that are studied by other cameras on Mars Reconnaissance Orbiter. CTX makes observations simultaneously with high-resolution images collected by HiRISE and data collected by the mineral-finding CRISM spectrometer.
- The High Resolution Imaging Experiment is known as HiRISE. It takes pictures that cover vast areas of Martian terrain while being able to see features as small as a kitchen table, and has photographed hundreds of targeted swaths of Mars' surface in unprecedented detail. The camera operates in visible wavelengths, the same as human eyes, but with a telescopic lens that produces images at resolutions never before seen in planetary exploration missions. These high-resolution images enable scientists to distinguish objects on Mars about 3 feet (1 metre) and to study the morphology (surface structure) in a much more comprehensive manner than ever before.
- The Mars Orbiter Laser Altimeter (MOLA) was an instrument on the Mars Global Surveyor (MGS) spacecraft that mapped the topography of Mars using laser altimetry. It operated from September 1997 to June 2001, collecting data on the height of surface features. This data was used to create detailed topographic maps and study the planet's geology and past climate.
Notes for editors
The NAM 2025 conference is principally sponsored by the Royal Astronomical Society and Durham University.
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