14-07-2025
Mars Highlands Reveal Vast 15,000 km Ancient River Network
High‑resolution images from orbiting spacecraft have revealed an extraordinary network of over 15,000 km of fluvial sinuous ridges—also known as inverted channels—spanning Noachis Terra in Mars's southern highlands. This vast system, identified using data from Mars Reconnaissance Orbiter's HiRISE, CTX and MOLA instruments, indicates long‑lasting surface water activity shaped by precipitation roughly 3.7 billion years ago, reshaping scientific views of Mars's climate evolution.
The ridges formed when river sediments cemented into resistant deposits, which later stood above the surrounding terrain after wind and erosion removed softer material. While previous research focused on valley networks, this study highlights inverted channels as compelling evidence of persistent, region‑wide water flow.
Mapping uncovers meandering tributaries branching over hundreds of kilometres, with some avenues entering craters and breaching their rims—clear signs of river systems active long enough to carve into ancient impact landscapes.
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This finds new relevance in the Noachian‑Hesperian transition around 3.7 Ga—a geological era marked by a shift to a colder, drier Mars. The extensive fluvial systems preserved in Noachis Terra suggest sustained precipitation, rather than brief warming phases, supplied the water needed to maintain these rivers over a geologically meaningful period.
The research, led by Adam Losekoot of the Open University and backed by the UK Space Agency, was unveiled at the Royal Astronomical Society's National Astronomy Meeting in Durham. Losekoot described Noachis Terra as a 'time‑capsule' recording ancient planetary processes, preserved for billions of years.
These findings challenge earlier assumptions that equated Mars's early surface with a mostly cold and icy environment, punctuated by sporadic melting events. Instead, the new evidence supports a hypothesis of a warmer, wetter environment driven by substantial precipitation over extended periods.
Noachis Terra had been relatively neglected by researchers focused on valley‑rich areas. The absence of traditional valley networks there previously led to underestimates of its water history. The focus on inverted channels opens fresh perspectives on how widespread surface water once was—even in terrains previously thought arid.
This revived understanding of Mars's hydrological past connects with other findings that hint at subsurface water reserves. Among them, a recent international study reported a potential vast aquifer beneath Mars's south polar region. The new Noachis Terra data further supports the notion that early Mars had a robust water cycle, including precipitation and possibly rain‑fed riverine systems.
Geologists also note that inverted channels have analogues on Earth, where cemented river sediments resist erosion and eventually form ridges that stand proud above eroded valleys. On Mars, such features appear most prominently in places like Miyamoto Crater and Juventae Chasma, but the scale of Noachis Terra's network is unprecedented.
The implications for Mars's early environment are significant: a hydrologically active climate may have supported ecosystems or even nascent life. Though climate modelling has struggled to produce conditions that allow sustained liquid water, the physical evidence embedded in Noachis Terra's ridges demands revised scenarios. These might include episodic atmospheric thickening or greenhouse warming phases sufficient to sustain precipitation for extended times.
Future research will likely probe whether similar inverted networks exist in other under‑studied highland regions and whether sediment composition points to seasonal cycles or sediment supply dynamics. Planned follow‑up with rover missions or crater‑site analysis may further evaluate if ancient lakes once sat behind these breached craters, and if mineral signatures—such as clay or sulphate layers—point to habitable or life‑friendly conditions.
