Past research has indicated Mars’s largest northern basin, Utopia Planitia, was once the location of a large body of water, but details surrounding when this body of water may have existed have not been resolved. Researchers have now identified a ring of minerals in the region that have helped them string together a timeline of what happened there. The new study, published in Nature Communications, provides details about the ocean’s timeline and what it says about life on Mars.
Manganese oxides and hydroxides as signs of past oceans
Manganese oxides and hydroxides (collectively written as manganese (hydr)oxides) can act as geological proxies for past oceans, particularly around ancient water-air boundaries. Manganese minerals react easily with oxygen. In anoxic (oxygen-poor) water, manganese remains in its dissolved, soluble form. On the other hand, when oxygen becomes available—either through photosynthesis or atmospheric accumulation—manganese is oxidized into insoluble solid oxides, which can become signatures of water activity.
Manganese (hydr)oxides can form what are referred to as “bathtub rings” by building up at the boundary where dissolved manganese in water meets oxygen in air, forming a kind of stain along the perimeter, similar to what you might see if you leave dirty water in a bathtub for a long time and then let it drain. However, in geology, bathtub rings provide an outline of ancient shorelines. These have been identified in various regions on Earth, indicating the past presence of shallow lakes and coastal regions.
Constructing a timeline from Mars’s ‘bathtub ring’
On Mars, manganese (hydr)oxides form a distinct “bathtub ring” at specific altitudes in Utopia Planitia. The team involved in the new study analyzed short-wave infrared (SWIR) data from China’s Zhurong rover, ESA’s OMEGA orbiter and NASA’s CRISM orbiter to identify and quantify manganese (hydr)oxides. They designed a deep learning model called Spectral Contrastive-Aware Network (SCANet) to capture the diagnostic features of manganese (hydr)oxides. They then had the model analyze 5,781,762 Martian SWIR spectra.
The analysis showed that concentrations of manganese (hydr)oxides increased with altitude, rising from 2.7 wt% to 7.4 wt% over a range of about 10 meters. Above this, they dropped off. The team says the placement of the ring indicates that the ring formed during the Hesperian epoch—a geologic period on Mars that occurred roughly 3.7 to 3.0 billion years ago. The Hesperian epoch marked the transition from the warmer, wetter, and volcanically active Martian world to a cold, dry, and dusty planet.
The study authors write, “Overall, the spatiotemporal distribution of MnOx offers a reliable indicator of critical transitions in the evolution of surface aqueous environments over time on Mars. It reveals that the Hesperian–Amazonian transition (~3.0 billion years ago) likely disrupted habitable surface water environments due to increased volcanic activity in Utopia Planitia, marking a critical point in Mars’s geological history when the potential for further prebiotic evolution on the surface was significantly reduced.”
The team says that over time the ocean dried up, and this is visible through the regression of the concentration of manganese (hydr)oxides deposits along the shorelines. Ultimately, they calculated that the ocean lasted around 0.8–1.5 million years.
“This yields a final estimated duration of 0.8–1.5 million years for the presence of stable aqueous conditions in Utopia Planitia. This timescale significantly exceeds what is typically expected for transient surface water activity on Mars, suggesting that Utopia Planitia hosted a long-lived and evolving aquatic system during the Hesperian epoch, rather than a short-lived or rapidly evaporating water body,” write the study authors.
Potential for life in the past—and the future
The researchers say that although this does not provide direct evidence of early life, it does suggest that Mars may have provided an environment conducive to initiating early forms of life. The timeline of the ocean matches the minimal timescale required for prebiotic chemistry, and also temporally overlaps with the period on Earth in which scientists believe the earliest forms of life first arose, approximately 3.4 billion years ago.
The study authors also note that the conditions for life may have also extended into the next Amazonian period on Mars. They write, “If MnOx formation or redistribution occurred during the Amazonian, this would suggest that Mars may have maintained episodic or localized liquid water environments significantly later than traditionally assumed.”
Interestingly, the authors also bring up the potential for future human habitation on Mars. They suggest that oxygen can be produced by using the manganese (hydr)oxides for water-splitting reactions that generate oxygen through photocatalysis, potentially supporting human activities or even terraforming. Of course, this would be a long way off.
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Publication details
Bingxu Hou et al, Manganese (Hydr)oxides record the dynamic evolution of a million-year Hesperian Ocean in Utopia Planitia, Mars, Nature Communications (2026). DOI: 10.1038/s41467-026-72858-y
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Mars’s manganese ‘bathtub ring’ reveals ancient ocean timeline and its potential for life (2026, May 29)
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