Did Mars once have an ocean? Scientists have new evidence

Billions of years ago, the Red Planet may have been covered by water over as much as one third of its surface, according to a new study by scientists from the American university Caltech. The likelihood that an ocean once existed on Mars sheds new light on the discussion about extraterrestrial life and sets targets for future exploration missions.

Earth as a reference

As early as the mid-1960s, the American probe Mariner 4 succeeded in capturing the first images of the surface of Mars. In the following decades, probes landing on the Red Planet provided new data revealing a diverse topography. Scientists identified canyons, volcanoes, and eventually also significant deposits of ice.

So far, however, little has been known about the forms in which water once accumulated on Mars. Dr Abdallah Zaki and Prof Michael Lamb from Caltech decided to analyze available topographic data in an attempt to reconstruct the Martian hydrosphere from billions of years ago. They used observations of Earth as a reference.

Using complex computer simulations, the researchers virtually drained Earth’s oceans to examine what the landscape would look like without them. It turned out that the most characteristic evidence of their existence is not the shorelines but continental shelves, flat bands of land up to several hundred kilometers wide, also known as shelves. They surround oceans at depths ranging from 15 to 400 m like a ring, marking the boundary with land.

An ocean on Mars – very likely

After applying insights from Earth’s topography to data obtained from Mars, it turned out that a similar ring of shelves can be distinguished in the northern hemisphere of the Red Planet. It lies at depths between 1800 and 3800 m and very likely marks the boundaries of a former ocean. In some places, this unusual terrain could admittedly be explained by the presence of solidified lava flows, but the rounded shape of the Martian shelves rather points to a large body of water.

Additional evidence supporting the existence of an ocean on Mars comes from river deltas identified by scientists, triangular sediment zones that logically surround the belt of flat areas. Within the presumed shelf, coastal deposits, thick sequences of layered rock, and minerals altered by water have also been observed.

Is colonization of the Red Planet possible?

NASA and SpaceX announce that in the fourth decade of the 21st century they aim to land humans on Mars, and Elon Musk even speculates about building a self-sustaining city. At present, however, real physical obstacles stand in the way of possible colonization: an atmosphere composed mainly of carbon dioxide, extremely low pressure, high levels of radiation, and temperatures hovering around -60°C.

The problem of water resources essential for life is expected to be addressed by vast amounts of ice, which scientists believe are hidden beneath the surface of the Red Planet. Some sources suggest that if melted, they could cover the entire planet with a shallow ocean. In addition, there is speculation about the presence of temporary layers of salty water that do not freeze as easily.

A challenge for the future is to confirm the availability and usability of these resources, which could be used not only for drinking and food production, but also for producing oxygen and rocket fuel. The possible colonization of Mars, even if it were indeed feasible, is a task for many decades. For now, there is nothing left but to treat Earth with the respect it deserves and to take care of the water we have, which continues to diminish in many regions.

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Source:
Zaki, A.S., Lamb, M.P. Identifying the topographic signature of early Martian oceans. Nature 652, 878–885 (2026). https://doi.org/10.1038/s41586-026-10381-2