- Mars once had an ocean, new evidence suggests. The findings supports a growing number of other studies with the same conclusion. But this study strongly suggests the ocean once filled Valles Marineris, the Grand Canyon of Mars.
- Researchers found ancient deltas in the Valles Marineris canyon system. They appear to have been formed by rivers that flowed into the ocean along an ancient shoreline.
- The ocean was at least as large as the Arctic Ocean on Earth and covered about half of Mars, researchers say.
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More evidence for an ancient Mars ocean
Evidence continues to mount for a long-lost ocean on ancient Mars. Several studies in the past few years have supported that scenario, and now a new study bolsters the idea. An international team of researchers, led by the University of Bern in Switzerland, spoke on January 12, 2026, about newly noticed ancient deltas in the vast Valles Marineris canyon system. They say these deltas lie along what used to be the coastline of a Mars ocean in this planet’s northern hemisphere. The researchers say the ocean was at least as large as the Arctic Ocean on Earth and that it covered about half of Mars.
The researchers found the deltas in images taken by various Mars orbiters, including ExoMars Trace Gas Orbiter, Mars Express and Mars Reconnaissance Orbiter. The deltas are located in southeast Coprates Chasma, which is part of the immense Valles Marineris canyon system.
The new peer-reviewed findings were published in NPJ Space Exploration on January 7, 2026.
University of Bern: Mars Was Half Covered by an Ocean mediarelations.unibe.ch/media_releas…
— AAS Press Office (@press.aas.org) 2026-01-12T16:58:11.295Z
Old river deltas in Valles Marineris
In the new study, the researchers focused on Coprates Chasma, which is in the southeastern portion of the Valles Marineris canyon system. They used high-resolution images from the orbiters to examine the geological structures in this region.
Ignatius Argadestya is a Ph.D. student at the Institute of Geological Sciences and the Physics Institute of the University of Bern. He said:
The unique high-resolution satellite images of Mars have enabled us to study the Martian landscape in great detail by surveying and mapping.
This is when they found the deltas. Argadestya continued:
When measuring and mapping the Martian images, I was able to recognize mountains and valleys that resemble a mountainous landscape on Earth. However, I was particularly impressed by the deltas that I discovered at the edge of one of the mountains.
The deltas, known as scarp-fronted deposits or delta fans, were at the lower end of the canyon system. On Earth, they are formed by rivers that empty into standing bodies of water. Such deltas have been found elsewhere on Mars too, including in Jezero crater, where NASA’s Perseverance rover is currently exploring. As Fritz Schlunegger, Professor of Exogenous Geology at the Institute of Geological Sciences at the University of Bern explained it:
Delta structures develop where rivers debouch into oceans [editor’s note: where rivers flow out from a narrow, confined channel or valley into a wider, open area], as we know from numerous examples on Earth.
An ocean that covered half of Mars
The deltas are further evidence for a vast ocean that once existed in the northern hemisphere of Mars. Schlunegger said:
The structures that we were able to identify in the images are clearly the mouth of a river into an ocean.
Previous studies have suggested that the ocean once covered much of Mars’ northern hemisphere. The new study supports that. In fact, it says that the former ocean was at least as large as the Arctic Ocean on Earth, and covered about half of Mars. That’s huge, especially when you consider that Mars is only about half the size of Earth. As Schlunegger noted:
We are not the first to postulate the existence and size of the ocean. However, earlier claims were based on less precise data and partly on indirect arguments. Our reconstruction of the sea level, on the other hand, is based on clear evidence for such a coastline, as we were able to use high-resolution images.
Life on a blue planet?
So, if there was an ocean, was there also life? We don’t know yet, but having an ocean, lakes and rivers certainly shows that Mars was indeed much more habitable than it is today. Argadestya said:
We know Mars as a dry, red planet. However, our results show that it was a blue planet in the past, similar to Earth. This finding also shows that water is precious on a planet and could possibly disappear at some point.
As the paper concludes:
Our research thus provides a further documentation of the time span where availability of liquid water on the surface was the highest during the evolution of this planet. We thus consider that our findings on the environmental stage during the Late Hesperian to Early Amazonian will have implications for research on the evidence for potential life on Mars.
Bottom line: Evidence for an ancient Mars ocean keeps growing. Deltas in the Valles Marineris canyon along the former shoreline show that the ocean covered half the planet.
Source: Scarp-fronted deposits record the highest water level in Mars’ Valles Marineris
Via University of Bern
Read more:
New evidence for ocean on Mars found in ancient rivers
Vacation-style beaches on Mars? New evidence for lost ocean
More evidence for ancient ocean on Mars from Chinese rover