Chinese rover finds further evidence for an ancient ocean on Mars

A possible ancient shoreline has been found in the region of Mars explored by the Chinese rover Zhurong, providing further evidence that an ocean may once have covered a vast area of the lowlands in the planet’s northern hemisphere.

The rover landed in southern Utopia Planitia in May 2021 and remained active for almost a year. Researchers studying data from the rover have found hints of an ancient ocean or liquid water as recently as 400,000 years ago.

Now, Bo Wu at Hong Kong Polytechnic University and his colleagues have conducted a comprehensive analysis of the topographic features in the landing area, combining remote sensing data from satellites with observations from the rover.

They say they have found features consistent with the existence of a shoreline in southern Utopia, including troughs and sediment channels. They also dated and identified the composition of surface deposits in the area. Based on this, the team thinks the ocean existed 3.68 billion years ago, but froze and then disappeared around 260 million years later.

“The findings not only provide further evidence to support the theory of a Martian ocean but also present, for the first time, a discussion on its probable evolutionary scenario,” says Wu.

The area can be divided into a shallow section to the south and a deep section in the north. Even the shallow part of the ocean may have been up to 600 metres deep, says Wu, but there isn’t enough data to estimate the maximum depth of the ocean.

“Water is a key ingredient for life, and the past presence of an ocean on Mars raises the prospect that Mars once might have been capable of harbouring microbial life at its early stage,” he says.

Mathieu Lapôtre at Stanford University in California says whether oceans existed on early Mars is a highly contentious question with critical implications for the planet’s past habitability. He says future missions will need to test the findings of this new research.

“Utopia Planitia may constitute an invaluable record of early Mars’s near-shore and coastal environments,” says Lapôtre.