Chinese rover finds signs of ancient ocean on Mars

A Chinese rover has found new evidence to support the theory that Mars was once home to a vast ocean, including tracing some ancient coastline where water may once have lapped, a study said on Thursday.

The theory that an ocean covered as much as a third of the Red Planet billions of years ago has been a matter of debate between scientists for decades, and one outside researcher expressed some scepticism about the latest findings.

In 2021, China's Zhurong rover landed on a plain in the Martian northern hemisphere's Utopia region, where previous indications of ancient water had been spotted.

It has been probing the red surface ever since, and some new findings from the mission were revealed in the new study in the journal Nature.

Lead study author Bo Wu of The Hong Kong Polytechnic University told AFP that a variety of features suggesting a past ocean had been spotted around Zhurong's landing area, including "pitted cones, polygonal troughs and etched flows".

Previous research has suggested that the crater-like pitted cones could have come from mud volcanoes, and often formed in areas where there had been water or ice.

Information from the rover, as well as satellite data and analysis back on Earth, also suggested that a shoreline was once near the area, according to the study.

The team of researchers estimated that the ocean was created by flooding nearly 3.7 billion years ago.

Then the ocean froze, etching out a coastline, before disappearing a little 3.4 billion years ago, according to their scenario.

Bo emphasised that the team does "not claim that our findings definitively prove that there was an ocean on Mars".

That level of certainty will likely require a mission to bring back some Martian rocks to Earth for a closer look.

Benjamin Cardenas, a scientist who has analysed other evidence of a Martian ocean, told AFP he was "sceptical" of the new study.