A Chinese rover has found new evidence supporting the theory that Mars was once home to a vast ocean, including tracing an ancient coastline where water might once have flowed, according to a study released Thursday.

The theory that an ocean covered up to a third of the Red Planet billions of years ago has been debated among scientists for decades, and one outside researcher has expressed some skepticism about the latest findings.

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

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

The study’s lead author, Bo Wu, from the Hong Kong Polytechnic University, said: AFP that a variety of features suggestive of a past ocean had been spotted around the Zhurong landing zone, including “pitted cones, polygonal troughs, and etched flows”.

Previous research has suggested that the crater-shaped pitted cones may have originated from mud volcanoes and often formed in areas where there was water or ice.

Information from the rover, as well as satellite data and analysis on Earth, also suggests that a shoreline once stood 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, carving out a coastline, before disappearing a little 3.4 billion ago, according to their scenario.

Bo emphasized that the team “does not claim that our findings definitively prove that there was an ocean on Mars.”

This level of certainty will likely require a mission to bring Martian rocks back to Earth for closer examination.

The coast is always changing

Benjamin Cardenas, a scientist who has analyzed other evidence for the existence of a Martian ocean, said AFP he was “skeptical” about the new study.

He felt that researchers had not sufficiently taken into account the strength of the Martian wind that had blown around sediments and worn rocks over the past billion years.

“We tend to think that Mars is not very active, like the Moon, but it is active!” said Cardenas of Pennsylvania State University in the US.

He pointed to previous modeling research that suggested that “even slow erosion rates on Mars” would destroy signs of a coastline over such a long period.

Bo acknowledged that the wind may have worn away some rocks, but said the impact of meteors hitting Mars can also “excavate underground rocks and sediments to the surface from time to time.”

Although the overall theory remains controversial, Cardenas said he tends to “think there was an ocean on Mars.”

Discovering the truth could help solve a bigger mystery: Is Earth the only one in the solar system capable of supporting life?

“Most scientists believe that life on Earth originated either beneath the ocean, where hot gases and minerals from underground reach the seafloor, or very close to the interface between water and the ocean. air, in small tidal basins,” Cardenas said.

“So the evidence of an ocean makes the planet look more hospitable.”