New evidence based on data collected by China's Zhurong rover proves an ancient ocean was once present on Mars, said new research published in the academic journal National Science Review on Thursday.

Led by Professor Xiao Long from the School of Earth Sciences, China University of Geosciences (Wuhan), the researchers conducted comprehensive analysis of the scientific data obtained by the cameras mounted on the Zhurong rover.

The rover, which was launched in 2021, landed on the southern margin of the Utopia Planitia, a vast plain on the northern hemisphere of Mars.

The location is within Vastitas Borealis Formation (VBF), a lowlands-wide sedimentary unit, "whose outer contact closely coincides with the features interpreted as a shoreline," providing an opportunity to verify the existence of ancient marine sediments, according to the research.

Though previous research has extracted evidence for the presence of an ocean in the northern lowlands of Mars, the lack of in-situ data of the VBF has left it controversial.

Thanks to Zhurong, the researchers carried out the first in-situ analysis of the VBF.

In its voyage of roughly 1,921 meters, the Zhurong rover had traveled southward towards the proposed shoreline since landing, exploring the surface exposures of the VBF along the way.

It deployed different imaging and analysis systems to conduct in-situ observations of outcrops and surface rocks. Among them, the navigation and terrain cameras acquired 106 sets of panoramic images, recording in detail the surface sedimentary structures and features of the rocks in the vicinity of the route.

By observing the images sent back by the rover-borne cameras, the researchers found the exposed rocks have developed bedding features that are significantly different from the volcanic rocks commonly found on the Martian surface or the typical aeolian deposits, but are similar to those seen in terrestrial low energy shallow marine environments.

The sedimentary structures and features in surface rocks suggest the VBF "was deposited in a marine environment," providing direct support for the existence of an ancient ocean on Mars, said the researchers, adding that the deposition of the sedimentary rocks in the landing site of Zhurong occurred during the regressional period of an Hesperian ocean.

The discovery provides new implications for reshaping the history of Mars. "Future in-depth exploration and sampling of the region by Zhurong will deepen our understanding of Mars' habitability and the preservation of life traces there," said Xiao.