China's Mars rover Zhurong discovers evidence supporting ancient oceans existing in Mars' mid-latitude regions

Photo shows map of Utopia Planitia, Zhurong Mars rover landing site, and four possible ancient shorelines. (Photo/Courtesy of the Aerospace Information Research Institute of Chinese Academy of Sciences)

A Chinese research team has discovered multi-layered tilted sedimentary structures beneath the surface of the Mars rover Zhurong's landing area in the northern hemisphere of Mars, which are the geological features highly similar to coastal sediments on Earth, providing the most direct underground evidence to date of the existence of an ancient ocean in Mars' mid-latitude regions, CCTV News reported on Friday.

This study extends the evidence of liquid water on Mars from its polar regions, where human activity is rare, to the mid- and low-latitude regions that are more suitable for human habitation. It confirms that Mars was once habitable, according to the media report.

The Mars radar research team led by Fang Guangyou from the Aerospace Information Research Institute of Chinese Academy of Sciences discovered those structures buried 10 to 35 meters beneath the surface of the Zhurong's landing area in the southern part of Utopia Planitia, in the northern hemisphere of Mars. The findings were published on Tuesday in the Proceedings of the National Academy of Sciences (PNAS) of the US.

Mars, with its geological features, seasonal changes, and diurnal rhythms similar to Earth, is considered by scientists as the prime candidate for human interstellar migration. Over the past few decades, many significant discoveries have been made in Mars exploration.

However, most of these findings have focused on the planet's extreme cold, high-latitude, or polar regions, and there has been ongoing debate about whether vast oceans ever existed in the northern lowlands of Mars. This has made obtaining direct evidence of Mars' ancient oceans crucial, according to the media report.

China's first Mars rover, Zhurong, landed on the southern part of Utopia Planitia on May 15, 2021.

It was equipped with the Mars Subsurface Penetrating Radar, developed by the Aerospace Information Research Institute of the Chinese Academy of Sciences to detect underground structures and potential water ice.

The rover's route was located approximately 280 kilometers north of the previously proposed ancient ocean shoreline, with an altitude about 500 meters lower than that shoreline.

By analyzing the radar's low-frequency channel data, the research team identified 76 underground tilted reflectors within a 10 to 35-meter depth range along the rover's path.

These layered structures closely resemble radar images of coastal sediments on Earth, and their consistency and physical properties rule out other possible causes, such as windblown sand dunes, lava tubes, or river alluvium.

The large-scale presence of these sediments indicates that wave-driven coastal transport provided a stable influx of mud and sand into the shoreline, forming a progradational layer that could only have formed in a large, stable water body environment, rather than from localized, short-term melting phenomena.

This research not only provides key underground evidence for the existence of ancient oceans in the northern plains of Mars, but also reveals that Mars once experienced a long period of warm, wet climate.

This suggests that Mars maintained conditions suitable for the existence of liquid water for extended periods. Moreover, the dielectric properties of the coastal sediments discovered, which are consistent with those of fine sand and medium sand particles on Earth, further confirm the oceanic nature of these sediments.

This discovery extends the evidence of liquid water on Mars from its polar regions, where human activity is rare, to the mid- and low-latitude regions that are more suitable for human habitation. It confirms that Mars was once habitable.

If an ocean once existed in this region, large amounts of water could have been stored underground as ice due to climate changes, providing potential water resources for future Mars bases and greatly reducing the costs of building and maintaining those bases.

Furthermore, these ancient ocean sediments preserve a historical record of Mars' climate changes, and studying them can help us understand how Mars transitioned from a warm and wet climate to its current cold and dry state. This, in turn, can guide human efforts to terraform Mars and achieve long-term sustainable habitation on the planet.