In a study recently published in the National Science Review, a team of researchers led by the China University of Geosciences discuss direct evidence for an ancient ocean and its shoreline that existed in the northern hemisphere of Mars during the Hesperian period, more than three billion years ago . This finding is based on data collected by the China National Space Agency (CNSA) Zhurong rover in the Vastitas Borealis Formation (VBF), located in southern Utopia Planitia on Mars.
The Zhurong rover landed in Utopia Planitia on May 15, 2021 after being ferried from Earth to Mars by the Tianwen-1 orbiter, which is still active around the Red Planet. Originally designed for a mission duration of 90 sols (93 Earth days), Zhurong has far exceeded this time frame. However, Zhurong went into hibernation in May 2022 (Sol 347) to protect itself from the harsh Martian winter. Although the plan was to resume communications with the CNSA in December 2022, this did not materialize and the CNSA recently acknowledged that this could potentially be gone for good.
During its mission, Zhurong has traveled 1,921 meters (6,302 ft), or just under 2 kilometers (1.24 mi), and its altitude has decreased by about 5 meters (16.4 ft). During this hike, researchers used Zhurong’s multispectral camera (MSCam) to perform in situ analyzes of 23 rocks from 106 pairs of panoramic images, and the observations Zhurong made were impressive.
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a) Basemap of the satellite imagery HiRIC (HX1_GRAS_HIRIC_DIM_0.7_0004_251515N1095850E_A) (Figure 1 of the study); b) HiRISE DEM (DTEEC_069665_2055_069731_2055) overlaid on the HiRIC. The red star marks Zhurong’s landing site, with the rover traveling nearly 2 kilometers (1.24 miles) between its landing site and Zhurong’s last known location (Sol_344), with an elevation difference of approximately 5 meters (16.4 feet). (Source: ©Science China Press)
“When we examined the photos returned by these cameras, we found that these exposed rocks had distinct layered structures that were quite different from the common volcanic rocks on the Martian surface or the layered structures formed by wind-blown sand deposits,” said dr Xiao Long, a professor in the School of Earth Sciences at China University of Geosciences and lead author of the study. “These layered structures indicate the properties of bidirectional water flow consistent with the low-energy tidal currents observed in terrestrial coastal environments on Earth.”
Essentially, the study used the rover’s images to uncover evidence of an ancient shoreline that featured tides on Mars. It revisits many previous studies that attempted to plot ancient Martian shorelines using orbiter data, with this mission being the first to conduct such direct in situ analysis of the subject.
Elevation map of the northern hemisphere of Mars with the red star marking the landing site of the rover Zhurong, which is approximately 282 kilometers (~175 miles) north of a previously proposed coastline of the ancient Deuteronilus Ocean. The different colored lines represent proposed coastlines from previous studies. (Source: ©Science China Press)
On Earth, due to our moon’s gravitational pull, tides step both in front of and behind the coast. Because Mars has two moons, researchers suspect these tides may still exist in the ancient ocean, albeit on smaller scales.
The sedimentary structures observed in the images support the hypothesis that these structures were formed by water currents and not by wind deposition. The researchers also conclude that these sedimentary structures could also have formed during a major retreat of an ancient ocean during the Hesperian period.
Like Earth, the geological history of Mars is divided into distinct epochs, also known as periods: Noachian, Hesperian, and Amazon. It is estimated that the Noah period took place 4.1 to 3.7 billion years ago, the Hesper period 3.7 to 2.9 billion years ago and the Amazon period started 2.9 billion years ago and lasts until today on. Although a pre-Noahian period from 4.5 to 4.1 billion years ago has been identified and debated in the scientific community, no direct evidence for its existence has been found.
Artist’s rendering of an ancient northern ocean on Mars billions of years ago. (Credit: NASA/Goddard Space Flight Center)
With these incredible findings from the Zhurong rover, scientists are gaining new insights into the history of Mars and how much different it might have looked billions of years ago than the cold and arid planet it is today.
“Future exploration and sample return missions in this region will further deepen our understanding of the habitability of Mars and the preservation of traces of life,” said Dr. Long.
Both NASA and China have drawn up numerous plans for a sample-return mission from Mars, as the former is working with the European Space Agency (ESA) to bring Martian samples back to Earth by 2033, and China has announced a timeline to bring samples back in 2031 and you exceed the effort of NASA/ESA by two years. NASA’s Perseverance rover recently began collecting samples, dropping sample tubes full of Martian regolith and pebbles to be collected later by a sample-return mission that’s currently one step ahead of China.
What new discoveries will scientists make about ancient Mars and its ancient shores in the coming years and decades? Only time will tell, and that’s why we do science!
As always, keep up the science and keep looking up!