China’s Zhurong rover.
Credit: CNSA

China’s robotic Mars rover has revealed new information about its landing zone, Utopia Planitia, the largest basin on Mars.

That site may well be the location for China’s projected Tianwen-3 mission dedicated to Mars sample return by the end of the decade.

In the just-published work, the country’s Zhurong Mars rover made use of onboard radar and detected irregular wedges (polygons) underneath its exploration zone.

The Chinese researchers are proposing that the polygons were potentially generated by freeze-thaw cycles. That interpretation implies that there was a strong palaeoclimatic variability at low-to-mid latitudes (roughly 25° North), possibly due to the high obliquity of ancient Mars.

Illustration of the scientific payloads mounted on Zhurong rover. The group picture of the rover (left) and the lander (right) was taken by the WiFi camera (Image Credit: the ChinaNational Space Administration (CNSA)). NaTeCam: Navigation and Terrain camera. RoMAG: Mars Rover Magnetometer. MSCam: Multispectral Camera. MSC-1: MarsClimate Station (Wind field and sound probe). MSC-2: Mars Climate Station (Air
temperature and pressure probe). MarSCoDe: Mars Surface Component Detector. RoPeR(CH1): Mars Rover Penetrating Radar (channel 1). RoPeR (CH2): Mars Rover
Penetrating Radar (channel 2).
Image credit: Steve Yang Liu, Et al.

The research – “Buried palaeo-polygonal terrain detected underneath Utopia Planitia on Mars by the Zhurong radar” – has been published in a new issue of Nature Astronomy and led by Lei Zhang of the CAS Engineering Laboratory for Deep Resources Equipment and Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing, China.

In-depth research

The polygonal wedges were radar detected below a depth of 35 meters within the rover’s journey of approximately 1.2 kilometers, according to the study.

The lander, carrying the rover with an expected life span of at least 90 Martian days or about three months on Earth, touched down in the southern part of Utopia Planitia on May 15, 2021.

Launched in July 2020, China’s Tianwen-1 mission consisted of an orbiter, a lander and a rover. The Zhurong rover was deployed by the lander after touching down in the southern part of Utopia Planitia on May 15, 2021.

Topographic map of Utopia Planitia, showing the landing sites of the Zhurong rover, the Viking 2 lander and the Perseverance rover. The elevation contour is shown. Four local regions (c–f) with polygonal terrain are marked with white squares. b, The Zhurong rover traverse from Sol 11 through Sol 113. Green segments denote the wedges of buried polygons recognized from. Purple segments denote the interiors of the polygons. Image credit: Lei Zhang, et al.

Water/ice freeze?

According to the research paper, sixteen polygonal wedges were identified within roughly 1.2 kilometers distance, suggesting a wide distribution of such terrain under Utopia Planitia. These detected features probably formed on ancient Mars and were buried by later geological processes.

Lei and colleagues went through a process of elimination focused on cause of the buried polygons.

The buried palaeo-polygonal terrain requires a cold environment, they report, “might be related to water/ice freeze–thaw processes in southern Utopia Planitia on early Mars.”

a, The origination of thermal contraction cracking on the surface of Mars. b, The formation of cracks in-filled by water ice or soil material, causing three types of polygonal terrain (ice-wedge, composite-wedge and sand-wedge polygons). c, The stabilization of the surface polygonal terrain in the Late Hesperian–Early Amazonian, possibly with the cessation of an ancient wet environment. d, The palaeo-polygonal terrain, either with or without being eroded, was subsequently buried by deposition of the covering materials in the Amazonian. The Mars surface image was acquired by the Navigation and Terrain Camera (NaTeCam).
Image credit: Lei Zhang, et al.

The detected buried polygons indicate that freezing occurred at low-to-mid latitudes and requires strong palaeoclimatic variability, potentially due to the higher obliquity of Mars than today.

“The possible presence of water and ice required for the freeze–thaw process in the wedges may have come from cryogenic suction-induced moisture migration from an underground aquifer on Mars, snowfall from the air or vapor diffusion for pore ice deposition,” the paper explains.

Mars return sample site?

While not discussed in the research paper, China has outlined a plan that calls for launching a Mars sample return mission in 2028, snag specimens of the martian surface, and rocket those materials to Earth, perhaps as early as July 2031.

Such an undertaking mirrors, in large measure, return sample knowhow exhibited at the Moon in 2020 by the country’s Change’-5 lunar mission.

A return to the Utopia Planitia area, surveyed in detail by the Zhurong rover (now thought expired), could well be on tap.

To access the Nature Astronomy paper published November 23 – “Buried palaeo-polygonal terrain detected underneath Utopia Planitia on Mars by the Zhurong radar” – go to:

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