China’s Zhurong Rover Found These Mysterious Polygonal Structures Under the Martian Soil. They May Be More Common Than We Thought

Apart from Earth, of course, Mars is undoubtedly the planet that attracts the most attention. The more than 20 missions sent to its surface, some more successful than others, have allowed scientists to learn surprising details about its orography. And the information doesn’t stop there.

Polygonal structures. One example is the polygonal structures discovered by the Zhurong rover, sent by the Chinese Academy of Space Technology (CAST) as part of the Tianwen-1 mission. As the paper published in the journal Nature describes, the rover’s instruments detected these structures at a depth of about 115 feet as it traversed the Utopia Planitia region (the “plain of nowhere”).

These 16 formations extend over a distance of about 0.75 miles. The fact that Zhurong traversed less than a mile of the plain (just over 2,000 miles in diameter) leads scientists to believe that these structures occupy much of the region.

The structures found vary in size from a few inches to several feet. Their origin is still a mystery.

The causes. The team points to two possible explanations for the formation of the structures, one more likely than the other. One possibility is that they result from the lava’s cooling process.

However, the central hypothesis is that continuous freezing and thawing cycles formed these polygonal structures. This process also occurs on Earth. During the warmer seasons, water seeps into the irregularities of the rock. When the winter cold arrives, the water freezes.

In addition, ice is more voluminous than water, so it exerts pressure on the rock. Continuous cycles of freezing and thawing widen the cracks in these rocks, producing structures like those found in the Martian subsurface.

Stations on Mars. The team responsible for the discovery estimates that these rocky polygons formed about 3 billion years ago, between the late Hesperian and early Amazonian periods. During this time, Mars may have had a more oblique axis of rotation, which would have resulted in more pronounced seasons at mid and low latitudes. Thus, freeze-thaw cycles would have given way to these polygonal formations.

Zhurong. The ground-penetrating radar aboard the Chinese Zhurong rover made the detection of the structures possible. The rover landed on Mars with the Tianwen-1 mission on July 23, 2020, and began its journey away from the lander on May 14, 2021.

The rover remained active until May 2022, when scientists from CAST put it into hibernation mode in anticipation of the Martian winter and the arrival of sandstorms. The rover didn’t resume activity, probably due to the accumulation of sand on its instruments.

Image | China News Service | NASA/JPL/University of Arizona

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