Mars is surely the planet (apart from our own, of course) that attracts the most attention. The more than 20 missions sent to the surface of the neighbouring planet, some more successful than others, have allowed us to learn surprising details about its topography. And the stream of information continues.
Polygonal structures. An example of this are polygonal structures. discovered by the rover Zhurongthe vehicle sent by the Chinese Academy of Space Technology as part of the Tianwen-1 mission. The instruments on the rover They detected these structures at a depth of about 35 meters as they traveled through the region called Utopia Planitia (the “plain of nowhere”).
These formations, 16 in total, are spread over a stretch of about 1.2 kilometers in length. The fact that Zhurong had traveled only two kilometers of the plain (which itself has a diameter of just over 3 km) suggests that these structures extend over a large part of the region.
The structures found vary in size, from those measuring just a few centimetres to those reaching several metres. Their origin remains a mystery.
Explanations. The team points to two possible explanations for the formation of the structures, one more likely than the other. One possibility is that they are a consequence of the cooling process of the lava.
However, the main hypothesis is that These structures They were formed by continuous cycles of freezing and thawing. We also see this process on Earth: during the warmer seasons, water seeps into the irregularities of the rock, and when the winter cold arrives, the water freezes.
Ice is more voluminous than water, so it exerts pressure on the rock. Continuous cycles of freezing and thawing enlarge the fissures in these rocks, potentially generating structures like those detected in the Martian subsoil.
Seasons on Mars. The team responsible for the discovery estimates that these rock polygons were formed about 3 billion years ago, between the late Hesperian period and the early Amazonian. During this era, Mars may have had a more oblique axis of rotation, which would have resulted in more marked seasons at mid- and low latitudes, thus allowing for the freeze-thaw cycles that would have given rise to these formations.
The details of the study were published in an article in the magazine Nature.
Zhurong. Detecting the structures was possible thanks to ground penetrating radar or GPR (ground penetrating radar) aboard China’s Zhurong rover. The vehicle landed on Mars with the Tianwen-1 mission on July 23, 2020, and launched its journey away from the lander on May 14, 2021.
The rover remained active until May 2022, when it was put into hibernation mode to await the Martian winter and the arrival of sandstorms. The vehicle never resumed activity, probably due to the accumulation of sand on its instruments.
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Image | NASA/JPL/University of Arizona/Zhang, Li, et al., 2023 / China Academy of Space Technology
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