China’s Mars rover Zhurong was the first Chinese mission to land on Mars to explore Utopia Planitia, one of the Red Planet’s largest impact basins. This area was visited by Viking 2 in 1976, and decades of technological advancement meant that Zhurong could offer new information about the region. Some of this new information came from beneath the planet’s surface. The rover found 16 polygonal structures buried beneath the surface.
Researchers believe these structures formed in the context of freeze-thaw cycles that caused cracks to form in the originally surface terrain. As has been seen in other regions on Mars, sublimation and freezing can carve the landscape in strange ways, and it appears that this process is nothing new on Mars and may have been going on for billions of years.
Data from Zhurong’s radar shows that some of this cracked terrain and its polygonal structure may be buried. The formation was located 35 meters underground. Previous work focused on the vertical layers of the region. These data showed that several intermittent floods occurred that filled the basin about 3 billion years ago. The new study looked at radar analysis across 1.9 kilometers to reveal how the layers lay horizontally.
Mars used to be a volcanic planet, and even the highest volcano in the Solar System was on Mars. Some geological events, such as Mars quakes recorded on the Red Planet by NASA’s InSight, continue to this day.
For this reason, researchers considered the possibility that the buried structure was of lava origin. Several different examples of this kind can be seen on Earth, such as the Giant’s Causeway. But since no evidence of basaltic outcrops was found where Zhurong discovered, the team is fairly confident that the structures are sedimentary, formed from thermal processes in changing climates.
This may be the most interesting result of this study. If polygonal structures required freeze-thaw events, the climate of ancient Mars would have been much more variable. Utopia Planitia is located in low-to-mid latitudes, 25 degrees north of the Martian equator. However, the planet’s tilt could have been higher, so the region may have experienced very different seasons.
The layers show that more events occurred in the past. The polygonal structures were buried in layers of materials that looked nothing like them. Therefore, it may be possible that the wet environment that created them has disappeared or another unknown geological event has occurred.
The study was published in Nature Astronomy.
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