China discovers strange hexagonal structures on Mars

China’s Zhurong rover, which landed on Mars in 2021, continues to scan Utopia Planitia, one of the Red Planet's largest impact basins. This region was visited by Viking 2 in 1976, and decades of technological advancement meant that Zhurong could provide new information about the area. Some of this new information came from beneath the planet's surface. The rover found 16 polygonal structures buried under the surface.

Researchers believe these structures formed in the context of freeze-thaw cycles that caused cracks to form in the terrain, which was initially on the surface. As seen in other regions on Mars, sublimation and freezing can carve the terrain into strange shapes, and it appears this process is nothing new on Mars and may have been ongoing for billions of years.

Data obtained from Zhurong’s radar shows that some of this cracked terrain and the polygonal structure could be buried. The formation was located 35 meters below the ground. Previous work had focused on the vertical layers of the region. This data indicated that several intermittent floods occurred that filled the basin approximately 3 billion years ago. The new study revealed how the layers are oriented horizontally by looking at radar analysis over 1.9 kilometers.

Mars was once a volcanic planet, and the tallest volcano in the Solar System is even on Mars. Some geological events, such as the Marsquakes 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 volcanic origin. Several different examples of this type, such as the Giant's Causeway on Earth, can be seen. However, since there was no evidence of basaltic outcrops where Zhurong made its discovery, the team is quite certain that the structures are sedimentary, formed by thermal processes in changing climates.

This may be the most intriguing result of this study. If the polygonal structures require freeze-thaw events, the climate of ancient Mars would have had to be much more variable. Utopia Planitia is located at 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 indicate that more events occurred in the past. The polygonal structures were buried in layers of material that did not resemble them at all. Therefore, it is possible that the wet environment that formed them disappeared or that another unknown geological event took place.

The study was published in Nature Astronomy.