spaceSpace and PhysicsspaceAstronomy

Weird Buried Polygonal Structures Found On Mars By Chinese Rover

The now-defunct Zhurong used radar to find what lies beneath Utopia Planitia.


Dr. Alfredo Carpineti


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

Alfredo (he/him) has a PhD in Astrophysics on galaxy evolution and a Master's in Quantum Fields and Fundamental Forces.

Senior Staff Writer & Space Correspondent

the photo shows zhurong on the surface of mars. To its left the lander is visible

Zhurong and its lander taking a selfie.

Image credit: China News Service via Wikimedia Commons (CC BY 3.0)

Chinese rover Zhurong was the first Chinese mission to land on Mars, exploring one of the Red Planet’s largest impact basins: Utopia Planitia. This area was visited by Viking 2 in 1976 and decades of technological advancement meant that Zhurong could deliver new insights on the region. And some of them came from below the surface of the planet. The rover found 16 polygonal structures buried beneath the surface.

Researchers believe that these were formed in the context of freeze-thaw cycles that led to the formation of cracks in the terrain, which was originally on the surface. As seen in other terrains on Mars, sublimation and freezing can carve the terrain in peculiar ways (such as the so-called spiders) and it seems to be that this process is nothing new on Mars. It might have been going on for billions of years.


The work from Zhurong’s radar shows that some of this cracked terrain and its polygonal structure can get buried. The formation was underneath 35 meters (115 feet) of ground. Previous work focused on the vertical layers of the region. This indicated that there have been several episodic floods that filled the basin, roughly around 3 billion years ago. The new work uncovered instead what the layers are like horizontally by looking at the radar analysis across the 1.9 kilometers (1.2 miles).

Four images show the process. First moisture moves through the ground. In the second ice creates a wedge. In the third sublimation creates cracked terrain. And in the fourth the cracked terrain is buried.
Formation scenario for the polygonal structure buried under Utopia Planitia.
Image credit: Zhang et al, Nature Astronomy 2023 (CC BY 4.0)

Mars used to be a volcanic world: the tallest volcano in the Solar System is on Mars. Some geological activity persists to this day, with marsquakes recorded on the Red Planet by NASA’s InSight. 

So, the researchers considered the possibility that the buried structure had a lava origin. On Earth, there are several examples of these, such as the Giant's Causeway. However, there was no evidence of basaltic extrusions where Zhurong had explored. The team is confident that the structures are sedimentary, formed from thermal processes in varying climates.

And that’s an intriguing consequence of this study. If the polygonal structures required freezing-and-thawing events, the climate of ancient Mars ought to have been a lot more variable. Utopia Planitia is at low-to-mid latitudes. The area is 25 degrees north of the Martian equator. But the planet might have had had a higher obliquity, so the region might have experienced wildly different seasons.


The layers indicate more has happened in the past. The polygonal structures were buried in layers of material that look nothing like them. Maybe the wet environment that formed them stopped existing, or some other unknown geological event took place.  

“Occurring at low latitudes (∼25° N), the polygonal terrain, which is interpreted as having most likely formed by thermal contraction cracking, makes a compelling case for the high obliquity of early Mars. The subsurface structure with the covering materials overlying the buried palaeo-polygonal terrain suggests that there was a notable palaeoclimatic transformation some time thereafter,” the authors wrote.

The study is published in Nature Astronomy.

[H/T: Universe Today]


spaceSpace and PhysicsspaceAstronomy
  • tag
  • geology,

  • Mars,

  • Astronomy,

  • Red Planet,

  • Mars rover,

  • Zhurong