This spiral-shaped geological formation, also known as "the Eye of the Sahara", is about 50 kilometers in diameter.

Photo: Twitter @Astro_Wakata.

Japanese astronaut Koichi Wakata shared images of the Richat Structure taken from the International Space Station (ISS) on social media.

This spiral-shaped geological formation, also known as "the Eye of the Sahara", is about 50 kilometers in diameter and is located in Mauritania, in the western region of that African desert.

"It is clearly visible from the ISS!" Wakata highlighted in his message.

The Eye of the Sahara looks straight into outer space, but how did this gigantic geological structure form?

Here we explain:

With an approximate diameter of 50,000 meters, geographers and astronomers agree that it is a 'curious' geological formation.

Some scientists think that it was formed after the collision of a gigantic asteroid.

Others, however, believe that it has to do with a dome that eroded with the force of the wind.

Located northwest of Mauritania, at the western end of Africa, what is truly incredible is that it has concentric circles inside.

This is what is known, so far, about this anomaly on the earth's crust.

How was the Eye of the Sahara formed?

Rumor has it that the circumference of the Eye of the Sahara marks the trace of an ancient lost city.

Others faithful to conspiracy theories claim that it was part of a monumental alien structure.

In the absence of conclusive evidence, all these hypotheses have been relegated to the realm of pseudoscientific speculation.

In fact, the official name of this landform is

.

Its existence has been recorded since the 1960s, when NASA Gemini expedition astronauts used it as a reference point.

Back then, it was still thought to have been the product of a colossal asteroid impact.

Aerial view showing the 'porthole' of the Richat Structure, also known as 'Guelb er Richat', an eroded geological dome, exposing layered sedimentary rocks resembling concentric rings, on the Adrar Plateau of the Sahara, in the Northwest Africa, as seen from the Space Shuttle Columbia during the STS-58 mission, October 30, 1993.|

Credit: Space Frontiers/File Photos/Hulton Archive/Getty Images.

Currently, however, we have other data:

"It is believed that the circular geological feature is caused by a raised dome (geologists would classify it as a vaulted anticline) that has eroded to expose originally flat rock layers," documents the same space agency.

Sedimentary sampling of the area indicates that it was formed approximately 542 million years ago.

This would place it in the late Proterozoic, documents IFL Science, when a process known as folding occurred, in which "tectonic forces [...] squeeze the sedimentary rock."

This is how a 'symmetrical anticline' was formed, which gives it the shape of a circle.

Where do the colors of the structure come from?

Colorful collage of the Richat structure, made by NASA.

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Credit: NASA/Getty Images

The Eye of the Sahara has been widely studied from different branches of science.

In fact, a study published in 2014 for the Journal of African Earth Sciences ensures that the Richat Structure was not a product of plate tectonics.

Rather,

Before being eroded, the scientists explain, the rings that can be seen on the surface today were formed.

Due to the antiquity of the circle, it could have been the product of the separation of Pangea: the supercontinent that gave rise to the distribution that the Earth has today.

Regarding the colorful patterns that can be seen on the surface of the structure, the researchers agree that it has to do with the types of rock that have emerged through erosion.

Among them, fine-grained rhyolite and coarse crystalline gabbro rocks that have undergone hydrothermal alteration have stood out.

Hence the Eye of the Sahara does not have a uniform 'iris'.

Image taken during Expedition 59 of the International Space Station (ISS) |

Credit: NASA/Mark Garcia

(With information from RT and National Geographic in Spanish)