The European Space Agency's Mars Express has captured a unique crater on Mars similar to the eye of Sahara, which is 30 kilometers wide.

The eye of Sahara, a geological formation that was first photographed by Gemini astronauts in the 1960s, has been a mysterious phenomenon for decades.

A similar structure has now been seen on Mars, where a 30 km-wide unnamed crater has been seen in the Aonia Terra region.

The image captured by the European Space Agency's Mars Express shows part of Aonia Terra, an upland region in the southern highlands of the Red Planet.

The crater is in the center of a landscape of winding channels that appear like veins running through a human eyeball.

Astronomers suspect that the channels are likely to have carried liquid water across the surface of Mars around 3.54 billion years ago.

According to ESA, the channels look as if they are partly filled with a dark material, and in some places, seem to actually be raised above the surrounding land.

" There are a variety of possible explanations for this. Perhaps erosion-resistant sediment settled at the bottom of the channels when water flowed through them.

Or perhaps the channels were filled in with lava later on in Mars’ history," ESA said in a statement released with the image.