An astronaut had a chilling surprise when they spotted a huge skull on Earth.

An unnamed crew member of the International Space Station (ISS) snapped the eerie sight earlier this year.

NASA have now released the image, which they have entitled “A Ghostly Face in the Rock”.

It shows a huge volcanic pit in northern Chad, with the skull illusion caused by shadows and volcanic features.

The space agency explain: “From above, the 1,000-metre (3,300-foot) deep volcanic pit and soda lake Trou au Natron in northern Chad has the look of a ghostly face staring back at you.

“An astronaut on the International Space Station captured this photograph of the distinctive feature on February 12, 2023.

“The edge of the “face” is partly formed by shadows cast by the rim of a caldera—a type of volcanic crater formed after an explosive eruption or the collapse of the surface into a partially-emptied magma chamber.

“The “eyes” and “nose” are cinder cones—steep conical hills built around volcanic vents. The cinder cones are thought to be relatively young in geological terms, likely forming within the past few million years and possibly as recently as the past few thousand years.

“The white area around the “mouth” is a mineral crust made of a salt known as natron—a mixture of sodium carbonate, sodium bicarbonate, sodium chloride, and sodium sulfate. It forms as hot spring water pools on the surface and evaporates, and mineral-rich steam rises from the surface of the geothermally active area.”

Trou au Natron lies just southeast of Tarso Toussidé, a broad volcanic feature with fumaroles and an active stratovolcano. One of several volcanic peaks in the Tibesti Mountains, it is the source of several relatively recent—though poorly documented and studied—eruptions.

The remoteness of Trou au Natron makes it difficult for scientists to access. However, analysis of rock and fossil samples collected in the 1960s indicate that Trou au Natron was filled by a glacial lake hundreds of meters deep about 14,000 years ago.

An expedition led by German researcher Stefan Kröpelin reached Trou au Natron in 2015 and collected samples of fossilised aquatic algae thought to have formed some 120,000 years ago.

NASA say satellite observations of the region have helped fill in some details.

They explain: “One pair of University of Cambridge researchers have pieced together a rough sequence of the region’s volcanic activity based on observations from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor on NASA’s Terra satellite. They divided the activity into six phases, with the formation of Trou au Natron as one of the most recent events of geologic significance.”

The astronaut photograph was acquired on February 12, 2023, with a Nikon D5 digital camera using a focal length of 500 millimeters. It was taken by a member of the Expedition 68 crew.

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