WHAT looks like a grisly, sun-scorched human face has been found half-buried in the sand on Mars by Nasa's Perseverance rover.
An image taken by the rover in September appears to show a sandy face with a large brow bone, nostrils and a sloping mouth.
Although it may look like the remains of a decapitated head, it is actually a rock.
Experts believe the formation is just another hunk of sedimentary sandstone, a leftover from the planet's water-rich past.
Its unusual shape suggests it was affected by water erosion when rivers used to flow on the Martian surface roughly 3.8billion years ago.
The rock has triggered a psychological phenomenon called face pareidolia.
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This is the tendency to see human facial features in inanimate, or lifeless objects.
In 1976 the same phenomena birthed the famous 'Face on Mars' image taken by the American Viking 1 Orbiter.
At the time, Nasa released a statement saying one of several Martian formations in the Cydonia region "resembles a human head".
It was merely an optical illusion caused by the way sunlight hit the formations, resulting in shadows that gave impressions of eyes and a mouth.
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'Zebra rock'
Nasa has been exploring Mars from afar for decades.
The Red Planet is blanketed with sand, rocks, ice, dust, clouds, craters and holes.
Every so often, bizarre discoveries like a mysterious "doorway" or "spaghetti monster" will take the internet by storm - before being quickly debunked by experts.
Yet, one recent rocky discovery has caused intrigue, with the US space agency stating it is "unlike any" debris seen on Mars before.
The object of this fascination is a black and white striped rock, dubbed 'Freya Castle' or "zebra rock".
The loose stone was found in the Jezero Crater, where scientists believe they have the best chance of finding remnants of ancient alien life.
Perseverance, which has been roaming Mars since July 2020, found the rock on a flat sandy plane above the deep sloping sides of the 1,000metre-deep crater in August.
The Jezero Crater is thought to be what's left of an ancient lake.
"While driving across unremarkable pebbly terrain, beady-eyed team members spotted a cobble in the distance with hints of an unusual texture in low resolution Navcam images, and gave it the name ‘Freya Castle’," Nasa wrote in a statement.
The team planned a multispectral observation, a picture that shows beyond what the human eye can see, including infrared and ultraviolet light, using the Mastcam-Z camera.
"When these data were downlinked a couple days later, after Perseverance had already left the area, it became clear just how unusual it was," Nasa added.
"The internet immediately lit up with speculation about what this 'zebra rock' might be, and we’ve enjoyed reading your theories!"
The stone, about 20cm in size, is unlikely to have originated from the area in which it was found, with experts suggesting it could have rolled downhill from a source higher up.
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"This possibility has us excited, and we hope that as we continue to drive uphill, Perseverance will encounter an outcrop of this new rock type so that more detailed measurements can be acquired," the team concluded.
"Could these be our first glimpses at ancient rocks uplifted from depth by the Jezero impact, now exposed on the crater rim? Only time will tell…"
Mars facts
Here's what you need to know about the red planet...
- Mars is the fourth planet from the Sun
- It is named after the Roman god of war
- The landmass of Mars is very similar to Earth but due to the difference in gravity you could jump three times higher there than you can here
- Mars is mountainous and hosts the tallest mountain known in the Solar System called Olympus Mons, which is three times higher than Everest
- Mars is considered to be the second most habitable planet after Earth
- It takes the planet 687 Earth days to orbit the Sun
- The planet has a diameter of 4,212 miles, and has an average distance from Earth of 140 million miles
- Martian temperatures can vary wildly, reaching as high as 70F/20C or as low as -225F/-153C