
A mysterious circular rock formation on the surface of Mars has been captured by one of NASA's Orbiters.

The formation was photographed by the Curiosity Rover this week and has excited alien hunters who invited speculation over how it came to be online.

They suggested that the rocks were 'arranged', laid out by another form of life, or that it was part of a larger, buried structure which has never before been seen.

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NASA's Curiosity Rover has captured a mysterious circular formation on rocks on the surface of Mars

Alien hunters were excited by the images (above, after color enhancement) and suggested that the rocks had been 'arranged' or could even be evidence of a larger, buried structure

'Whatever we're seeing here, it's in a perfect circle and it's much different from the craters that we normally see on Mars and the moon and throughout the other planets in the solar system. This almost looks like these rocks were arranged in this circular formation.

'Either that or this could potentially be some sort of ruin. One thing's for sure, I've never seen anything quite like it on Mars. It just looks eerily out of place,' one space enthusiast said in a video posted by the YouTube channel SecureTeam10.

CURIOSITY ROVER Curiosity's top speed is 1.5 inches (3.8 cm) per second. It's the fourth rover to visit Mars, and took around seven minutes to land on the red planet. The rover is fitted with 17 cameras, and weighs about the same as a Mini Cooper at about 2,000lb (900kg). Scientists considered 60 different possible landing sites before deciding to set Curiosity down in Gale Crater. Advertisement

They compared it to another formation, discovered in 2015, which appeared to bear similarities to Stonehenge.

The 'discovery', which was spotted on the top of a raised mound, became known as Marshenge. Experts ruled it out as evidence of alien life, saying it was more likely the result of natural geological phenomenons that are also seen on earth.

Internet users weren't convinced that the newly-photographed rock circle proved extra-terrestrial existence either.

'It's most likely geological. different rock minerals can sometimes make circles like that. The outer circle is made of different mineral than surrounding area,' said one. In the past, eager enthusiasts have claimed to spot pyramids and tree stumps on the Red Planet.

The Curiosity Rover itself was photographed by another of NASA's gadgets earlier in the week as it trundled along the Red Planet's dusty surface.

A stunning new image shows a look at the rocky mountainside terrain of Mars’ Mount Sharp – and, appearing as a bright blue speck at the center, the Curiosity rover can be seen as it presses onward in its uphill mission.

The MRO spotted the car-sized rover on June 5, 2017, just two months ahead of Curiosity’s fifth anniversary of its landing near Mount Sharp.

Rocks and sand can be seen all around the rover, whose color has been enhanced to make it easier to spot.

In 2015, 'Marshenge' - another rock formation which alien hunters likened to Stonehenge - was discovered

In April this year, alien hunters believed the Curiosity had captured an ancient tree stump as it roamed the planet's surface

The view was captured using MRO’s High Resolution Imaging Science Experiment (HiRISE) camera – the most powerful telescope ever sent to the red planet.

‘When the image was taken, Curiosity was partway between its investigation of active sand dunes lower on Mount Sharp, and “Very Rubin Ridge,” a destination uphill where the rover team intends to examine outcrops where hematite has been identified from Mars orbit,’ according to NASA.

Since reaching Mars, the MRO has continually sent back remarkable observations to help scientists better understand the Martian surface - and, sometimes it presents new mysteries as well.

A stunning new image shows a look at the rocky mountainside terrain of Mars’ Mount Sharp – and, appearing as a bright blue speck at the center, the Curiosity rover can be seen as it presses onward in its uphill mission

The view was captured using MRO’s High Resolution Imaging Science Experiment (HiRISE) camera – the most powerful telescope ever sent to the red planet. ‘When the image was taken, Curiosity was partway between its investigation of active sand dunes lower on Mount Sharp,' according to NASA

A bizarre pit in Mars’ southern hemisphere, for example, has left scientists baffled as to how it formed.

The feature, which resembles the home of a fictional Star Wars beast that could swallow a person whole, may have been created from an impact with a rogue space rock – or, it could be the result of a collapse at the surface.

A stunning image captured by the HiRISE instrument on NASA’s Mars Reconnaissance Orbiter revealed a look at the strange circular formation and the surrounding ‘Swiss cheese terrain’ on the red planet.

The image was captured on March 25, during the late stages of summer in Mars’ southern hemisphere, researchers say.

At this time, the sun sits low in the sky, better revealing the subtle texture of the Martian surface.

A bizarre pit in Mars’ southern hemisphere has left scientists baffled as to how it formed. The feature, which resembles the home of a fictional Star Wars beast that could swallow a person whole, may have been created from an impact with a rogue space rock – or, it could be the result of a collapse at the surface

The stunning new image captured by the HiRISE instrument has revealed a look at the strange circular formation and the surrounding ‘Swiss cheese terrain’

‘We see many shallow pits in the bright residual cap of carbon dioxide ice (also called “Swiss cheese terrain”),’ wrote Alfred McEwen, of the University of Arizona’s Lunar & Planetary Laboratory.

‘There is also a deeper, circular formation that penetrates through the ice and dust.’

From the angle captured by HiRISE, the depression looks much like the Great Pit of Carkoon, which housed Jabba the Hutt’s carnivorous sarlacc in the Star Wars series (pictured)

The expert says the pit could be either an impact crater or a collapse pit, both of which are common on Mars.

From the angle captured by HiRISE, the menacing-looking depression looks much like the Great Pit of Carkoon, which housed Jabba the Hutt’s carnivorous sarlacc in the Star Wars series.

It isn't the first time scientists have spotted an unusual crater on Mars.

Earlier this year, researchers investigated a bizarre scaly feature discovered on the South Polar layered deposits.

While it’s thought to be an impact crater, the icy terrain experiences processes that drastically alter the form of surface features such as these, causing uncertainty about its true origin.

The size and frequency of impact craters on Mars can help scientist paint a clearer picture of a landscape’s age, according to NASA.

But, as they flatten and morph over time, it’s sometimes difficult to ascertain an impact origin.

This is the case with the strange scaly indent captured by the HiRISE instrument.

MARS: A WET PLANET Evidence of water on Mars dates back to the Mariner 9 mission, which arrived in 1971. It revealed clues of water erosion in river beds and canyons as well as weather fronts and fogs. Viking orbiters that followed caused a revolution in our ideas about water on Mars by showing how floods broke through dams and carved deep valleys. Mars is currently in the middle of an ice age, and before this study, scientists believed liquid water could not exist on its surface. In June 2013, Curiosity found powerful evidence that water good enough to drink once flowed on Mars. In September of the same year, the first scoop of soil analysed by Curiosity revealed that fine materials on the surface of the planet contain two per cent water by weight. Last month, scientists provided the best estimates for water on Mars, claiming it once had more liquid H2) than the Arctic Ocean - and the planet kept these oceans for more than 1.5 billion years. The findings suggest there was ample time and water for life on Mars to thrive, but over the last 3.7 billion years the red planet has lost 87 per cent of its water - leaving it barren and dry. Advertisement

An image of the feature projected at a scale of 50 centimeters (19.7 inches) per pixel shows how it dwarfs all the other pock-marks that dot the landscape.

It came just days after NASA revealed the Mars Reconnaissance Orbiter has completed 50,000 orbits around the red planet since 2006.

The space agency released a stunning animation that shows how the observations have accumulated over the last 11 years.

The mosaic shows the increasing coverage at just one frame per month, revealing how the orbiter’s Context Camera pieced together more than 99 percent of the Martian surface.

Scientists are investigating a bizarre scaly feature on the surface of Mars that could be the site of a past impact. The circular structure was discovered on the South Polar layered deposits, and a stunning new image from the Mars Reconnaissance Orbiter’s HiRISE instrument reveals a close look at its strangely reptilian appearance

As the craft completed its 50,000th orbit, the space agency has revealed a stunning new animation that shows how the observations have accumulated over the last 11 years. The mosaic shows the increasing coverage at just one frame per month

The orbiter’s Context Camera (CTX) ‘exploits a sweet spot in the balance between resolution and image file size,’ according to NASA.

It achieves a resolution of roughly 20 feet (6 meters) per pixel, and in the years since it switched on, it’s imaged 99.1 percent of Mars – about the equivalent of the land area of Earth.

According to the space agency, no other camera deployed to the red planet has captured such detailed observations as this.

Over about a decade, the camera has taken roughly 90,000 images, with each one covering a swath of ground roughly 18.6 miles wide.

Despite the distance, it can capture features as smaller than a tennis court.

The camera has made a few return trips, observing 60.4 percent of the planet more than once to help scientists better understand the surface, and learn more about future landing sites.

The orbiter’s Context Camera (CTX) ‘exploits a sweet spot in the balance between resolution and image file size,’ according to NASA. It achieves a resolution of roughly 20 feet (6 meters) per pixel, and in the years since it switched on, it’s imaged 99.1 percent of Mars – about the equivalent of the land area of Earth

‘Reaching 99.1 percent coverage has been tricky because a number of factors, including weather conditions, coordination with other instruments, downlink limitations, and orbital constraints, tend to limit where we can image and when,’ said Michael Malin, the Context Camera Team Leader, from Malin Space Science Systems, San Diego.

‘Single coverage provides a baseline we can use for comparison with future observations, as we look for changes.

‘Re-imaging areas serves two functions: looking for changes and acquiring stereoscopic views from which we can make topographic maps.’

The Context Camera has observed dramatic changes on the surface, including more than 200 observations of fresh impact craters, which have allowed scientists to calculate the rate of collisions from space rocks.

And, some of these craters have revealed material thought to be water ice.

The Mars Reconnaissance Orbiter was launched August 12,2005, and began capturing images after reaching orbit in 2006.

It eventually revised its orbit after several months, using the friction with Mars’ upper atmosphere.

Its latest adjustment took place earlier this year, using a 45.1-second burn of six intermediate-sized rocket engines to shift the orbit so the craft can be in the right place to receive transmissions from NASA’s InSight Mars lander, as it descends to the surface on Nov 26, 2018.

‘After 11 and a half years in flight, the spacecraft is healthy and remains fully functional,’ said MRO Project Manager Dan Johnston at NASA’s Jet Propulsion Laboratory.

‘It’s a marvellous vehicle that we expect will service the Mars Exploration Program and Mars science for many more years to come.’