Mysterious landmarks on Mars have been discovered by NASA

NASA has shared images of bizarre looking landmarks on Mars over the years — prompting many to debate the possibility that the Red Planet was once home to aliens.

Our fascination with Mars is one which simply refuses to die.

As one of Earth's closest neighbours and one of the more likely candidates for life - let's be honest, nobody is surviving on the gassy giants such as Jupiter and Saturn - the Red Planet remains one of the focal points in our search for a lost alien civilisation.

Often living up to its nickname, Mars often looks like a desolate red wasteland in images shared by NASA. However this hasn't stopped online sleuths from pouring over satellite imagery in hopes of finding signs of life.

And of course, anyone who looks long enough is bound to find something.

One particular image which has captured the attention of alien sleuths is the image of an 'exclamation mark' landmark on the planet.

Captured in 2011 by NASA's Mars Reconnaissance Orbiter (MRO), the spacecraft was able to capture the image of what appeared to be a giant exclamation mark on the Libya Montes highland area of the Mars.

Could this be finally be evidence of the long lost alien civilisation we've all been looking for? As always, it depends on who you ask.

What do you think, man-made or naturally occurring? (NASA/JPL-Caltech/UArizona)

'No way to explain' the formation on Mars

One supporter of this theory is George J. Haas, founder of Mars research group The Cydonia Institute, who recently told MailOnline: "You don't have to be a geologist to know the difference between a rock and a sculpture."

"There's no way you can explain that keyhole formation," he continued, adding: "The natural creation of two opposing geometrically designed formations seems to go well beyond the probability of chance."

The 'exclamation mark' isn't the only landmark which Haas has flagged as suspicious over the years either, with the author highlighting images such as pyramid-like structures which were captured by astronomer Carl Sagan in 1972 as well as geometric patterns which resemble ancient cities and the infamous 'face' in the planet's Cydonia region.

The cydonia region of Mars, which attracted attention after one of the mountains resembled a face (Photo12/Universal Images Group via Getty Images)

Evidence of alien civilisation or examples of the pareidolia effect?

However, not everyone would agree, with many scientists arguing that it is all down to a phenomena known as the 'pareidolia effect'.

A blog post from The Planetary Society has since branded the image as one of the many examples of 'pareidolia', which is the phenomenon in which humans are able to perceive shapes and patterns in completely random images.

Common examples of pareidolia include seeing faces in inanimate objects such as clouds, the face of Jesus in the Shroud of Turin, underwater 'pyramids' or 'structures' on Mars.