And a new set of pictures released by NASA could appear to confirm conspiracy theorists' claims that we are not alone in the universe.
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The images taken by a NASA navigation camera have been released and appear to show a human-like figure working on the Mars Curiosity Rover, which is scanning the Red Planet.
The pictures have been reported to the monitoring website UFO sightings daily, and have sent conspiracy theorists into overdrive, with some claiming it is proof life does exist on Mars.
It comes after Gary McKinnon, an alleged computer hacker, who reportedly obtained classified documents from the U.S. government, claimed he found files showing the existence of 'extra-terrestrial officers'.
However, others have claimed that the Curiosity Rover might not even be on Mars and that it has remained on Earth with humans cleaning it and performing maintenance.
But some insist the shadow is just coincidence and that conspiracy theorists are only seeing the figure because it confirms their expectations and hopes.
Nigel Watson, author of the UFO Investigations Manual, said: 'This underlines the fact that such things literally lurk in the shadows and play with our imagination.'
It comes after it was announced in December that an instrument on the Curiosity Rover had identified spikes of methane that scientists believe may have come from bacteria-like organisms on the surface of Mars.
The new discovery, reported in the journal Science, followed studies of gas samples by Curiosity's Tunable Laser Spectrometer (TLS) - an instrument that uses intense light to carry out chemical analysis.
It revealed a low background level of methane, which spiked 10-fold over a period of just 60 Martian days.
While there are non-biological explanations, experts suggested that its finding may be a sign of life on Mars.
The Mars Curiosity Rover, is a probe designed to help with long-term exploration of the Red Planet.
Its aim is to assess whether the planet has ever had an environment, which has been able to support small life forms and to determine whether the planet could be habitable.