A 'cannonball' on Mars has UFO hunters excited

Mars is apparently fully inhospitable now but based on certain images, some think it was quite different in the past.

One alien hunter says the 'cannonball' is evidence of a war that ultimately ended life on Mars.

However, NASA says the ball is a rock that has turned round following a natural process. Find out more in the video above.

See also: UFO spotted in sky moments before motorway crash

See also: Is this evidence of an alien civilisation on Mars?