Shark on Mars
A fish-shaped rock at the bottom of the image released by Nasa has UFO theorists speculating on life on the planet Nasa

Any picture of Mars by Nasa's Curiosity rover catches the attention of UFO theorists. Quick to 'spot' fossils on the barren and rocky land of the red planet, they are then offered as theoretical proof that life existed on the planet. Now, a rough photograph, shared by Nasa, reveals a rock imprint which has an eerie resemblance to a large fish.

The image has again sparked life-on-Mars speculations among UFO theorists who are linking it to an earlier statement by Nasa claiming the planet once had water. "Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space," Geronimo Villanueva, a scientist at Nasa's Goddard Space Flight Center in Greenbelt, Maryland had said in 2015. "With this work, we can better understand the history of water on Mars."

Commenting on the fish-shaped rock in the image, Scott C Waring, of the website UFO Sighting Daily, wrote: "Last year Nasa announced that there were oceans on Mars and that it did look a lot like Earth in many ways. I guess this petrified fish is a proof of that. Look closely and you will see the tail fin and the fin ridge that starts at the lower back fin and moves all the way to the fish's stomach. I coloured the fish to make it easier on the eyes. The fish is also about half a meter long, about the size of a bass or a small salmon."

This is not the first time UFO hunters have been coming up with bizarre theories of life in outer space. They have also reported on sightings of shapes that resemble giant crabs, coffins and gorillas, besides pyramid-like formations to further their theory that the planet harbours intelligent life. Until now, however, none of the pictures from Curiosity's mission has nudged at the existence of extra-terrestrial life on Mars or elsewhere.