A huge door-like object has been spotted on the planet Mercury's surface and UFO hunters are convinced it is a portal for alien spacecraft to travel in and out. The bizarre image - captured on the Victoria Rupes Cliffs on the Solar System's smallest planet - appears to show a rectangular shape sitting next to a crater. And alien fanatic Scott C. Waring - who first discovered the shape - is certain the object is proof of an alien doorway. "I was looking over some Mercury photos and found this unusual black doorway," he said. "It is long and rectangle in shape with four almost perfect right-angled corners. "Unless meteor cubes are pummelling planets, this seems to be made by ancient aliens." Scott went on to explain how the "doorway" measured 3.4 miles long. He added: "That is a giant doorway for giant ships to travel through." The images first circulated a couple of years ago on Scott's blog ufosightingsdaily.com, but were picked up yesterday (November 8) by conspiracy theorists