Mystery of the alien plughole on Mars - strange terraced crater caused by gigantic slab of water ice An 'alien plughole' on Mars that has baffled scientists could have a simple explanation.
Astronomers claim the strange crater, which has a terraced rather than bowl pattern, has been created by water ice. To confirm their theory, researchers found an enormous slab of water ice just beneath the crater, measuring 130ft (40 metre) thick. The slab, which covers an area equivalent to that of California and Texas combined, was spotted by Nasa's Mars Reconnaissance Orbiter, or MRO. 'Craters should be bowl shaped, but this one had terraces in the wall,' says Ali Bramson, a graduate student in the University of Arizona's Lunar and Planetary Laboratory. Terraces can form when there are layers of different materials in the planet's subsurface, such as dirt, ice or rock. 'When the crater is forming, the shock wave from an object hitting a planet's surface propagates differently depending on what substrates are beneath the area of impact,' Bramson says. 'If you have a weaker material in one layer, the shock wave can push out that material more easily, and the result is terracing at the interface between the weaker and stronger materials.'
