Scientists intrigued by Mars' 'mysterious' craters

There are many great mysteries on Mars. Was there ever microbiological life there? Under the polar cap, are there any undiscovered "lakes"? The Arabia Terra region in the northern half of Mars is home to a number of craters, which are surrounded by a number of intriguing mysteries.

Using its HiRise camera, NASA's Mars Reconnaissance Orbiter took several aerial photos of craters in Arabia Terra. 

According to Paul Geissler of the HiRise team, the craters in question "contain unusual deposits with puzzling forms and distribution." University of Arizona researchers manage HiRise, reported CNET.

The crater enigma is complicated in many ways. According to Geissler, the deposits feature horizontal laminations that could be strata or terraces. They also have ridges that radiate light. Only the south sides of craters larger than 1,970 feet (600 metres) in diameter have peculiar deposits. Smaller craters are devoid of them.

The unique shapes are quite puzzling, but there may be an explanation related to the sublimation of glacial material on Mars (sublimation is the process of a solid turning directly into a gas).

"The terraces might represent different epochs of sublimation," Geissler wrote. "Perhaps the larger craters penetrated to a water table between 45 and 60 metres below the surface and were flooded after formation."

Mars values sublimation a lot. The "Happy Face Crater," a crater located in the planet's icy south polar zone, is a great example. The crater's appearance, as well as the smiling face inside it, have evolved with sublimating frost over time.