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.