Mercury is a desert world which scientists until recently considered quite uninteresting. NASA’s Mariner and MESSENGER missions, however, revealed that there is much more to the smallest and innermost planet of the Solar System than meets the eye. Despite temperatures on its surface rising up to 450°C, there seems to be water ice on Mercury. The planet also appears to have a way too large inner core for its size and a surprising chemical composition. Here are the top five Mercury mysteries that the European-Japanese BepiColombo mission might solve.