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Summary
Tiny and relatively ignored, Mercury holds outsize mysteries. Only two spacecraft have made the difficult journey to its sun-baked environs. NASA's Mariner 10 flew by the planet in the 1970s but getting a spacecraft into orbit around Mercury without it plummeting into the sun proved tricky. It wasn't until the 1980s that mission planners worked out the complex series of gravity assists needed and longer still to design spacecraft able to endure the sun's heat. The next visitor, NASA's MESSENGER, finally arrived in 2011 and promptly upset many theories about the planet's formation and evolution through observations of Mercury's skewed magnetic field, its outsize iron core, and strange lakelike depressions perhaps carved by escaping volatile elements. Researchers now hope to get answers from the planet's third and most ambitious visitor, the European-Japanese mission BepiColombo, a pair of probes due for launch on 20 October.
