Planetary astronomers say that some theories about the origin of Mercury need to be discarded, based on data from NASA's Mercury MESSENGER probe that settled into orbit around the barren planet in 2011.
MESSENGER - an acronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging - revealed that Mercury is so chemically diverse that it could not have formed simply as a hot ball of molten iron as shown in most textbooks, researchers conclude. What's more, the planet is much more geologically diverse than our moon, which was once considered Mercury's cousin.
MESSENGER has also confirmed that unusual radar-bright deposits of something - perhaps water - are hidden in permanently shadowed areas at the planet's poles.
Mercury is "wonderfully dynamic" says Sean Solomon of the Carnegie Institution of Washington.
Here are some of the top discoveries as reported by Solomon at the recent meeting of the American Astronomical Society in Anchorage, Alaska: