Scientists have argued about the origins of Mercury’s smooth plains and the source of its magnetic field for over 30 years. Now, analyses of data from the January 2008 flyby of the planet by the MESSENGER spacecraft have shown that volcanoes were involved in plains formation and suggest that its magnetic field is actively produced in the planet’s core and is not a frozen relic. Scientists additionally took their first look at the chemical composition the planet’s surface material. The tiny craft probed the composition of Mercury’s thin atmosphere, sampled charged particles (ions) near the planet, and demonstrated new links between both sets of observations and materials on Mercury’s surface. The results are reported in a series of 11 papers published in a special section of the July 4 issue of Science magazine. [more]