National Aeronautics and Space Administration scientists have argued about the origins of Mercury's smooth plains and the source of its magnetic field for more than 30 years. Those mysteries have now been solved by data from the January flyby of the planet by the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft called Messenger.

NASA scientists said they also studied the chemical composition of Mercury's surface, analyzed the composition of the planet's thin atmosphere, sampled charged particles (ions) captured near the planet and demonstrated new links between both sets of observations and materials on Mercury's surface.

The scientists also determined Mercury's core makes up at least 60 percent of its mass -- a figure twice as large as any other known terrestrial planet.

The results of the study of data produced by Messenger, led by Sean Solomon of the Carnegie Institute, are reported in a series of 11 papers published in a special section of Science magazine.