Magnetic mission Artist’s impression of NASA’s MESSENGER spacecraft orbiting Mercury. (Courtesy: JPL/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)"> Magnetic mission Artist’s impression of NASA’s MESSENGER spacecraft orbiting Mercury. (Courtesy: JPL/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

A new study using data from a space mission suggests that most of Mercury’s crustal magnetic fields can be explained by iron and other magnetized rocks in the crust responding to the planet’s weak present-day core magnetic field, rather than from an ancient field, as had been inferred previously. Mercury is the only solar-system planet other than Earth to possess both a global magnetic field arising from its core and a crustal magnetic field resulting from rocks that were magnetized in either the present-day or an ancient core field.…