X-ray data from NASA's MESSENGER probe points to high levels of magnesium and sulfur on the surface of the planet Mercury, suggesting its makeup is far different from that of other planets, scientists say. The unmanned orbiter has been beaming back data from the first planet for a year and a half. Readings from its X-ray spectrometer point to a planet whose northern volcanic plains formed through upwellings of rocks more exotic than those often found on the Earth, the Moon or Mars, said Shoshana Weider, a researcher at the Carnegie Institution of Washington.