New focus on Mercury

The first round of data pouring in from NASA’s spacecraft may invalidate hypotheses about the formation of Mercury, the dry and blistering planet closest to the sun. The early results also add to evidence that water ice may exist on the planet, scientists said at a June 16 press conference. Messenger (MErcury Surface, Space ENvironment, GEochemistry & Ranging) data show that Mercury’s surface contains not only high levels of sulfur but also a high potassium-to-thorium ratio. Because potassium evaporates at much lower temperatures than thorium, the ratio of the two elements is often used to probe thermal processes in the early solar system. Scientists expected that the sun would have long ago blasted potassium from Mercury. The high levels discovered by Messenger rule out models predicting that Mercury formed, like Earth, from accreting matter from the solar system disc or from a metal-rich meteorite, researchers say. Messenger’s scans of Mercury’s north pole also confirmed that a number of craters there are permanently shadowed. These craters coincide with bright spots that ground telescopes detected in the 1990s and were hypothesized to be water ice. Now, their coincidence with the permanently shadowed craters strengthens the case for that 20-year-old hypothesis.