spacetoday.net: Mercury has molten core

Posted: Sat, May 5, 2007, 10:03 AM ET (1403 GMT)
Mercury spin illustration (NRAO)

Scientists have determined that the core of innermost planet Mercury is most likely molten, a discovery that may explain why the planet is able to sustain a magnetic field. In a paper published in this week's issue of the journal Science, researchers used radio telescopes in West Virginia and Puerto Rico, as well as a NASA Deep Space Network antenna in California, to bounce radio waves off of Mercury. The observations allowed scientists to measure minute variations in the planet's rotation rate, which are best explained if the planet's core is molten rather than solid. Scientists had known that Mercury had a weak magnetic field, about one percent as strong as the Earth's, since the Mariner 10 spacecraft flew past the planet over three decades ago; such magnetic fields are usually generated by an electromagnetic dynamo that requires a molten core, but the planet has previously been believed to be too small to sustain a molten core.