Mercury’s magnetic field may be ancient

New Scientist : According to new data from NASA’s MESSENGER spacecraft, Mercury’s magnetic field could be as old as 3.7 billion to 3.9 billion years, almost as old as the planet itself. Although it was already known that Mercury had a bipolar magnetic field similar to that of Earth’s, its age could not be established until recently, when MESSENGER began to orbit closer to the planet preparatory to crashing into its surface. As MESSENGER‘s altitude decreased from 150 km to 15 km, the craft was able to detect a weak magnetic signal coming from rocks on Mercury’s surface, according to researchers, whose paper was published yesterday in Science. From the rocks’ heavily pockmarked condition, the researchers estimate their age at almost 4 billion years. If so, it’s possible Mercury has maintained a magnetic field for almost its entire existence. More may be learned from the next Mercury mission, the Japanese–European satellite BepiColombo, scheduled to launch in 2017.