Science: An analysis of the magnetic fields recorded in a meteorite that originated on Vesta may prove that the asteroid once had a molten core. By progressively demagnetizing samples from the meteorite, a team led by MIT’s Roger Fu was able to identify a weak magnetic field dating to about 3.7 billion years ago. However, that is approximately 1 billion years after Vesta’s core stopped rotating and generating a magnetic field. As Vesta cooled, the rotating core would have imprinted a magnetic field into the crystals that formed in the asteroid’s crust. Fu’s team believes that an impact by another asteroid melted the area of the crust where the meteorite originated from, erasing the original magnetic field imprint. The field that the team detected would have been imprinted by the magnetic fields in the nearby areas of the crust that were not melted by the asteroid collision. An impact from yet another asteroid would have ejected debris, of which the meteorite that Fu examined was part.