title: Early lunar magnetism.
abstract: It is uncertain whether the Moon ever formed a metallic core or generated a core dynamo. The lunar crust and returned samples are magnetized, but the source of this magnetization could be meteoroid impacts rather than a dynamo. Here, we report magnetic measurements and 40Ar/39Ar thermochronological calculations for the oldest known unshocked lunar rock, troctolite 76535. These data imply that there was a long-lived field on the Moon of at least 1 microtesla approximately 4.2 billion years ago. The early age, substantial intensity, and long lifetime of this field support the hypothesis of an ancient lunar core dynamo.
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 54-521, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. iang@mit.edu
authors.forename: Ian
authors.initials: I
authors.lastname: Garrick-Bethell
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Weiss
authors.forename: David L
authors.initials: DL
authors.lastname: Shuster
authors.forename: Jennifer
authors.initials: J
authors.lastname: Buz