title: The lunar dynamo.
abstract: The inductive generation of magnetic fields in fluid planetary interiors is known as the dynamo process. Although the Moon today has no global magnetic field, it has been known since the Apollo era that the lunar rocks and crust are magnetized. Until recently, it was unclear whether this magnetization was the product of a core dynamo or fields generated externally to the Moon. New laboratory and spacecraft measurements strongly indicate that much of this magnetization is the product of an ancient core dynamo. The dynamo field persisted from at least 4.25 to 3.56 billion years ago (Ga), with an intensity reaching that of the present Earth. The field then declined by at least an order of magnitude by ∼3.3 Ga. The mechanisms for sustaining such an intense and long-lived dynamo are uncertain but may include mechanical stirring by the mantle and core crystallization.
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. bpweiss@mit.edu.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Weiss
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Tikoo