title: A long-lived lunar core dynamo.
abstract: Paleomagnetic measurements indicate that a core dynamo probably existed on the Moon 4.2 billion years ago. However, the subsequent history of the lunar core dynamo is unknown. Here we report paleomagnetic, petrologic, and (40)Ar/(39)Ar thermochronometry measurements on the 3.7-billion-year-old mare basalt sample 10020. This sample contains a high-coercivity magnetization acquired in a stable field of at least ~12 microteslas. These data extend the known lifetime of the lunar dynamo by 500 million years. Such a long-lived lunar dynamo probably required a power source other than thermochemical convection from secular cooling of the lunar interior. The inferred strong intensity of the lunar paleofield presents a challenge to current dynamo theory.
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
authors.forename: Erin K
authors.initials: EK
authors.lastname: Shea
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Weiss
authors.forename: William S
authors.initials: WS
authors.lastname: Cassata
authors.forename: David L
authors.initials: DL
authors.lastname: Shuster
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Tikoo
authors.forename: Jérôme
authors.initials: J
authors.lastname: Gattacceca
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Grove
authors.forename: Michael D
authors.initials: MD
authors.lastname: Fuller