title: Planetary science. Low-altitude magnetic field measurements by MESSENGER reveal Mercury's ancient crustal field.
abstract: Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada. Planetary Science Institute, Tucson, AZ 85719, USA. cjohnson@eos.ubc.ca.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Johnson
authors.affiliation: Planetary Science Directorate, Southwest Research Institute, Boulder, CO 80302, USA.
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Phillips
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Purucker
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Anderson
authors.affiliation: Lunar and Planetary Institute, Houston, TX 77058, USA. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
authors.forename: Paul K
authors.initials: PK
authors.lastname: Byrne
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
authors.forename: Brett W
authors.initials: BW
authors.lastname: Denevi
authors.affiliation: Institute for Rock Magnetism, Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Feinberg
authors.affiliation: Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Hauck
authors.affiliation: Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA.
authors.forename: James W
authors.initials: JW
authors.lastname: Head
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
authors.forename: Haje
authors.initials: H
authors.lastname: Korth
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: James
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
authors.forename: Erwan
authors.initials: E
authors.lastname: Mazarico
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Neumann
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
authors.forename: Lydia C
authors.initials: LC
authors.lastname: Philpott
authors.affiliation: Planetary Science Institute, Tucson, AZ 85719, USA. Department of Earth Sciences, Southern Methodist University, Dallas, TX 75205, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Siegler
authors.affiliation: Institute and Faculty of Physics, Saint Petersburg State University, Saint Petersburg, Russia.
authors.forename: Nikolai A
authors.initials: NA
authors.lastname: Tsyganenko
authors.affiliation: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Solomon