Although the Moon today has no global magnetic field, paleomagnetic measurements of Apollo samples indicate the existence of an ancient field from at least 4.25 to 1.92 billion years ago. It has been proposed that the paleofield was generated by a core dynamo. However, the paleofield’s apparent high intensity and longevity are major challenges to current theory. Three key difficulties have been that the paleofield intensity has been poorly constrained, while the paleofield’s lifetime and direction have been essentially unknown. To address this, I describe three key new types of paleomagnetic measurements. First, enabled by our new controlled oxygen fugacity thermal demagnetization system, I report some of the first accurate lunar paleointensity measurements. Second, I present young paleointensities to constrain the end of the field’s lifetime. Finally, I report a robust constraint on the field’s paleodirection from Apollo 17 basalt flows (see photo below). The data collectively support the existence of an intense early dynamo powered by an unusually energetic mechanism like precession, followed by a weaker long-lived dynamo perhaps powered by core crystallization. The paleodirectional data are consistent with but do not require a Moon-centric axial dipole geometry like that of the Earth.
BIO
Benjamin Weiss is the Robert R. Shrock Professor of Earth and Planetary Sciences and is the Chair of the Program in Planetary Science in the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology (MIT). He joined the MIT faculty in 2004 after completing his Ph.D. at the California Institute of Technology (Caltech). He directs the MIT Planetary Magnetism Laboratory, which studies the paleomagnetism of samples from Earth, Moon, Mars and asteroids. Weiss is the Deputy Principal Investigator and Magnetometry Investigation Lead on the Psyche mission and Co-investigator on the Mars 2020 rover and the Europa Clipper missions. He is a member of the U.S. National Academy of Sciences and received the American Geophysical Union’s James B. Macelwane Medal and Caltech’s Francis and Milton Clauser Doctoral Prize.
Host: Xuening Bai
