A Portable Magnetometer for Magnetic Measurements of Meter‐Sized Meteorites

Abstract

Meteorites contain records of past magnetic fields in the form of natural remanent magnetization (NRM). A key property of meteorite magnetization that provides information about its origin is its dependence on spatial scale. In particular, understanding how the mean remanent magnetization varies from the scale of meteorites to the global scale of their parent bodies would aid in the interpretation of spacecraft magnetometry data. However, the vast majority of meteorite samples whose remanent magnetization have been measured have sizes <10 cm due to the limited size range accommodated by laboratory magnetometers. To address this limitation, we developed a portable magnetometer array that enables remanence measurements of meter-size meteorites in a non-magnetically shielded environment. The instrument measures both NRM and induced magnetization using two orthogonal square Helmholtz coil pairs that compensate the vertical and horizontal components of the background magnetic field. An array of four magnetometers mounted on a movable aluminum rail measures the magnetic field at multiple locations around the sample. The instrument is transportable and can be adapted to different sample sizes. After distinguishing the induced component from the remanent component of a sample's total field, the remanence can be estimated from a multipole field inversion combined with nonlinear least squares method. We validated the instrument and data processing on a magnet of known magnetic moment and measured the NRM of a meter-sized iron meteorite.