Remanent magnetization of the lunar surface

Abstract

Two lines of evidence support each other in suggesting that a large volume of the rocks near the lunar surface possess a uniform remanent magnetization with an intensity of about 2 x 10- 6 emu/g. The first line is the discovery by several groups of investigators of weak but stable remanent magnetizations in igneous samples returned from the first four Apollo missions. Although the mechanism of acquisition of this remanence has not been definitely established, several lines of evidence, including thermal demagnetization, suggest that it is a thermoremanent magnetization (TRM) carried by iron. Many of the breccias are similarly magnetized. The second line is the measurement of significant fields at the Apollo sites and the discovery of large-scale anomalies by the subsatellite magnetometer experiment. It appears that magnetized rocks are the source for these fields, and simple model calculations suggest that the magnetization typical of mare basalt can account for these features.