The Randolph Bromery Fall 2018 Seminar Series

Description

Beck Strauss from the National Institute of Standards and Technology will present "The Case of the Missing Dynamo: Constraining the Decline of the Moon's Magnetic Field" as part of the Randolph Bromery Fall 2018 Seminar Series.

Abstract:

From stalagmites to meteorites, rocks hold a wealth of information about the planetary magnetic fields in which they form. The magnitudes and orientations of these fields can vary over geologic time due to changing conditions in planetary interiors. By studying dynamo fields like that of the Earth's Moon, we can learn about the deep interiors and histories of other planets.

Magnetic studies of lunar samples from the Apollo missions indicate that the Moon generated a core dynamo field between at least 4.25 and 2.5 Ga. A high field period 3.85-3.56 Ga was followed by a dramatic decline in surface field intensity by 3.19 Ga, leaving the field in a weakened state until its demise. The change from a high field state to a low field state suggests a change in the mechanism of field generation. However, the poor magnetic properties of most lunar rocks have hindered prior attempts to retrieve information from those magnetized in weak fields < 3.56 Ga.

Vitrophyric basalts cooled at faster rates than more crystalline basalts and thus may contain smaller magnetic grains capable of recording weaker fields. We analyzed the magnetic properties of three vitrophyre basalt samples collected during the Apollo 12 mission in order to constrain the behavior of the Moon's dynamo field near the end of its initial decline while exploring the relationship between magnetic recording and grain size in lunar rocks.