סמינר מיוחד בחוג למדעי כדור הארץ: The Moon, Impacts and the Solar wind: Can impact-generated vapor clouds be responsible for magnetization on the Moon?
Rona Oran, MIT
Measurements of the lunar magnetic field have revealed a crustal field that varies in magnitude and direction over length scales as small as tens of kilometers. The source of these magnetic anomalies remains a mystery. A key question is whether the crustal magnetization is a record of a hypothetical ancient dynamo field (that has since cooled off), or whether external transient fields are the source of magnetization. This distinction between internal or external sources for the magnetization has broad implications to our understanding of the Moonʼs history and current internal structure. Further, the lunar crustal field serves as a test case for understanding remnant magnetization of other solar system bodies,such as Mars, Mercury and asteroids.
The identification of strong anomalies at the antipodes of four of the five youngest large impact basins led to the theory that the magnetization is due to transient external fields created by the impacts. These transient fields are assumed to have been created through the interaction of the vapor generated by the impact with the surrounding solar wind. In this talk, we present an examination of this hypothesis, using magnetohydrodynamic simulations. This constitutes the first direct calculation of the magnetic fields expected to be formed by this mechanism.
Preliminary results show that the vapor expansion and wind compression lead to onlymoderate field enhancements, several orders of magnitude below the required value. Based on these results we propose that impacts are probably not the cause of magnetization on the lunar crust, and that the source of magnetization is more likely to be internal.