Thorium distribution on the Moon: new insights from Chang’E-2 gamma-ray spectrometer**A contributed paper from the International Symposium on Lunar and Planetary Science (ISLPS) held on 2018 June 12–15 at Macau University of Science and Technology.

Abstract

We present the thorium distribution on the lunar surface derived from observations by the Chang’E-2 gamma-ray spectrometer (CE-2 GRS). This new map shows a similar thorium distribution to previous observations. In combination with this new thorium map and impact cratering model, we investigate the origination of thorium on the Moon’s highlands, which was previously thought to be contributed from Imbrium ejecta. We found that the Imbrium ejecta has a small contribution (∼20%–30%) to the thorium on the lunar highlands but most thorium is likely to be indigenous before the deposition of the Imbrium ejecta. This new thorium map also confirms that the eastern highlands have a relatively higher thorium concentration than the western highlands. We propose that the thin crust and large basins on the eastern highlands are responsible for this difference in thorium.