Kim, Kyeong - the Moon and Asteroids

Abstract: 
Gamma ray spectrometry (GRS) allows us to characterize the elemental composition of the upper tens centimeters of solid planetary surfaces. High energy resolution gamma ray data were firstly obtained by the Kaguya Gamma-Ray Spectrometer (KGRS). Elemental maps generated on the basis of the KGRS include natural radioactive elements (K, Th, U) as well as major elements maps (e.g., Ca and Al). The elemental maps of Si, Fe, and Ti were recently investigated. Analysis of the Si gamma ray has been investigated using the 4934 keV Si peak produced by the thermal neutron interaction 28Si(n,g)29Si, generated during the interaction of galactic cosmic rays and surface material containing Si. The emission rate of gamma rays is directly proportional to the abundance of Si from the lunar surface; however, it is also affected by the thermal neutron density in the lunar surface. For the correction associated with neutron effect on the Si gamma ray data, we used the relative variation in global distribution of thermal neutron flux measured by Lunar Prospector. Normalization of Si elemental abundance using the KGRS data was accomplished using Apollo returned sample data. The normalized Si elemental abundance of the KGRS data ranged from about 15 to 27% Si. The lowest and highest SiO2 abundance correspond to mineral groups like pyroxene group (PKT region) and feldspar group (Northern highlands), respectively. Our elemental map of Si derived from KGRS data shows that the highland areas of both nearside and farside of the Moon have higher abundance of Si, and the mare regions of the nearside of the Moon have the lowest Si abundance on the Moon. Our study clearly shows that there are a number of Si enriched areas compared to that of Apollo 16 site. This result is similar to the mineralogical data obtained by Diviner. The feldspathic highland areas are confirmed through the elemental map of Si by the KGRS data. When the Si map of KGRS data is compared with the LRO's mineralogical map, a reasonable agreement in understanding of the dichotomy between lunar mafic and feldspathic regions of the moon is confirmed. This presentation also includes a brief introduction to the preliminary results of Fe and Ti elemental maps obtained by KGRS. These two elements allow us to distinguish among lunar rocks, and Ti forms the basis for classifying the basalts that make up the lunar maria. Mare basalts erupting from the interior after formation of the lunar crust and filling large basins can retain important information in concert with petrologic relationships to infer the mantle compositions of the interior. Fe and Ti contents in mare regions are much higher than those in highlands. Especially high concentration of Ti on Mare Tranquillitatis is confirmed.