Earth Planets Space, Vol. 60 (No. 4), pp. 425-431, 2008
Hideaki Okuno, Yuta Yamanoi, and Kazuto Saiki
Department of Earth and Space Science, Graduate School of Science, Osaka University, Osaka 560-0043, Japan
(Received February 2, 2007; Revised October 5, 2007; Accepted November 22, 2007; Online published April 9, 2008)
The Mg-number [Mg# = atomic Mg/(Mg+Fe)] serves as an important petrologic discriminator when analyzing and understanding lunar rocks. Variations in the Mg# shift the wavelength of the absorption spectra of ferrous iron, which peak at around 1000 nm. Based on the image cubes of the Moon obtained by the Advanced Lunar Imaging Spectrometer (ALIS), we detected the shift in the absorption spectra of ferrous iron and built up an absorption-peak map of Mare Serenitatis. The wavelength of the absorption peak shows an 11-nm shift in Mare Serenitatis. Since the degree of space weathering can be considered to be almost the same as that within the same lava unit and Ca content cannot change without changing Mg# during magma differentiation, these shifts of the peak absorption spectra suggest that there is Mg# variation in at least the same lava unit.
Key words: Moon, hyper-spectral telescope, Mg-number.