Detection of X-ray fluorescence line feature from the lunar surface

Abstract

We present the results of an analysis by ASCA (Japanese X-ray astronomy satellite) observation of the lunar surface on July 10th – 11th, 1993. In spite of the fact that the X-ray surface brightness is estimated to be at nearly CXB (Cosmic X-ray Background) level, the X-ray spectrum shows significant deviations in relation to Al-Kα and Si-Kα fluorescence X-rays. According to the intensity ratios of Al/Si (1–2) and Mg/Si(<0.4), the properties of the X-ray spectrum is consistent with an intermediate abundance ratio between highlands and mares (or relatively similar to highland values). However, the X-ray illuminated region on the lunar surface are mainly covered with mare regions and the emission of AlK and SiK fluorescence arises from both day side and night side region of the moon. These facts indicate the existence of X-ray production due to bremsstrahlung, with high energy particles impacting even on the night side.