Earth Planets Space, Vol. 57 (No. 4), pp. 281-289, 2005
Shoichiro Yokota1 and Yoshifumi Saito1
1Institute of Space and Astronautical Science, Kanagawa 229-8510, Japan
(Received August 30, 2004; Revised February 1, 2005; Accepted March 10, 2005)
In situ measurement of Moon-originating ions picked-up in orbit round the Moon is expected to provide valuable information regarding the thin lunar atmosphere and surface. Secondary ions sputtered by the solar wind ions reflect the surface abundance. Global composition mapping of the lunar surface may be thus achieved by measuring the sputtered ions as one would perform laboratory SIMS. We studied the dynamics of picked-up lunar ions when the Moon was exposed to the solar wind. Our model's source mechanism involved photoionization of the lunar exospheric atoms, photon-stimulated ion desorption, and ion sputtering. We propose that an intense flux of picked-up lunar ions (104 /cm2 sec) exists at an altitude of 100 km, for nearly a quarter of the orbit. The ion flux originating from the lunar surface is mono-directional and mono-energetic, and is distinguishable from that of lunar atmospheric origin whose energy spectra correspond to their spatial distribution. Our calculation suggested that ion measurements in orbit round the Moon enable remote SIMS analyses.
Key words: Picked-up lunar ions, lunar surface, compositional remote SIMS analysis.