Fig. 1. Pickup ion observation by KAGUYA above the Moon.

(A) Schematic view of the observation in the Selenocentric Solar Ecliptic coordinates. The solar wind (SW) blows around to the –x direction. Two ion sensors, IEA and IMA, on the three-axis stabilized KAGUYA measure mainly solar wind ions and ions emitted from the lunar surface and exosphere, respectively. The solar wind electric and magnetic fields (E and B) transport (pickup) ions emitted from the Moon. The length, L, between the points of origin of measured pickup ions and spacecraft’s positions is determined by L = κ/∣E∣, where κ indicates the measured ion energies. Blue arrows denote fluxes of pickup ions. (B) Schematic of C⁺ emissions due to the solar wind, solar UV, and micrometeoroids. Secondary C⁺ emitted from the surface and photoionized exospheric C⁺ are picked up by the solar wind to space. The solar wind and micrometeoroids supply carbon to the lunar surface. Indigenous carbon contained in the lunar surface and interior materials contribute substantially to C⁺ emissions.