Solar-wind and interplanetary electron measurements on the Apollo 15 subsatellite

Measurements of high-energy solar-wind electrons have been made from a low orbit around the moon. Solar-wind electrons can be identified up to energies of ∼3000 ev, at which an electron population of entirely different characteristics becomes dominant. The solar-wind cavity on the moon's antisolar side shows evidence of being filled by plasma coming from the downstream direction. When the direction of the interplanetary field corresponds to solar ecliptic azimuth angles of about 90°, a partial solar-wind cavity extends across most of the eastern sunlitside of the moon within ∼20° of the noon meridian. There are localized increases in the ∼500-ev electron flux over much of the sunlit hemisphere. These increases are highly persistent and stable in their location over a 2½-day period and hence are not due to intrinsic variations in the solar wind. They are usually associated with disturbances in the magnetic field. These increases are interpreted to be the result of an interaction between the solar wind and the moon that deflects some of the solar-wind flow and results in limb shocks.