Observation of energetic lunar pick-up ions near earth

Abstract

Singly ionized suprathermal lunar pick-up ions were observed upstream of the earth's bow shock between August and December 1985 using the time-of-flight spectrometer SULEICA on the AMPTE/IRM satellite. The pick-up ions move on cyclodial trajectories in a plane perpendicular to the interplanetary magnetic field (IMF) and can be observed when this plane includes the moon-satellite line. The detection of heavy pickup ions is only possible with the instrument when they possess almost the maximum of their pickup energy and thus depends on the gyro phase of the incoming ions. Therefore, their detection is critically dependent on the orientation and strength of the IMF, the solar wind velocity and the orientation of the tangent of the cyclodial motion with respect to the instrument aperture. As a result the flux of the ions is highly anisotropic and preferably oriented along the moon-satellite line within an angular range of about 30°. Under these constraints a minimum flux level of 0.3 cm −2 sec −1 sr −1 keV −1 can be given for the ions in the mass range between 23 and 37 amu.