Pickup Ion Observations at Solar System Bodies

Abstract

Ion pickup is one of the fundamental processes at work throughout the solar system. The ionization of neutral gas provides fresh pickup ions which then interact with the plasma environment — e.g., the solar wind or a planetary magnetosphere. Initially the motion is acceleration along the electric field, but the presence of a magnetic field eventually causes a cycloid in real space and a ring in velocity space. Given enough time, scattering may occur in pitch angle and in energy. If there is a variation in the rate of pickup over the cycloid, nongyrotropic ion distributions can be seen. Here I review the ion pickup process and the observations at comets [Giacobini-Zinner (GZ), Halley, Grigg-Skjellerup (GS), and Borrelly], and at Mercury, Venus, Mars, in the Saturn and Jupiter systems (particularly at Titan, Enceladus, in Saturn's inner magnetosphere and at Io), and at the Moon. Results from several space missions are reviewed (ICE, Giotto, DS1, Messenger, Venus Express, Mars Express, Cassini, Galileo, Kaguya, and Chandrayaan-1). I compare the process and timescales in the various contexts and examine the prospects for future missions including Rosetta, BepiColombo, and EJSM.