Open AccessPickup ion distributions from three‐dimensional neutral exospheres
Author(s) -
Hartle R. E.,
Sarantos M.,
Sittler E. C.
Publication year - 2011
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011ja016859
Subject(s) - physics , ion , atomic physics , gyroradius , plasma , neutral particle , distribution function , phase space , solar wind , venus , computational physics , nuclear physics , astrobiology , thermodynamics , quantum mechanics
Pickup ions formed from ionized neutral exospheres in flowing plasmas have phase space distributions that reflect their source's spatial distributions. Phase space distributions of the ions are derived from the Vlasov equation with a delta function source using three‐dimensional neutral exospheres. The ExB drift produced by plasma motion picks up the ions while the effects of magnetic field draping, mass loading, wave particle scattering, and Coulomb collisions near a planetary body are ignored. Previously, one‐dimensional exospheres were treated, resulting in closed form pickup ion distributions that explicitly depend on the ratio r g /H, where r g is the ion gyroradius and H is the neutral scale height at the exobase. In general, the pickup ion distributions, based on three‐dimensional neutral exospheres, cannot be written in closed form, but can be computed numerically. They continue to reflect their source's spatial distributions in an implicit way. These ion distributions and their moments are applied to several bodies, including He + and Na + at the Moon, H 2 + and CH 4 + at Titan, and H + at Venus. The best places to use these distributions are upstream of the Moon's surface, the ionopause of Titan, and the bow shock of Venus.