title: MESSENGER observations of the spatial distribution of planetary ions near Mercury.
abstract: Global measurements by MESSENGER of the fluxes of heavy ions at Mercury, particularly sodium (Na(+)) and oxygen (O(+)), exhibit distinct maxima in the northern magnetic-cusp region, indicating that polar regions are important sources of Mercury's ionized exosphere, presumably through solar-wind sputtering near the poles. The observed fluxes of helium (He(+)) are more evenly distributed, indicating a more uniform source such as that expected from evaporation from a helium-saturated surface. In some regions near Mercury, especially the nightside equatorial region, the Na(+) pressure can be a substantial fraction of the proton pressure.
authors.affiliation: Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA. thomasz@umich.edu
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Zurbuchen
authors.forename: Jim M
authors.initials: JM
authors.lastname: Raines
authors.forename: James A
authors.initials: JA
authors.lastname: Slavin
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Gershman
authors.forename: Jason A
authors.initials: JA
authors.lastname: Gilbert
authors.forename: George
authors.initials: G
authors.lastname: Gloeckler
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Anderson
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Baker
authors.forename: Haje
authors.initials: H
authors.lastname: Korth
authors.forename: Stamatios M
authors.initials: SM
authors.lastname: Krimigis
authors.forename: Menelaos
authors.initials: M
authors.lastname: Sarantos
authors.forename: David
authors.initials: D
authors.lastname: Schriver
authors.forename: Ralph L
authors.initials: RL
authors.lastname: McNutt
authors.forename: Sean C
authors.initials: SC
authors.lastname: Solomon