Premium
In‐situ observations of a neutral gas torus at Europa
Author(s) -
Lagg A.,
Krupp N.,
Woch J.,
Williams D. J.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2003gl017214
Subject(s) - physics , torus , jupiter (rocket family) , pitch angle , proton , orbit (dynamics) , spacecraft , neutral particle , atomic physics , astronomy , nuclear physics , plasma , geometry , mathematics , engineering , aerospace engineering
A persistent pattern in the pitch angle distributions of energetic protons near the orbit of Europa has been observed with the Energetic Particles Detector (EPD) on board the Galileo spacecraft during each of the Europa orbit crossings in the last 7 years. The proton fluxes at energies larger than 220 keV peak at equatorial pitch angles of 90° whereas fluxes of lower energy protons (80–220 keV) at this pitch angle are depleted. We propose that a Jupiter‐surrounding neutral gas torus in the vicinity of the orbit of Europa is responsible for the depletion of energetic particle fluxes by charge exchange collisions. In order to reproduce the observed depletion signature an average neutral number density of 20 to 50 cm −3 is required.