Open AccessCharged nanograins in the Enceladus plume
Author(s) -
Hill T. W.,
Thomsen M. F.,
Tokar R. L.,
Coates A. J.,
Lewis G. R.,
Young D. T.,
Crary F. J.,
Baragiola R. A.,
Johnson R. E.,
Dong Y.,
Wilson R. J.,
Jones G. H.,
Wahlund J.E.,
Mitchell D. G.,
Horányi M.
Publication year - 2012
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 - 10.1029/2011ja017218
Subject(s) - enceladus , plume , plasma , langmuir probe , magnetosphere , physics , range (aeronautics) , charged particle , electron density , spacecraft charging , population , satellite , astrophysics , atomic physics , astronomy , ion , plasma diagnostics , materials science , meteorology , nuclear physics , demography , quantum mechanics , sociology , composite material
There have been three Cassini encounters with the south‐pole eruptive plume of Enceladus for which the Cassini Plasma Spectrometer (CAPS) had viewing in the spacecraft ram direction. In each case, CAPS detected a cold dense population of heavy charged particles having mass‐to‐charge ( m / q ) ratios up to the maximum detectable by CAPS (∼10 4 amu/ e ). These particles are interpreted as singly charged nanometer‐sized water‐ice grains. Although they are detected with both negative and positive net charges, the former greatly outnumber the latter, at least in the m / q range accessible to CAPS. On the most distant available encounter (E3, March 2008) we derive a net (negative) charge density of up to ∼2600 e /cm 3 for nanograins, far exceeding the ambient plasma number density, but less than the net (positive) charge density inferred from the RPWS Langmuir probe data during the same plume encounter. Comparison of the CAPS data from the three available encounters is consistent with the idea that the nanograins leave the surface vents largely uncharged, but become increasingly negatively charged by plasma electron impact as they move farther from the satellite. These nanograins provide a potentially potent source of magnetospheric plasma and E‐ring material.