Premium
Survey of Thermal Plasma Composition in Saturn's Magnetosphere Using Time‐of‐Flight Data From Cassini/CAPS
Author(s) -
Felici M.,
Arridge C. S.,
Wilson R. J.,
Coates A. J.,
Thomsen M.,
Reisenfeld D.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2017ja025085
Subject(s) - magnetosphere of saturn , magnetosphere , saturn , physics , enceladus , titan (rocket family) , plasma , astrobiology , plasma sheet , icy moon , astronomy , ion , astrophysics , planet , magnetopause , nuclear physics , quantum mechanics
The Cassini spacecraft orbited Saturn from 2004 to 2017, and in 2006 it started exploring the deep magnetotail, reaching distances of about 68 R S (where R S is the equatorial radius of Saturn). Since Cassini covered a broad area of Saturn's magnetosphere, this raises the question of what is the typical and atypical plasma composition in different regions of Saturn's environment. In this paper, we present a survey of the bulk plasma composition using time‐of‐flight data from the Plasma Spectrometer/Ion Mass Spectrometer instrument on Cassini, from 2004 through 2012. This is the most comprehensive study ever made of relative abundances of thermal plasma at Saturn, maximizing the use of Cassini's orbital coverage in Saturn's magnetosphere during those years, and, therefore, the sensitivity to seasonal or natural variability of the system. We studied the ratio of counts between ions with E / q ≃1.19–21,300 eV/q and mass per charge equal to 2 (either H2 +or He ++ ) and ionized hydrogen ([( m / q = 2)]/[H + ]), and a mixture of ions (H 2 O + , H 3 O + , OH + , and O + ), known as the water group (W + ) and ionized hydrogen ([W + ]/[H + ]). We present the data as a function of position in the magnetosphere, radial distance and local time, and distance from the planet and longitude with respect to the moons Enceladus, Dione, Rhea, and Titan. We found that the plasma composition in Saturn's magnetosphere presents significant local time asymmetries and variability.