Survey of Galileo Plasma Observations in Jupiter's Plasma Sheet

• Published in: Journal of geophysical research. Planets Vol. 121; no. 5; pp. 871 - 894
• Main Authors: Bagenal, Fran, Wilson, Robert J., Siler, Scott, Paterson, William R., Kurth, William S.
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center American Geophysical Union 01-05-2016; Blackwell Publishing Ltd
• Subjects: Adiabatic flow; Astrophysics; Cassini mission; Constants; Corotation; Density; Galileo; Galileo spacecraft; Geophysics; Ion temperature; Jupiter; Magnetic fields; Mathematical models; Moons; Numerical Analysis; Orbits; Plasma; Spacecraft
• DOI: 10.1002/2016JE005009
• EISSN: 2169-9100
• ISSN: 2169-9097

The plasma science (PLS) Instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between approx. 5 and 30 Jupiter radii [R(sub J)] in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from approx. 2 to 3000 cm(exp.-3) at 6R(sub j) to approx. 0.05cm(sub -3) at 30 R(sub j). The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where TI is approx.60-80 eV) at approx. 6R(sub j) to a few keV at 30R(sub j).There does not seem to be a long-term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System Ill variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 R(sub j).