Plasma temperatures in Saturn's ionosphere

Abstract

We have calculated self‐consistent electron and ion temperatures in Saturn's ionosphere using a series of coupled fluid and kinetic models developed to help interpret Cassini observations and to examine the energy budget of Saturn's upper atmosphere. Electron temperatures in the midlatitude topside ionosphere during solar maximum are calculated to range between 500 and 560 K during the Saturn day, approximately 80–140 K above the neutral temperature. Ion temperatures, calculated for only the major ions H+ and H3+, are nearly equal to the neutral temperature at altitudes near and below the height of peak electron density, while they can reach 500 K during the day at the topside. Plasma scale heights of the dusk electron density profile from radio occultation measurements of the Voyager 2 flyby of Saturn have been used to estimate plasma temperature as a comparison. Such an estimate agrees well with the temperatures calculated here, although there is a topside enhancement in electron density that remains unexplained by ionospheric calculations that include photochemistry and plasma diffusion. Finally, parameterizations of the heating rate from photoelectrons and secondary electrons to thermal, ambient electrons have been developed. They may apply for other conditions at Saturn and possibly at other giant planets and exoplanets as well.

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

“…We included the latter by using a suprathermal electron transport model adapted to EGPs that is based on the solution to the Boltzmann equation with transport, angular scattering, and energy degradation of photo-electrons and their secondaries taken into account. For further information on the suprathermal electron transport model, see Moore et al (2008) and Galand et al (2009). We assumed here that the source of incident energy is solar or stellar XUV radiation.…”

Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra

“…Kim and Fox 1991;Moses and Bass 2000). Ionospheric models have been developed for the outer planets, as reviewed by with more recent models proposed for Jupiter (Achilleos et al 1998;Perry et al 1999;Grodent et al 2001;Millward et al 2002;Tao et al 2010;Barrow and Matcheva 2011) and Saturn (Moses and Bass 2000;Moore et al 2004Moore et al , 2006Moore et al , 2008Moore et al , 2010Galand et al 2009Galand et al , 2011Barrow and Matcheva 2013).…”

Diurnal variation of electron density in Saturn’s ionosphere: Model comparisons with Saturn Electrostatic Discharge (SED) observations

“…These modules include photochemistry, plasma diffusion (Moore et al, 2004), shadowing due to Saturn's rings (Mendillo et al, 2005), and a time-variable water influx (Moore et al, 2006;Moore and Mendillo, 2007). Recently the ionospheric modules have been coupled with a 1D electron transport code in order to incorporate the effects of photoelectrons on Saturn's ionosphere (Galand et al, , 2011, including plasma temperature calculations (Moore et al, 2008), and parameterizations of the secondary ionization and thermal electron heating rates at Saturn ). Saturn's magnetic field is specified with the Saturn Pioneer Voyager (SPV) model (Davis and Smith, 1990).…”

“…STIM does not include the hundreds of reactions necessary to fully apportion accurate hydrocarbon ion fractions; rather it uses a small subset of simplified chemistry that acts predominantly as a sink for Saturn's major ions, H + and H þ 3 . Though the ultimate hydrocarbon ions in STIM's chemical scheme -CH þ 3 ; CH þ 4 , and CH þ 5 , hereafter designated CH þ X -are different from those that result from a more complete treatment (e.g., C 3 H þ 5 of Moses and Bass, 2000), the calculated electron density in the hydrocarbon region is approximately unchanged (Moore et al, 2008).…”