Discrete classification and electron energy spectra of Titan's varied magnetospheric environment

Abstract

We analyse combined electron spectra across the dynamic range of both Cassini electron sensors in order to characterise the background plasma environment near Titan for 54 Cassini‐Titan encounters as of May 2009. We characterise the encounters into four broad types: Plasma sheet, Lobe‐like, Magnetosheath and Bimodal. Despite many encounters occurring close to the magnetopause only two encounters to date were predominantly in the magnetosheath (T32 and T42). Bimodal encounters contain two distinct electron populations, the low energy component of the bi‐modal populations is apparently associated with local water group products. Additionally, a hot lobe‐like environment is also occasionally observed and is suggestively linked to increased local pick‐up. We find that 34 of 54 encounters analysed are associated with one of these groups while the remaining encounters exhibit a combination of these environments. We provide typical electron properties and spectra for each plasma regime and list the encounters appropriate to each.

Pitch angle distributions of energetic electrons at Saturn

“…If the orbit of Titan marks the approximate magnetopause Rymer et al, 2009], then mapping Titan's orbit to the ionosphere very crudely suggests that the aurora itself does mark the open/closed boundary.…”

“…Pitch angle distributions of lower-energy electrons (E < 26 keV) have been surveyed using data from the Cassini Plasma Spectrometer (CAPS) [Young et al, 2004]. These electrons exhibited butterfly, pancake, and field-aligned distributions that were interpreted in terms of inward and outward plasma motion driven by the centrifugal interchange instability in combination with azimuthal gradient and curvature drift [Rymer et al, 2009]. A preliminary report on the pitch angle distributions of energetic electrons indicated that magnetospheric electron (bidirectional) beams connect to the expected locations of Saturn's aurora [Saur et al, 2006].…”

The orientation of Titan’s dayside ionosphere and its effects on Titan’s plasma interaction

“…The electron impact rates used in this study are based on the CAPS electron fluxes measured during the TA encounter. The electron spectrum during this encounter is classified by Rymer et al (2009) as a plasma sheet encounter. The peak electron energies in this region run between 120-600 eV with the fluxes at the peak energy between 3.5 × 10 5 and 1.2 × 10 6 cm −2 s −1 sr −1 Rymer et al (2009).…”

“…The electron spectrum during this encounter is classified by Rymer et al (2009) as a plasma sheet encounter. The peak electron energies in this region run between 120-600 eV with the fluxes at the peak energy between 3.5 × 10 5 and 1.2 × 10 6 cm −2 s −1 sr −1 Rymer et al (2009). Using electron production rates based on the higher end of these ranges would increase the nightside ionospheric densities and hence the ion loss from that region.…”

“…These different orientations lead to different plasma conditions at Titan (cf. Wolf and Neubauer, 1982;Cravens et al, 1998;Ledvina and Cravens, 1998;Ledvina et al, 2004a;Bertucci et al, 2009;Rymer et al, 2009).…”