Investigation of energetic proton penetration in Titan's atmosphere using the Cassini INCA instrument

Statistical analysis of the energetic ion and ENA data for the Titan environment

“…The calculation of the ionization peak altitudes for our protons energy channels, by using the Rees (1963) formula, combined with N 2 profiles from an updated version of the Toublanc et al (1995) photochemical model, leads to a significant energy deposition around 650-900 km altitude, which is consistent with the detailed studies by Luna et al (2003), Cravens et al (2008) and Smith et al (2009). We remind the reader that the pitch angle distributions (see Section 3.5) are apparently quasi-isotropic, and that their large gyroradii prevent their trajectories from being efficiently deflected away from Titan.…”

“…Cai et al, 2009). Moreover, these timescales emphasize that the energetic plasma environment is highly dynamic during a single Titan flyby (as also emphasized by Smith et al, 2009 for the flyby T18): the Cassini spacecraft stays about 10 min below the exobase during typical low altitude encounters, and 5 h inside the Titan's Hill sphere radius ð $ 50,000 kmÞ which may define the extension of Titan's corona.…”

“…We concluded that the ENAs are thermalized only very deep in the atmosphere (around or below 1000 km altitude), but that their emission lower limit is around the exobase (H c $ 1425 km altitude) for the ENA imaging from high altitudes, implying an ENAs halo centered around 2000 km altitude after the instrumental scattering (see for more details). We may add that Smith et al (2009) recently studied the energy deposition in Titan's atmosphere by energetic protons, during one specific flyby and using INCA results. This paper is dedicated to the analysis of the Cassini MIMI data (mostly LEMMS and INCA) for the Titan environment, during the first years of the Cassini mission in orbit around Saturn.…”

“…Thus, the energetic protons will deposit much energy down to low altitudes. Cravens et al (2008) and Smith et al (2009) investigated recently the energy deposition into Titan's atmosphere by energetic protons, using LEMMS proton fluxes measured during specific flybys, i.e. T5 and T18.…”

Science goals and mission concept for the future exploration of Titan and Enceladus

“…These ions impact Titan's thermosphere primarily heating the thermosphere, but also ionizing the local gas (Westlake et al, 2011;Shah 29 et al, 2009;Smith et al, 2009). The oxygen and water group ions in the 1-100 keV range are most efficient at heating the thermosphere (Shah et al, 2009), while protons deposit their energy below the homopause ).…”