Electron density and temperature measurements in the cold plasma environment of Titan: Implications for atmospheric escape

Niklas Jt Edberg (1) , J.-E. Wahlund (1) , K. Agren (1) , M. W. Morooka (1) , Ronan Modolo (2) , C. Bertucci (3) , M. K. Dougherty (4)

1 IRF - Swedish Institute of Space Physics [Uppsala / Kiruna]
2 HELIOS - LATMOS
3 IAFE - Instituto de Astronomía y Física del Espacio [Buenos Aires]
4 Space and Atmospheric Physics Group [London]

We present electron temperature and density measurements of Titan's cold ionospheric plasma from the Langmuir probe instrument on Cassini from 52 flybys. An expression of the density as a function of temperature is presented for altitudes below two Titan radii. The density falls off exponentially with increased temperature as log(ne) = −2.0log(Te) + 0.6 on average around Titan. We show that this relation varies with location around Titan as well as with the solar illumination direction. Significant heating of the electrons appears to take place on the night/wake side of Titan as the density-temperature relation is less steep there. Furthermore, we show that the magnetospheric ram pressure is not balanced by the thermal and magnetic pressure in the topside ionosphere and discuss its implications for plasma escape. The cold ionospheric plasma of Titan extends to higher altitudes in the wake region, indicating the loss of atmosphere down the induced magnetospheric tail.

Mots clés: Atmospheric escape; Cassini; Temperature; Density; Titan Ionosphere

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Planétologie et astrophysique de la terre [astro-ph.EP]; Physique des plasmas [physics.plasm-ph]

Niklas Jt Edberg, J.-E. Wahlund, K. Agren, M. W. Morooka, Ronan Modolo, et al.. Electron density and temperature measurements in the cold plasma environment of Titan: Implications for atmospheric escape. Geophysical Research Letters, 2010, 37 (20), pp.L20105. ⟨10.1029/2010GL044544⟩. ⟨hal-00509063⟩