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

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.

[1]  Donald A. Gurnett,et al.  Titan's ionosphere in the magnetosheath : Cassini RPWS results during the T32 flyby , 2009 .

[2]  M. L. Kaiser,et al.  The Cassini Radio and Plasma Wave Investigation , 2004 .

[3]  P. Bernhardt,et al.  Self‐consistent modeling of equatorial dawn density depletions with SAMI3 , 2010 .

[4]  Thomas E. Cravens,et al.  Energetic ion precipitation at Titan , 2008 .

[5]  J. H. Waite,et al.  Composition of Titan's ionosphere , 2006 .

[6]  K.-H. Glassmeier,et al.  The Cassini Magnetic Field Investigation , 2004 .

[7]  Nicholas Achilleos,et al.  Titan's Magnetic Field Signature During the First Cassini Encounter , 2005, Science.

[8]  J. Wahlund,et al.  On the amount of heavy molecular ions in Titan's ionosphere , 2009 .

[9]  D. Young,et al.  Discrete classification and electron energy spectra of Titan's varied magnetospheric environment , 2009 .

[10]  T. Hill,et al.  Ionospheric electrons in Titan's tail: Plasma structure during the Cassini T9 encounter , 2007 .

[11]  M. Acuna,et al.  The induced magnetosphere of Titan , 1982 .

[12]  Panayotis Lavvas,et al.  Diurnal variations of Titan's ionosphere , 2009 .

[13]  P. Canu,et al.  On magnetospheric electron impact ionisation and dynamics in Titan's ram-side and polar ionosphere – a Cassini case study , 2007 .

[14]  Donald A. Gurnett,et al.  Plasma environment in the wake of Titan from hybrid simulation: A case study , 2007 .

[15]  S. Asmar,et al.  Possible Detection of Titan's Ionosphere from Voyager 1 Radio Occultation Observations , 1995 .

[16]  P. Canu,et al.  Cassini Measurements of Cold Plasma in the Ionosphere of Titan , 2005, Science.

[17]  J. Wahlund,et al.  On the ionospheric structure of Titan , 2009 .

[18]  M. Dougherty,et al.  Comparisons between MHD model calculations and observations of Cassini flybys of Titan , 2006 .

[19]  M. Dougherty,et al.  Cold ionospheric plasma in Titan's magnetotail , 2007 .

[20]  J. Waite,et al.  Ion transport in Titan's upper atmosphere , 2010 .