Author/Authors :
Wahlund، نويسنده , , J.-E. and Galand، نويسنده , , M. and Müller-Wodarg، نويسنده , , I. and Cui، نويسنده , , J. and Yelle، نويسنده , , R.V. and Crary، نويسنده , , F.J. and Mandt، نويسنده , , K. A. Magee، نويسنده , , B. and Waite Jr.، نويسنده , , J.H. and Young، نويسنده , , D.T. and Coates، نويسنده , , A.J. and Garnier، نويسنده , , P. and إgren، نويسنده , , K. and André، نويسنده , , M. and Eriksson، نويسنده , , A.I. and Cravens، نويسنده , , T.، نويسنده ,
Abstract :
We present observational evidence that the ionosphere of Titan below an altitude of 1150 km is a significant source of heavy (>100 amu) molecular organic species. This study is based on measurements by five instruments (RPWS/LP, RPWS/E, INMS, CAPS/ELS, CAPS/IBS) onboard the Cassini spacecraft during three flybys (T17, T18, T32) of Titan. The ionospheric peaks encountered at altitudes of 950–1300 km had densities in the range 900–3000 cm−3. Below these peaks the number densities of heavy positively charged ions reached 100–2000 cm−3 and approached 50–70% of the total ionospheric density with an increasing trend toward lowest measured altitudes. Simultaneously measured negatively charged ion densities were in the range 50–150 cm−3. These results imply that ~105–106 heavy positively charged ions/m3/s are continuously recombining into heavy neutrals and supply the atmosphere of Titan. The ionosphere may in this way produce 0.1–1 Mt/yr of heavy organic compounds and is therefore a sizable source for aerosol formation. We also predict that Titanʹs ionosphere is dominated by heavy (>100 amu) molecular ions below 950 km.
Keywords :
Titanיs ionosphere , Cassini , Heavy molecular ions , Titan aeronomy , Aerosol formation , Ionospheric physics
