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 Titan's ionosphere is dominated by heavy (>100 amu) molecular ions below 950 km.
Original language | English (US) |
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Pages (from-to) | 1857-1865 |
Number of pages | 9 |
Journal | Planetary and Space Science |
Volume | 57 |
Issue number | 14-15 |
DOIs | |
State | Published - Dec 2009 |
Keywords
- Aerosol formation
- Cassini
- Heavy molecular ions
- Ionospheric physics
- Titan aeronomy
- Titan's ionosphere
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science