کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1781942 | 1523969 | 2009 | 9 صفحه PDF | دانلود رایگان |
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.
Journal: Planetary and Space Science - Volume 57, Issues 14–15, December 2009, Pages 1857–1865