期刊
PLANETARY AND SPACE SCIENCE
卷 57, 期 14-15, 页码 1857-1865出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.pss.2009.07.014
关键词
Titan's ionosphere; Cassini; Heavy molecular ions; Titan aeronomy; Aerosol formation; Ionospheric physics
资金
- Swedish National Space Board (SNSB)
- EU/EUROPLANET
- International Space Science Institute (ISSI)
- STFC [PP/E001173/1] Funding Source: UKRI
- Science and Technology Facilities Council [PP/E001173/1] Funding Source: researchfish
- UK Space Agency [PP/D00084X/1] Funding Source: researchfish
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 similar to 10(5)similar to 10(6) heavy positively charged ions/m(3)/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. (C) 2009 Elsevier Ltd. All rights reserved.
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