Determining ion mobility spectra of Titan's lower atmosphere
Abstract
Ion mobility spectra for Titan's lower atmosphere have been obtained by two differing methods; theoretical predictions and extracting data from the Huygens HASI relaxation probe. The first method is to apply an equation relating the size of an ion to its electric mobility to the conditions on Titan for a set of predicted ions. The average mobility for predicted positive ions at the surface of Titan is estimated to be 0.74 ± 0.01 cm2 V-1 s-1 , where the most abundant predicted species are CH+ CH4 , HCO+ H2 , 5 HCNH+ C2 H4 and C7 H+ . Atmospheric conductivity calculated from the mobility estimates agrees well with previously predicted conductivity profiles. Mobility spectra have been produced for the set of predicted positive and negative ions. Ion mobility spectra can also be extracted from relaxation probe measurements. This technique has been applied to the disc-shaped relaxation probes of the Huygens HASI instrument, which measured the atmospheric conductivity of Titan. An average mobility spectrum has been extracted from Huygens data for negative ions between 81.9km and 84.8km. The mean mobility of negative ions contributing to atmospheric conductivity in this region was found to be 101 ± 21 cm2 V-1 s-1 and the negative conductivity was calculated as (14 ± 3) pSm-1 . Peaks in the extracted mobility spectrum at 76, 86 and 102 cm2 V-1 s-1 are consistent with the mobilities of postulated negative species, propyne (C3 H- ), ethyne (C2 H- ) and methane (CH- ) respectively. 2 3
- Publication:
-
European Planetary Science Congress 2006
- Pub Date:
- 2006
- Bibcode:
- 2006epsc.conf..156O