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Carbon chain anions and the growth of complex organic molecules in Titan's ionosphere

Desai, RT; Coates, AJ; Wellbrock, A; Vuitton, V; Crary, FJ; González-Caniulef, D; Shebanits, O; ... Sittler, EC; + view all (2017) Carbon chain anions and the growth of complex organic molecules in Titan's ionosphere. The Astrophysical Journal Letters , 844 (2) 10.3847/2041-8213/aa7851. Green open access

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Abstract

Cassini discovered a plethora of neutral and ionized molecules in Titan's ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q−1. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950–1300 km. We report on detections consistently centered between 25.8 and 26.0 u q−1 and between 49.0–50.1 u q−1 which are identified as belonging to the carbon chain anions, CN−/C3N− and/or C2H−/C4H−, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73–74 u q−1 could be attributed to the further carbon chain anions C5N−/C6H− but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at >100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below <1100 km, the low-mass anions (<150 u q−1) were found to deplete at a rate proportional to the growth of the larger molecules, a correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium.

Type: Article
Title: Carbon chain anions and the growth of complex organic molecules in Titan's ionosphere
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/2041-8213/aa7851
Publisher version: http://dx.doi.org/10.3847/2041-8213/aa7851
Language: English
Additional information: Copyright © 2017. The American Astronomical Society. All rights reserved. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Keywords: astrobiology, astrochemistry, ISM: molecules, planets and satellites: atmospheres, planets and satellites: individual (Titan)
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/1568197

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