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A first look at Titan with JWST’s MIRI spectrometer

Presentation #204.06 in the session Titan II: Atmospheres (Poster + Lightning Talk)

Published onOct 23, 2023
A first look at Titan with JWST’s MIRI spectrometer

Here we explore the first spectra of Titan measured by JWST’s Mid-Infrared Instrument (MIRI) from the 1251 GTO programme [1]. We focus on medium resolution spectroscopy covering 5-28 microns, which covers emission features of many important stratospheric hydrocarbon and nitrile species (e.g., CH4, C2H2, C2H4, C2H6, C3H4, C4H2, C6H6, HCN, and HC3N) [1,2]. Observations of spatial and temporal variations of these species can be used to determine atmospheric temperature and composition, which can probe atmospheric dynamics [2-6]. For example, during the Cassini mission (2004-2017) extreme enhancements of trace gases were used to detect a reversal in the meridional circulation following the 2009 northern spring equinox [3,6]. These enrichments could play an important role in enhancing winter polar mesospheric cooling, which may explain unexpectedly low polar temperatures observed in early southern winter [4]. Titan’s southern spring equinox is in 2025 where large changes in circulation and composition are expected to occur, which we can investigate with these and subsequent observations. JWST MIRI observations have comparable spectral resolution to Cassini’s CIRS instrument, but with many orders of magnitude improvement in signal-to-noise (expected ~104-105 [1]). This will allow us to detect very weak emission lines for the first time and perhaps discover new stratospheric species to inform photochemical modelling and reveal new aspects of the dynamics. JWST’s very high signal-to-noise also somewhat offsets its low spatial resolution and will allow us to study Titan’s stratospheric temperature and composition in the critical pre-equinox period. This will allow us to test if seasonal behaviour observed by Cassini around northern spring equinox [5] is mirrored around southern spring equinox or if seasons are asymmetric due to Saturn’s orbital eccentricity. These results will have important implications for the next generation of Titan General Circulation Models [7]. [1] Nixon+ 2016, Pub. Ast. Soc. Pacific 128, 018007. [2] Flasar+ 2004, Space Sci. Rev. 115, 169–297. [3] Teanby+ 2012, Nature 491, 732–735. [4] Teanby+ 2017, Nature Comms. 8, 1586. [5] Teanby+ 2019, Geophys. Res. Lett. 46, 3079–3089. [6] Vinatier+ 2020, Astron. Astrophys. 641, A116. [7] Lombardo+Lora 2023, Icarus 390, 115291.

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