Titan’s Variable Mesospheric Thermal Structure as Measured by ALMA

Abstract:

Temperatures in the upper atmosphere (~600-1500 km) of Titan were previously measured through the Ion and Neutral Mass Spectrometer (INMS) and Ultraviolet Imaging Spectrometer (UVIS) instruments onboard the Cassini spacecraft, showing large variability as a result of atmospheric waves, solar EUV heating, and interactions with Saturn’s magnetosphere [e.g. 1,2]. Recent observations of Titan with the Atacama Large Millimeter/submillimeter Array (ALMA) enabled the measurement of Titan’s thermal structure throughout the stratosphere and mesosphere (~80-800 km) through the retrieval of vertical temperature profiles from rotational transitions of CO [3] and HCN, including detection of a distinct mesopause near 800 km [4]. Here, we examine the variability of Titan’s mesospheric temperatures through the analysis of ALMA archival observations of CO and HCN spanning from 2012-2017, allowing for an investigation of temporal and meridional variations of Titan’s mesopause during Titan’s northern spring and summer. The determination of Titan’s mesospheric temperature structure with ALMA complements previous measurements made at similar altitudes through UVIS stellar occultations and in the thermosphere by the INMS, and provides important seasonal constraints for dynamical and circulation models of Titan’s atmosphere.

References:
[1] Koskinen et al. (2011), Icarus, 216, 507-534.

[2] Snowden et al. (2013), Icarus, 226, 552-582.

[3] Thelen et al. (2018), Icarus, 307, 380-390.

[4] Lellouch et al. (2019), Nature Astronomy, 3, 614-619.