Abundance Measurements of Titan's Stratospheric HCN, HC${}_3$N, C${}_3$H${}_4$, and CH${}_3$CN from ALMA Observations

Abstract

Previous investigations have employed more than 100 close observations of Titan by the Cassini orbiter to elucidate connections between the production and distribution of Titan's vast, organic-rich chemical inventory and its atmospheric dynamics. However, as Titan transitions into northern summer, the lack of incoming data from the Cassini orbiter presents a potential barrier to the continued study of seasonal changes in Titan's atmosphere. In our previous work (Thelen et al., 2018), we demonstrated that the Atacama Large Millimeter/submillimeter Array (ALMA) is well suited for measurements of Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km) through the use of spatially resolved (beam sizes <1'') flux calibration observations of Titan. Here, we derive vertical abundance profiles of four of Titan's trace atmospheric species from the same 3 independent spatial regions across Titan's disk during the same epoch (2012 to 2015): HCN, HC${}_3$N, C${}_3$H${}_4$, and CH${}_3$CN. We find that Titan's minor constituents exhibit large latitudinal variations, with enhanced abundances at high latitudes compared to equatorial measurements; this includes CH${}_3$CN, which eluded previous detection by Cassini in the stratosphere, and thus spatially resolved abundance measurements were unattainable. Even over the short 3-year period, vertical profiles and integrated emission maps of these molecules allow us to observe temporal changes in Titan's atmospheric circulation during northern spring. Our derived abundance profiles are comparable to contemporary measurements from Cassini infrared observations, and we find additional evidence for subsidence of enriched air onto Titan's south pole during this time period. Continued observations of Titan with ALMA beyond the summer solstice will enable further study of how Titan's atmospheric composition and dynamics respond to seasonal changes.

15 pages, 16 figures, 2 tables. Accepted for publication in Icarus, September 2018

References in corpus (12)

• Titan's Atmosphere and Climate
• Submillimeter Observations of Titan: Global Measures of Stratospheric Temperature, CO, HCN, HC3N, and the Isotopic Ratios 12C/13C and 14N/15N
• Detection of Propene in Titan's Stratosphere
• Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
• ALMA Observations of HCN and its Isotopologues on Titan
• ALMA measurements of the HNC and HC${}_3$N distributions in Titan's atmosphere
• Isotopic Ratios of Carbon and Oxygen in Titan's CO using ALMA
• Upper limits for undetected trace species in the stratosphere of Titan
• Seasonal evolution of ${\mathrm{C}}_2{\mathrm{N}}_2$, ${\mathrm{C}}_3{\mathrm{H}}_4$, and ${\mathrm{C}}_4{\mathrm{H}}_2$ abundances in Titan's lower stratosphere
• Spatial Variations in Titan's Atmospheric Temperature: ALMA and Cassini Comparisons from 2012 to 2015
• Interferometric imaging of Titan's HC${}_3$N, H${}^{13}$CCCN and HCCC${}^{15}$N
• Mapping Vinyl Cyanide and Other Nitriles in Titan's Atmosphere Using ALMA

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