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Spectral Line Survey Imaging of Titan’s Atmosphere with the SMA in 2019

Presentation #401.03 in the session Titan: Up High, Down Low.

Published onOct 20, 2022
Spectral Line Survey Imaging of Titan’s Atmosphere with the SMA in 2019

Ground-based observations of Titan in the millimeter/submillimeter bands have long been an important tool for understanding the physical and chemical characteristics of its stratosphere starting with the detection of upper atmospheric CO [1], nitriles [2-4], and isotopologues [5-6]). The development of the first mm-wave interferometers allowed for Titan to be coarsely resolved, providing crude maps and detection of winds [7-9]. In the past decade a sea change has come from the commissioning of ALMA, providing significant improvements in sensitivity and spatial resolution, leading to many detections of new species and novel isotopologues [10]. ALMA programs leading to highly resolved maps of many species, along with vertically resolved winds from 300 km into the thermosphere above 1000km, have now been presented [11-12].

We will present new spatially resolved observations of many nitriles in Titan’s stratosphere, obtained in 2019 as a spectral line survey using the Submillimeter Array (SMA). While significantly smaller than ALMA, the SMA provided 32 GHz of continuous bandwidth at 140 kHz resolution (roughly 34 times what ALMA can provide simultaneously at the same resolution), covering many different species and transitions. While the 2019 data have lower spatial resolution, many spectral lines were imaged by SMA and can be compared to the 2016 distributions mapped by ALMA. Most nitriles show significant changes in their distributions, following seasonal changes that have been explored by Cassini CIRS, for example [13-15]. Zonal wind estimates are also possible from the data. These measurements show that the SMA can play an important role going forward in measuring stratospheric seasonal variability. Current and future SMA upgrades will significantly improve upon the capabilities demostrated by these observations, and will allow for unique and timely measurements of Titan’s atmosphere in the coming years.

[1] Muhleman et al, Science 223, 393 (1984), [2] Paubert et al, BAAS 19, 633 (1987) [3] Bézard et al, 1992DPS 24.1201B (1992), [4] Bézard et al, 1993DPS 25.2509B (1993), [5] Hidayat et al, Icarus 126, 170 (1997), [6] Owen et al, IAU Circ. 7307 (1999), [7] Gurwell et al, 2004DPS 36.2016G (2004), [8] Moreno et al, A&A 437, 319 (2005), [9] Gurwell et al, 200DPS 41.3007G, [10] too many to list here! 1st Authors Nixon, Thelen, Palmer, Molter, Serigano, Lai, Garcia-Berrios and more. [11] Lellouch et al, Nature Astronomy 3, 614 (2019), [12] Cordiner et al, ApJ 904L12C (2020), [13] Flasar et al, 2004COSP 35, 534F (2004), [14] Teanby et al Icarus 181, 243T (2006) etc, [15] Vinatier et al, Icarus 188, 120V (2007) etc

Figure 1

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