Mapping Vinyl Cyanide and Other Nitriles in Titan’s Atmosphere Using ALMA

Journal Article · Wed Nov 01 04:00:00 EDT 2017 · Astronomical Journal (Online)

DOI:https://doi.org/10.3847/1538-3881/AA8EEF· OSTI ID:22663118

Cordiner, M. A.; Nixon, C. A.; Achterberg, R. K.; Molter, E. M.; Palmer, M. Y.; Charnley, S. B.; Lindberg, J. E.; Mumma, M. J. ^[1]; Teanby, N. A. ^[2]; Kisiel, Z. ^[3]; Irwin, P. G. J., ^[4]

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1. NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
2. School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ (United Kingdom)
3. Institute of Physics, Polish Academy of Sciences, Al. Lotnikøw 32/46, 02-668 Warszawa (Poland)
4. Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom)

Vinyl cyanide (C{sub 2}H{sub 3}CN) is theorized to form in Titan’s atmosphere via high-altitude photochemistry and is of interest regarding the astrobiology of cold planetary surfaces due to its predicted ability to form cell membrane-like structures (azotosomes) in liquid methane. In this work, we follow up on the initial spectroscopic detection of C{sub 2}H{sub 3}CN on Titan by Palmer et al. with the detection of three new C{sub 2}H{sub 3}CN rotational emission lines at submillimeter frequencies. These new, high-resolution detections have allowed for the first spatial distribution mapping of C{sub 2}H{sub 3}CN on Titan. We present simultaneous observations of C{sub 2}H{sub 5}CN, HC{sub 3}N, and CH{sub 3}CN emission, and obtain the first (tentative) detection of C{sub 3}H{sub 8} (propane) at radio wavelengths. We present disk-averaged vertical abundance profiles, two-dimensional spatial maps, and latitudinal flux profiles for the observed nitriles. Similarly to HC{sub 3}N and C{sub 2}H{sub 5}CN, which are theorized to be short-lived in Titan’s atmosphere, C{sub 2}H{sub 3}CN is most abundant over the southern (winter) pole, whereas the longer-lived CH{sub 3}CN is more concentrated in the north. This abundance pattern is consistent with the combined effects of high-altitude photochemical production, poleward advection, and the subsequent reversal of Titan’s atmospheric circulation system following the recent transition from northern to southern winter. We confirm that C{sub 2}H{sub 3}CN and C{sub 2}H{sub 5}CN are most abundant at altitudes above 200 km. Using a 300 km step model, the average abundance of C{sub 2}H{sub 3}CN is found to be 3.03 ± 0.29 ppb, with a C{sub 2}H{sub 5}CN/C{sub 2}H{sub 3}CN abundance ratio of 2.43 ± 0.26. Our HC{sub 3}N and CH{sub 3}CN spectra can be accurately modeled using abundance gradients above the tropopause, with fractional scale-heights of 2.05 ± 0.16 and 1.63 ± 0.02, respectively.

• OSTI ID: 22663118
• Journal Information: Astronomical Journal (Online), Journal Name: Astronomical Journal (Online) Journal Issue: 5 Vol. 154; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTROSCOPY
ACETONITRILE
ACRYLONITRILE
ADVECTION
ALTITUDE
ASTRONOMY
ATMOSPHERIC CIRCULATION
DETECTION
MAPPING
METHANE
PHOTOCHEMISTRY
PLANETS
PROPANE
SATELLITE ATMOSPHERES
SATELLITES
SCALE HEIGHT
TROPOPAUSE
TWO-DIMENSIONAL CALCULATIONS