Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
EPSC Abstracts
Vol. 14, EPSC2020-380, 2020, updated on 14 May 2022
https://doi.org/10.5194/epsc2020-380
Europlanet Science Congress 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Detection of Cyclopropenylidene on Titan

Conor Nixon1, Alexander Thelen1,2, Martin Cordiner1,3, Zbigniew Kisiel4, Steven Charnley1, Edward Molter5, Joseph Serigano6, Patrick Irwin7, Nicholas Teanby8, and Yi-Jehng Kuan9,10
Conor Nixon et al.
  • 1Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, United States of America (conor.a.nixon@nasa.gov)
  • 2Universities Space Research Association, Columbia, MD 21046, USA
  • 3Department of Physics, Catholic University of America, Washington, DC 20064, USA
  • 4Institute of Physics, Polish Academy of Sciences, Al. Lotnik_ow 32/46, 02-668 Warszawa, Poland
  • 5Department of Astronomy, University of California, Berkeley, CA 94720, USA
  • 6Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA
  • 7Atmospheric, Oceanic, and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU, UK
  • 8School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK
  • 9Department of Earth Sciences, National Taiwan Normal University, Taipei 116, Taiwan, ROC
  • 10Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan, ROC

Titan, Saturn’s largest moon, has long been known to harbor a thick atmosphere [1] that evolves a complex array of organic molecules through atmospheric photochemistry [2, 3]. Especially from the 1970s onwards, successive waves of investigation with ground-based telescopes, spacecraft including Voyager 1 and Cassini-Huygens, and space telescopes have revealed the molecular inventory of its atmosphere through remote sensing at UV to radio wavelengths, and in situ mass spectroscopy [4, 5]. Since coming online in 2012, the ALMA (Atacama Large Millimeter/submillimeter Array) telescope has added importantly to our knowledge of Titan’s atmospheric composition, especially through first detections of propionitrile (ethyl cyanide, C2H5CN) and acrylonitrile (vinyl cyanide, C2H3CN) in the neutral atmosphere [6, 7]. Such new measurements are of vital importance for constraining photochemical models [8-10] and helping us unravel the steps to building even larger molecules and haze particles [11], with important repercussions for astrobiology [12].

In recent years we have continued the search for new molecules in Titan’s atmosphere, acquiring high-sensitivity observations with ALMA to search for larger hydrocarbons, nitriles and other species. In 2016 we acquired 129 mins of integration on Titan in ALMA Band 6 that exhibited many lines of C2H5CN (ethyl cyanide) and other known species. In addition we found several weak lines that we identified as c-C3H2 (cyclopropenylidene), a small cyclic molecule frequently seen in the interstellar medium [13, 14], but not previously seen in a planetary atmosphere. The spectrum was modeled using the NEMESIS radiative transfer and inversion computer model [15] yielding a best-fit mixing column abundance of 5.29x1012 molecule cm-2, somewhat greater than predicted by recent photochemical models (1.41x1012 [8]; 7.71x1011 [16]).

Cyclopropenylidene is now only the second cyclic molecule to be detected in a planetary atmosphere after benzene. Its measurement will provide vital constraints on the chemistry of important intermediate-size radicals such as C3H3 (propargyl and its isomers) whose chemistry may lead to either c-C3H2 (by hydrogen loss) or to benzene (e.g. by self-reaction). Ultimately, a better understanding of cyclic molecule chemistry will lead to a better understanding of haze formation, and Titan’s potential for astrobiology. 

References

[1]       G. P. Kuiper, "Titan: A satellite with an atmosphere," Astrophysical Journal, vol. 100, no. 3, pp. 378-383, Nov 1944, doi: 10.1086/144679.

[2]       Y. L. Yung, M. Allen, and J. P. Pinto, "Photochemistry of the Atmosphere of Titan - Comparison Between Model and Observations," Astrophysical Journal Supplement Series, vol. 55, no. 3, pp. 465-506, 1984, doi: 10.1086/190963.

[3]       Y. L. Yung, "An Update of Nitrile Photochemistry on Titan," Icarus, vol. 72, no. 2, pp. 468-472, Nov 1987, doi: 10.1016/0019-1035(87)90186-2.

[4]       B. Bezard, R. V. Yelle, and C. A. Nixon, "The composition of Titan's atmosphere," (in English), Titan: Interior, Surface, Atmosphere, and Space Environment, Article; Book Chapter no. 14, pp. 158-189, 2014.

[5]       S. M. Horst, "Titan's atmosphere and climate," Journal of Geophysical Research-Planets, vol. 122, no. 3, pp. 432-482, Mar 2017, doi: 10.1002/2016je005240.

[6]       M. A. Cordiner et al., "ETHYL CYANIDE ON TITAN: SPECTROSCOPIC DETECTION AND MAPPING USING ALMA," Astrophysical Journal Letters, vol. 800, no. 1, Feb 10 2015, Art no. L14, doi: 10.1088/2041-8205/800/1/l14.

[7]       M. Y. Palmer et al., "ALMA detection and astrobiological potential of vinyl cyanide on Titan," Science Advances, vol. 3, no. 7, Jul 2017, Art no. e1700022, doi: 10.1126/sciadv.1700022.

[8]       V. Vuitton, R. V. Yelle, S. J. Klippenstein, S. M. Horst, and P. Lavvas, "Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model," Icarus, vol. 324, pp. 120-197, May 2019, doi: 10.1016/j.icarus.2018.06.013.

[9]       K. Willacy, M. Allen, and Y. Yung, "A NEW ASTROBIOLOGICAL MODEL OF THE ATMOSPHERE OF TITAN," Astrophysical Journal, vol. 829, no. 2, Oct 2016, Art no. 79, doi: 10.3847/0004-637x/829/2/79.

[10]     J. C. Loison et al., "The neutral photochemistry of nitriles, amines and imines in the atmosphere of Titan," Icarus, vol. 247, pp. 218-247, Feb 2015, doi: 10.1016/j.icarus.2014.09.039.

[11]     J. C. Loison, M. Dobrijevic, and K. M. Hickson, "The photochemical production of aromatics in the atmosphere of Titan," Icarus, vol. 329, pp. 55-71, Sep 2019, doi: 10.1016/j.icarus.2019.03.024.

[12]     S. M. Horst et al., "Formation of Amino Acids and Nucleotide Bases in a Titan Atmosphere Simulation Experiment," Astrobiology, vol. 12, no. 9, pp. 809-817, Sep 2012, doi: 10.1089/ast.2011.0623.

[13]     P. Thaddeus, J. M. Vrtilek, and C. A. Gottlieb, "LABORATORY AND ASTRONOMICAL IDENTIFICATION OF CYCLOPROPENYLIDENE, C3H2," Astrophysical Journal, vol. 299, no. 1, pp. L63-L66, Dec 1985, doi: 10.1086/184581.

[14]     D. Fosse, J. Cernicharo, M. Gerin, and P. Cox, "Molecular carbon chains and rings in TMC-1," Astrophysical Journal, vol. 552, no. 1, pp. 168-174, May 2001, doi: 10.1086/320471.

[15]     P. G. J. Irwin et al., "The NEMESIS planetary atmosphere radiative transfer and retrieval tool," Journal of Quantitative Spectroscopy & Radiative Transfer, vol. 109, no. 6, pp. 1136-1150, Apr 2008, doi: 10.1016/j.jqsrt.2007.11.006.

[16]     E. Hebrard, M. Dobrijevic, J. C. Loison, A. Bergeat, K. M. Hickson, and F. Caralp, "Photochemistry of C3Hp hydrocarbons in Titan's stratosphere revisited," Astronomy & Astrophysics, vol. 552, Apr 2013, Art no. A132, doi: 10.1051/0004-6361/201220686.

How to cite: Nixon, C., Thelen, A., Cordiner, M., Kisiel, Z., Charnley, S., Molter, E., Serigano, J., Irwin, P., Teanby, N., and Kuan, Y.-J.: Detection of Cyclopropenylidene on Titan, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-380, https://doi.org/10.5194/epsc2020-380, 2020.