# Ground-based monitoring and search for new species in Titan's atmosphere with TEXES

Athena Coustenis, Conor Nixon, Therese Encrenaz, Thomas Greathouse, D. Jacquemart, P. Lavvas, Rohini S. Giles, Nicolas Lombardo, Pascale Soulard, Lahouari Krim, et al.

► To cite this version:

Athena Coustenis, Conor Nixon, Therese Encrenaz, Thomas Greathouse, D. Jacquemart, et al. Ground-based monitoring and search for new species in Titan's atmosphere with TEXES. AAS Division for Planetary Sciences meeting #56, Oct 2025, Boise ID, United States. hal-05369075

HAL Id: hal-05369075

https://hal.science/hal-05369075v1

Submitted on 26 Nov 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
The full degree of Titan's organic chemistry complexity is not yet fully understood (e.g. Coustenis, 2021; Nixon, 2024). Several hydrocarbons and nitriles have already been detected in the atmosphere and their seasonal variations studied with Cassini/CIRS. Other minor species have been detected from the ground mainly in the millimeter range or by space-borne observatories like ISO (Coustenis et al., 1998). These results have been included in photochemical models (Lavvas et al. 2008, and this work) that have also predicted the presence of other minor species. In 2022 we did an observing campaign using the TEXES imaging spectrometer at the IRTF to monitor the infrared signatures of HCN and HC3N, along with acetylene (C2H2 and C2HD). In addition, we have been searching for cyanopropyne (C4H3N) and isobutyronitrile (C4H7N) in the 20-micron region. High-resolution spectra of Titan have been obtained in September 2022 in: (1) 498-500 cm-1 (C2HD, HC3N, search for C4H3N); (2) 537-540 cm-1 (C2HD, search for C4H7N); (3) 744-749 cm-1 (C2H2, HCN); (4) 1244-1250 cm-1 (CH4). Data are under processing (Coustenis et al., 2023). In 2023, laboratory spectra of cyanopropyne and isobutyronitrile have been recorded by our team in the 495-505 cm-1 and 510-570 cm-1 spectral ranges, respectively, with a spectral resolution of 0.01 cm-1 and 0.056 cm-1 (Jacquemart et al., in prep.). Cross sections have been derived for these two molecules and upper limits will be derived. TEXES data will also be used for a study of the variations of HCN and HC3N after the end of the Cassini mission, and for a retrieval of D/H. We also plan to use the TEXES instrument in conjunction with other larger telescopes in order to optimize the search range and to acquire detection or upper limits for some of these new molecules. We are also exploring Cassini/CIRS data to check for possible new detections or for establishing an upper limit to some of the nitriles.

References

Coustenis, A., et al., 1998. Evidence for water vapor in Titan's atmosphere from ISO/SWS data. Astron. Astrophys. 336, L85-L89

Coustenis, A., 2021. "The Atmosphere of Titan". In Read, P. (Ed.), Oxford Research Encyclopedia of Planetary Science. Oxford University Press.

Coustenis, A., et al., 2023. Titan's chemical composition from Cassini and ground-based measurements. IUGG 2023, Berlin, Germany, 11-20 July.

Lavvas, P., Coustenis, A., Vardavas, I. M., 2008. Coupling photochemistry with haze formation in Titan's atmosphere. Part I: Model description. Plan. Space Sci. 56, 27-66.

Nixon, C. A., 2024. The Composition and Chemistry of Titan's Atmosphere. ACS Earth and Space Chemistry 2024 8 (3), 406-456.