# Ground-based monitoring of atmospheric species on Titan and a search for new nitriles with IRTF/TEXES

Athena Coustenis, Therese Encrenaz, Thomas Greathouse, David Jacquemart, Conor Nixon, Panayotis Lavvas, Rohini Giles, Nicholas Lombardo, Bruno Bezard, Krim Lahouari, et al.

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

To cite this version:

Athena Coustenis, Therese Encrenaz, Thomas Greathouse, David Jacquemart, Conor Nixon, et al. Ground-based monitoring of atmospheric species on Titan and a search for new nitriles with IRTF/TEXES. Europlanet Science Congress 2024, Sep 2024, Berlin, Germany. 10.5194/epsc2024-96. hal-04774719

HAL Id: hal-04774719

https://hal.science/hal-04774719v1

Submitted on 28 Nov 2024

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_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

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

**Athena Coustenis**<fnref n="1" />, **Therese Encrenaz**<fnref n="1" />, **Thomas K. Greathouse**<fnref n="2" />, **David Jacquemart**<fnref n="3" />, **Conor Nixon**<fnref n="4" />, **Panayotis Lavvas**<fnref n="5" />, **Rohini Giles**<fnref n="6" />, **Nicholas Lombardo**<fnref n="7" />, **Bruno Bezard**<fnref n="1" />, **Krim Lahouari**<fnref n="3" />, **Pascale Soulard**<fnref n="3" />, **Benoit Tremblay**<fnref n="3" />, **Sandrine Vinatier**<fnref n="1" />, **Antoine Jolly**<fnref n="8" />, and **Brendan Steffens**<fnref n="9" />

Titan's organic chemistry has been partly revealed from Cassini-Huygens and recent ground-based observations so far, but the full degree of its 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 in particular by the CIRS instrument aboard Cassini. Other minor species have been detected from the ground mainly in the millimeter range or space-borne observatories like ISO (Coustenis et al., 1998). These results have been included in photochemically models (Lavvas et al. 2008, and this work) that have also predicted the presence of other minor species, among which some have infrared transitions in the 5-25-mm spectral range, where propane (C₃H₈) and allene (CH₂CCH₂) have already been detected. We have started an observing campaign using the TEXES thermal infrared imaging spectrometer at the Infrared Telescope Facility (Mauna Kea Observatory) to monitor the infrared signatures of hydrogen cyanide (HCN) and cyanoacetylene (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 the following spectral ranges: (1) 498-500 cm⁻<fnref n="1" /> (C₂HD, HC₃N, search for C₄H₃N); (2) 537-540 cm⁻<fnref n="1" /> (C₂HD, search for C₄H₇N); (3) 744-749 cm⁻<fnref n="1" /> (C₂H₂, HCN); (4) 1244-1250 cm⁻<fnref n="1" /> (CH₄). Data are presently under reduction and preliminary results presented (Coustenis et al., 2023). In 2023, laboratory spectra of cyanopropyne and isobutyronitrile have been recorded in the 495-505 cm⁻<fnref n="1" /> and 510-570 cm⁻<fnref n="1" /> spectral ranges, respectively, with a spectral resolution of 0.01 cm⁻<fnref n="1" /> and 0.056 cm⁻<fnref n="1" /> by our team (Jacquemart et al., in preparation). Cross sections have been derived for these two molecules and upper limits will be derived for these two molecules in the atmosphere of Titan. TEXES data will also be used for a study of the variations of HCN and HC₃N since the end of the Cassini mission, and for a retrieval of D/H from C₂HD/C₂H₂. We now 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

<footnote n="1">¹Paris Observatory, CNRS, PSL Univ., LESIA, Meudon, France (athena.coustenis@obspm.fr)</footnote>

<footnote n="2">²Southwest Research Institute, San Antonio, TX 78232, USA</footnote>

<footnote n="3">³MONARIS, Sorbonne Université, CNRS, 75005 Paris, France</footnote>

<footnote n="4">⁴Planetary Systems Lab., NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA</footnote>

<footnote n="5">⁵GSMA, Université Reims Champagne Ardenne (URCA), Reims, France</footnote>

<footnote n="6">⁶SWRI, Southwest Research Institute, Boulder, CO 80302 USA</footnote>

<footnote n="7">⁷Dept of Earth and Planetary Sciences, Yale Univ., New Haven, CT, USA</footnote>

<footnote n="8">⁸LISA, Univ. Paris XII—Val de Marne et Paris VII, 94010 Créteil Cx, France</footnote>

<footnote n="9">⁹Max Planck Inst. for Chemistry, Hahn-Meitner-Weg 1, Mainz, 55128, Germany</footnote>
or for establishing an upper limit to some of the nitriles.

## References

* Coustenis, A., 2021. "The Atmosphere of Titan". In Read, P. (Ed.), *Oxford Research Encyclopedia of Planetary Science*. Oxford University Press. doi:https://doi.org/10.1093/acrefore/9780190647926.013.120

* Nixon, C. A., 2024. The Composition and Chemistry of Titan's Atmosphere. *ACS Earth and Space Chemistry* 2024 8 (3), 406-456. DOI: 10.1021/acsearthspacechem.2c00041

* Coustenis, A., Salama, A., Lellouch, E., Encrenaz, Th., Bjoraker, G., Samuelson, R. E., de Graauw, Th., Feuchtgruber, H., Kessler, M. F., 1998. Evidence for water vapor in Titan's atmosphere from ISO/SWS data. *Astron. Astrophys.* 336, L85-L89.

* 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.

* Coustenis, A., Nixon, C. A., Encrenaz, Th., Lavvas, P., 2023. Titan's chemical composition from Cassini and ground-based measurements. *IUGG 2023, Berlin, Germany, 11-20 July.*