Europlanet Science Congress 2022
Palacio de Congresos de Granada, Spain
18 – 23 September 2022
Europlanet Science Congress 2022
Palacio de Congresos de Granada, Spain
18 September – 23 September 2022
EPSC Abstracts
Vol. 16, EPSC2022-258, 2022
Europlanet Science Congress 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Isotopic ratios in Titan’s HCN and HC3N derived from Cassini/CIRS observations

Sandrine Vinatier1, Christophe Mathé1, Bruno Bézard1, Antoine Jolly2, and Thomas Gautier3
Sandrine Vinatier et al.
  • 1LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CNRS, Meudon, France (
  • 2LISA, CNRS, Université Paris-Est-Créteil, Université de Paris, Institut Pierre Simon Laplace, Créteil, France
  • 3LATMOS, CNRS, Sorbonne Université, Université Versailles St-Quentin, Guyancourt, France

Molecular nitrogen (N2) and methane (CH4) are the two major gas of Titan’s atmosphere. Their dissociation in the upper atmosphere by photons and photo-electrons leads to a wealth of chemical reactions forming more complex molecules like nitriles and hydrocarbons, which subsequently combine to form Titan’s photochemical haze.

Isotopic ratios measured in N2 and CH4 are of particular interest to constrain the origin and evolution of Titan’s atmosphere. While the same isotopic ratios measured in photochemical species bring constraints on fractionation processes occurring through their formation and/or loss.      

We focus on the determination on the 14N/15N and the 12C/13C isotopic ratios in HCN and the 12C/13C ratio in HC3N by analyzing their thermal emission acquired by the Cassini Composite Infrared Spectrometer (CIRS) from 2004 to 2017 (from the northern winter to the northern summer).  We used the entire CIRS dataset acquired with a limb-geometry viewing at the highest spectral resolution (0.5 cm-1). This allows us to search for potential variations of these isotopic ratios with latitude or with season, which could help to identify potential fractionation processes. Our analysis incorporates the temperature and minor species volume mixing ratio profiles inferred previously by Mathé et al. (2020) from the same limb dataset. We will present our results regarding the isotopic ratios in HCN for all latitudes, while we will present the 12C/13C ratio in HC3N only at high latitudes, as this nitrile is not detected at mid- and low-latitudes.

- Mathé et al., 2020. Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017. Icarus 344,  id. 113547.


How to cite: Vinatier, S., Mathé, C., Bézard, B., Jolly, A., and Gautier, T.: Isotopic ratios in Titan’s HCN and HC3N derived from Cassini/CIRS observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-258,, 2022.

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