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A study of very high resolution visible spectra of Titan: Line characterisation in visible CH4 bands and the search for C3

R Rianço-Silva, P. Machado, Z. Martins, E. Lellouch, J. Loison, M. Dobrijévic, J. A Dias, J. Ribeiro

The atmosphere of Titan is a unique natural laboratory for the study of atmospheric evolution and photochemistry akin to that of the primitive Earth, with a wide array of complex molecules discovered through infrared and sub-mm spectroscopy. Here, we explore high resolution visible spectra of Titan (obtained with VLT-UVES) and retrieve an empirical high resolution list of methane absorption features at high resolution, (R=100 000) between 5250 Å and 6180 Å, for which no linelists are yet available. Furthermore, we search for the predicted, but previously undetected carbon trimer, C3, on the atmosphere of Titan, at its 4051 Å band. Our results are consistent with the presence of C3 at the upper atmosphere of Titan, with a column density of 1013 cm-2. This study of Titan’s atmosphere with high-resolution visible spectroscopy presents a unique opportunity to observe a planetary atmosphere where CH4 is the main visible molecular absorber, from which CH4 optical proprieties can be studied. It also showcases the use of a close planetary target to test new methods for chemical retrieval of minor atmospheric compounds, in preparation for upcoming studies of cold terrestrial exoplanet atmospheres.

TitanHigh resolution visible spectroscopyMinor chemical speciesMethaneChemical retrieval of planetary atmospheresPhotochemistryC3

Planetary and Space Science
Volume 240
2024 January

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia