Seasonal Evolution of Titan's Stratosphere Near the Poles

• Published in: The Astrophysical Journal
• Main Authors: Coustenis, A., Jennings, D., Achterberg, R., Bampasidis, G., Nixon, C., Lavvas, Panayotis, Cottini, V., Flasar, F. M.
• Other Authors: Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), NASA Goddard Space Flight Center (GSFC), National and Kapodistrian University of Athens (NKUA), Groupe de spectrométrie moléculaire et atmosphérique (GSMA), Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), University of Maryland Baltimore County (UMBC), University of Maryland System
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: infrared: planetary systems; planets and satellites: atmospheres; planets and satellites: composition; planets and satellites: individual (Titan); radiation mechanisms: thermal; radiative transfer; [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]; South pole
• Online Access: https://hal.sorbonne-universite.fr/hal-01826240; https://hal.sorbonne-universite.fr/hal-01826240/document; https://hal.sorbonne-universite.fr/hal-01826240/file/Coustenis_2018_ApJL_854_L30_sans%20marque.pdf; https://doi.org/10.3847/2041-8213/aaadbd

International audience In this Letter, we report the monitoring of seasonal evolution near Titan's poles. We find Titan's south pole to exhibit since 2010 a strong temperature decrease and a dramatic enhancement of several trace species such as complex hydrocarbons and nitriles (HC 3 N and C 6 H 6 in particular) previously only observed at high northern latitudes. This results from the seasonal change on Titan going from winter (2002) to summer (2017) in the north and, at the same time, the onset of winter in the south pole. During this transition period atmospheric components with longer chemical lifetimes linger in the north, undergoing slow photochemical destruction, while those with shorter lifetimes decrease and reappear in the south. An opposite effect was expected in the north, but not observed with certainty until now. We present here an analysis of high-resolution nadir spectra acquired by Cassini/Cassini Composite Infrared Spectrometer in the past years and describe the temperature and composition variations near Titan's poles. From 2013 until 2016, the northern polar region has shown a temperature increase of 10 K, while the south has shown a more significant decrease (up to 25 K) in a similar period of time. While the south polar region has been continuously enhanced since about 2012, the chemical content in the north is finally showing a clear depletion for most molecules only since 2015. This is indicative of a non-symmetrical response to the seasons in Titan's stratosphere that can set constraints on photochemical and GCM models.