The atmosphere of Titan in late northern summer from JWST and Keck observations

Creators: Nixon, Conor A.¹; Bézard, Bruno²; Cornet, Thomas³; Coy, Brandon Park⁴; de Pater, Imke⁵; Es-Sayeh, Maël^{2, 6, 7}; Hammel, Heidi B.⁸; Lellouch, Emmanuel²; Lombardo, Nicholas A.⁹; López-Puertas, Manuel¹⁰; Lora, Juan M.⁹; Rannou, Pascal¹¹; Rodriguez, Sébastien^{2, 6}; Teanby, Nicholas A.¹²; Turtle, Elizabeth P.¹³; Achterberg, Richard K.¹⁴; Alvarez, Carlos¹⁵; Davies, Ashley G.¹⁶; de Kleer, Katherine¹⁷; Doppmann, Greg¹⁵; Fletcher, Leigh N.¹⁸; Hayes, Alexander G.¹⁹; Holler, Bryan J.²⁰; Irwin, Patrick G. J.²¹; Jordan, Carolyn¹⁵; King, Oliver R. T.¹⁸; Kutsop, Nicholas W.²²; Marlin, Theresa C.¹⁷; Melin, Henrik²³; Milam, Stefanie N.¹; Molter, Edward M.²⁰; Moore, Luke²⁴; Nyffenegger-Péré, Yaniss¹⁰; O'Donoghue, James²⁵; O'Meara, John¹⁵; Rafkin, Scot C. R.²⁶; Roman, Michael T.¹⁸; Rostopchina, Arina¹⁵; Rowe-Gurney, Naomi²⁵; Schmidt, Carl¹; Schmidt, Judy²⁷; Sotin, Christophe²⁸; Stallard, Tom S.²³; Stansberry, John A.²⁰; West, Robert A.¹⁶

1. Goddard Space Flight Center
2. University of Paris
3. European Space Astronomy Centre
4. University of Chicago
5. University of California, Berkeley
6. Institut de Physique du Globe de Paris
7. Centre National de Recherches Météorologiques
8. Association of Universities For Research In Astronomy
9. Yale University
10. Instituto de Astrofísica de Andalucía
11. Molecular and Atmospheric Spectrometry Group
12. University of Bristol
13. Johns Hopkins University Applied Physics Laboratory
14. University of Maryland, College Park
15. W.M. Keck Observatory
16. Jet Propulsion Lab
17. California Institute of Technology
18. University of Leicester
19. Cornell University
20. Space Telescope Science Institute
21. University of Oxford
22. University of Idaho
23. Northumbria University
24. Boston University
25. University of Reading
26. Southwest Research Institute
27. Independent Astronomer, San Francisco, CA, USA
28. Laboratoire de Planétologie et Géodynamique de Nantes

Abstract

Saturn's moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan's northern winter and spring were investigated in detail by the Cassini–Huygens spacecraft (2004–2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan's late northern summer. Using JWST's mid-infrared instrument, we spectroscopically detected the methyl radical, the primary product of methane break-up and key to the formation of ethane and heavier molecules. Using the near-infrared spectrograph onboard JWST, we detected several non-local thermodynamic equilibrium CO and CO2 emission bands, which allowed us to measure these species over a wide altitude range. Lastly, using the near-infrared camera onboard JWST and Keck II, we imaged northern hemisphere tropospheric clouds evolving in altitude, which provided new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modelling of Titan's climate and meteorology as it progresses through the northern fall equinox, when its atmosphere is expected to show notable seasonal changes.

Copyright and License

Acknowledgement

C.A.N. was funded for this work by JWST Archive Research Project 02524. B.B., E.L., P.R., S.R. and M.E.-S. acknowledge support from the Programme National de Planétologie of CNRS-INSU co-funded by CNES. S.R. also acknowledges financial support from the CNES and the French National Research Agency (grant nos. ANR-21-CE49-0020-04/RAD³-NET and ANR-23-CE56-0008/EOLE). M.L.-P. acknowledges financial support from the Agencia Estatal de Investigación, MCIN/AEI/10.13039/501100011033 (grant nos. PID2022-141216NB-I00 and CEX2021-001131-S). N.A.T. was funded by the UK Science and Technology Facilities Council (grant no. ST/Y000676/1). N.A.L. and J.M.L. were funded by NASA CDAP (grant no. 80NSSC20K0483). H.B.H. and S.N.M. acknowledge support from NASA JWST Interdisciplinary Scientist grant 21-SMDSS21-0013. H.M. was supported by the STFC James Webb Fellowship (ST/W001527/2) at Northumbria University. LNF, ORTK and MTR were supported by STFC Consolidated Grant reference ST/W00089X/1. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to the Author Accepted Manuscript version arising from this submission. A portion of this work used the ALICE high performance computing facility at the University of Leicester. This work is based in part on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programme 1251. We thank the following staff at the Space Telescope Institute for support with the execution of the JWST observations: K. Murray, B. Hilbert, G. Wahlgren and B. Porterfield. Some of the data presented in this paper were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. Observing time for this project was allocated by all three institutions, in part thanks to the Twilight Zone Program. NASA Keck time is administered by the NASA Exoplanet Science Institute. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We recognize and acknowledge the important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have had the opportunity to conduct observations from this mountain.

Data Availability

JWST observational data are accessible from the Barbara A. Mikulski Archive for Space Telescopes (https://mast.stsci.edu). All Keck data, including the Twilight Zone data, are made public after 18 months, and can be retrieved from the Keck Observatory Archive (https://koa.ipac.caltech.edu/UserGuide/about.html).

Code Availability

The custom pipeline and data processing code¹⁰⁴ used in this study is available from https://doi.org/10.3847/2515-5172/ad045f. NIRC2 distortion files and IDL software to correct the images for distortion can be downloaded from https://www2.keck.hawaii.edu/inst/nirc2/dewarp.html. General software to reduce Keck NIRC2 (Twilight Zone) data can be obtained from https://nirc2-reduce.readthedocs.io/en/latest/. The NEMESIS modelling software used for MIRI analysis is fully described in ref. ⁶⁰ and available from GitHub (https://github.com/nemesiscode/radtrancode). The radiative transfer code used to generate the NIRSpec LTE spectra is available from B.B. upon reasonable request. The KOPRA radiative transfer code and the GRANADA non-LTE code used in the analysis of the CO₂ and CO emissions are available from M.L.-P. upon request.

Supplemental Material

Supplementary Information

Data processing details, Figs. 1–4 and Tables 1–5.

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