Methane emission from a cool brown dwarf

Jacqueline K Faherty; Ben Burningham; Jonathan Gagné; Genaro Suárez; Johanna M Vos; Sherelyn Alejandro Merchan; Caroline V Morley; Melanie Rowland; Brianna Lacy; Rocio Kiman; Dan Caselden; J Davy Kirkpatrick; Aaron Meisner; Adam C Schneider; Marc Jason Kuchner; Daniella Carolina Bardalez Gagliuffi; Charles Beichman; Peter Eisenhardt; Christopher R Gelino; Ehsan Gharib-Nezhad; Eileen Gonzales; Federico Marocco; Austin James Rothermich; Niall Whiteford

doi:10.1038/s41586-024-07190-w

Methane emission from a cool brown dwarf

Nature. 2024 Apr;628(8008):511-514. doi: 10.1038/s41586-024-07190-w. Epub 2024 Apr 17.

Authors

Jacqueline K Faherty^{1

2}, Ben Burningham³, Jonathan Gagné^{4

5}, Genaro Suárez⁶, Johanna M Vos^{6

7}, Sherelyn Alejandro Merchan^{6

8}, Caroline V Morley⁹, Melanie Rowland⁹, Brianna Lacy⁹, Rocio Kiman¹⁰, Dan Caselden⁶, J Davy Kirkpatrick¹¹, Aaron Meisner¹², Adam C Schneider¹³, Marc Jason Kuchner¹⁴, Daniella Carolina Bardalez Gagliuffi^{6

15}, Charles Beichman¹¹, Peter Eisenhardt¹⁶, Christopher R Gelino¹¹, Ehsan Gharib-Nezhad¹⁷, Eileen Gonzales^{18

19}, Federico Marocco¹¹, Austin James Rothermich^{6

20}, Niall Whiteford⁶

Affiliations

¹ Department of Astrophysics, American Museum of Natural History, New York, NY, USA. jfaherty@amnh.org.
² Department of Physics, The Graduate Center City University of New York, New York, NY, USA. jfaherty@amnh.org.
³ Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, UK.
⁴ Planétarium Rio Tinto Alcan, Montreal, Quebec, Canada.
⁵ Département de Physique, Université de Montréal, Montreal, Quebec, Canada.
⁶ Department of Astrophysics, American Museum of Natural History, New York, NY, USA.
⁷ School of Physics, Trinity College Dublin, The University of Dublin, Dublin, Ireland.
⁸ Department of Physics & Astronomy, Hunter College, New York, NY, USA.
⁹ Department of Astronomy, University of Texas at Austin, Austin, TX, USA.
¹⁰ Department of Astronomy, California Institute of Technology, Pasadena, CA, USA.
¹¹ IPAC, Caltech, Pasadena, CA, USA.
¹² NSF's National Optical-Infrared Astronomy Research Laboratory, Tucson, AZ, USA.
¹³ United States Naval Observatory, Flagstaff, AZ, USA.
¹⁴ Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
¹⁵ Department of Physics & Astronomy, Amherst College, Amherst, MA, USA.
¹⁶ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
¹⁷ NASA Ames Research Center, Mountain View, CA, USA.
¹⁸ Department of Physics, San Francisco State University, San Francisco, CA, USA.
¹⁹ Department of Astronomy and Carl Sagan Institute, Cornell University, Ithaca, NY, USA.
²⁰ Department of Physics, The Graduate Center City University of New York, New York, NY, USA.

Abstract

Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs^1,2. Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H₃⁺ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported³. CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482 K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326 μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300 K centred at 1-10 mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H₃⁺ emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H₃⁺ at the higher pressure where the W1935 emission originates⁴.