The JWST Early-release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 μm Spectrum of the Planetary-mass Companion VHS 1256–1257 b
Authors: Miles Brittany E. , Biller Beth A. , Patapis Polychronis , Worthen Kadin , Rickman Emily , Hoch Kielan K. W. , Skemer Andrew , Perrin Marshall D. , Whiteford Niall , Chen Christine H. , Sargent B. , Mukherjee Sagnick , Morley Caroline V. , Moran Sarah E. , Bonnefoy Mickael , Petrus Simon , Carter Aarynn L. , Choquet Elodie , Hinkley Sasha , Ward-Duong Kimberly , Leisenring Jarron M. , Millar-Blanchaer Maxwell A. , Pueyo Laurent , Ray Shrishmoy , Sallum Steph , Stapelfeldt Karl R. , Stone Jordan M. , Wang Jason J. , Absil Olivier , Balmer William O. , Boccaletti Anthony , Bonavita Mariangela , Booth Mark , Bowler Brendan P. , Chauvin Gael , Christiaens Valentin , Currie Thayne , Danielski Camilla , Fortney Jonathan J. , Girard Julien H. , Grady Carol A. , Greenbaum Alexandra Z. , Henning Thomas , Hines Dean C. , Janson Markus , Kalas Paul , Kammerer Jens , Kennedy Grant M. , Kenworthy Matthew A. , Kervella Pierre , Lagage Pierre-Olivier , Lew Ben W. P. , Liu Michael C. , Macintosh Bruce , Marino Sebastian , Marley Mark S. , Marois Christian , Matthews Elisabeth C. , Matthews Brenda C. , Mawet Dimitri , McElwain Michael W. , Metchev Stanimir , Meyer Michael R. , Molliere Paul , Pantin Eric , Quirrenbach Andreas , Rebollido Isabel , Ren Bin B. , Schneider Glenn , Vasist Malavika , Wyatt Mark C. , Zhou Yifan , Briesemeister Zackery W. , Bryan Marta L. , Calissendorff Per , Cantalloube Faustine , Cugno Gabriele , De Furio Matthew , Dupuy Trent J. , Factor Samuel M. , Faherty Jacqueline K. , Fitzgerald Michael P. , Franson Kyle , Gonzales Eileen C. , Hood Callie E. , Howe Alex R. , Kraus Adam L. , Kuzuhara Masayuki , Lagrange Anne-Marie , Lawson Kellen , Lazzoni Cecilia , Liu Pengyu , Llop-Sayson Jorge , Lloyd James P. , Martinez Raquel A. , Mazoyer Johan , Quanz Sascha P. , Redai Jea Adams , Samland Matthias , Schlieder Joshua E. , Tamura Motohide , Tan Xianyu , Uyama Taichi , Vigan Arthur , Vos Johanna M. , Wagner Kevin , Wolff Schuyler G. , Ygouf Marie , Zhang Xi , Zhang Keming , Zhang Zhoujian 
Published: March 2023

Abstract
We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a <20 M
Jup widely separated (∼8″, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20 μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.