The Astrophysical Journal Letters (Jan 2024)
JWST/NIRISS Reveals the Water-rich “Steam World” Atmosphere of GJ 9827 d
- Caroline Piaulet-Ghorayeb,
- Björn Benneke,
- Michael Radica,
- Eshan Raul,
- Louis-Philippe Coulombe,
- Eva-Maria Ahrer,
- Daria Kubyshkina,
- Ward S. Howard,
- Joshua Krissansen-Totton,
- Ryan J. MacDonald,
- Pierre-Alexis Roy,
- Amy Louca,
- Duncan Christie,
- Marylou Fournier-Tondreau,
- Romain Allart,
- Yamila Miguel,
- Hilke E. Schlichting,
- Luis Welbanks,
- Charles Cadieux,
- Caroline Dorn,
- Thomas M. Evans-Soma,
- Jonathan J. Fortney,
- Raymond Pierrehumbert,
- David Lafrenière,
- Lorena Acuña,
- Thaddeus Komacek,
- Hamish Innes,
- Thomas G. Beatty,
- Ryan Cloutier,
- René Doyon,
- Anna Gagnebin,
- Cyril Gapp,
- Heather A. Knutson
Affiliations
- Caroline Piaulet-Ghorayeb
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Björn Benneke
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Michael Radica
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Eshan Raul
- ORCiD
- Department of Astronomy, University of Michigan , Ann Arbor, MI, USA
- Louis-Philippe Coulombe
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Eva-Maria Ahrer
- ORCiD
- Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
- Daria Kubyshkina
- ORCiD
- Space Research Institute , Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
- Ward S. Howard
- ORCiD
- Department of Astrophysical and Planetary Sciences, University of Colorado , 2000 Colorado Avenue, Boulder, CO 80309, USA
- Joshua Krissansen-Totton
- ORCiD
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington , Seattle, WA, USA
- Ryan J. MacDonald
- ORCiD
- Department of Astronomy, University of Michigan , Ann Arbor, MI, USA
- Pierre-Alexis Roy
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Amy Louca
- ORCiD
- Leiden Observatory, Leiden University , P.O. Box 9513, 2300 RA Leiden, The Netherlands; SRON Netherlands Institute for Space Research , Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
- Duncan Christie
- ORCiD
- Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
- Marylou Fournier-Tondreau
- ORCiD
- University of Oxford , Department of Physics Oxford, OX1 3PW, UK
- Romain Allart
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Yamila Miguel
- ORCiD
- Leiden Observatory, Leiden University , P.O. Box 9513, 2300 RA Leiden, The Netherlands; SRON Netherlands Institute for Space Research , Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
- Hilke E. Schlichting
- ORCiD
- Department of Earth, Planetary, and Space Sciences, University of California , Los Angeles, Los Angeles, CA 90095, USA
- Luis Welbanks
- ORCiD
- School of Earth & Space Exploration, Arizona State University , Tempe, AZ 85257, USA
- Charles Cadieux
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Caroline Dorn
- ORCiD
- Department of Physics and Institute for Particle Physics and Astrophysics , ETH Zurich, CH-8093 Zurich, Switzerland
- Thomas M. Evans-Soma
- ORCiD
- Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany; School of Information and Physical Sciences, University of Newcastle , Callaghan, NSW, Australia
- Jonathan J. Fortney
- ORCiD
- Department of Astronomy & Astrophysics, University of California , Santa Cruz, CA 95064, USA
- Raymond Pierrehumbert
- ORCiD
- University of Oxford , Department of Physics Oxford, OX1 3PW, UK
- David Lafrenière
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Lorena Acuña
- ORCiD
- Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
- Thaddeus Komacek
- ORCiD
- Department of Astronomy, University of Maryland , College Park, MD 20742, USA
- Hamish Innes
- ORCiD
- Department of Earth Sciences, Freie Universität Berlin , Malteserstr. 74-100, 12249 Berlin, Germany; Institute of Planetary Research , German Aerospace Center (DLR), Rutherfordstrae 2, 12489 Berlin, Germany
- Thomas G. Beatty
- ORCiD
- Department of Astronomy, University of Wisconsin–Madison , Madison, WI 53706, USA
- Ryan Cloutier
- ORCiD
- Department of Physics & Astronomy, McMaster University , 1280 Main Street W, Hamilton, ON L8S 4L8, Canada
- René Doyon
- ORCiD
- Department of Physics and Trottier Institute for Research on Exoplanets, Université de Montréal , Montreal, QC, Canada ; [email protected]
- Anna Gagnebin
- ORCiD
- Department of Astronomy & Astrophysics, University of California , Santa Cruz, CA 95064, USA
- Cyril Gapp
- ORCiD
- Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
- Heather A. Knutson
- ORCiD
- Division of Geological and Planetary Sciences, California Institute of Technology , Pasadena, CA 91125, USA
- DOI
- https://doi.org/10.3847/2041-8213/ad6f00
- Journal volume & issue
-
Vol. 974,
no. 1
p. L10
Abstract
With sizable volatile envelopes but smaller radii than the solar system ice giants, sub-Neptunes have been revealed as one of the most common types of planet in the galaxy. While the spectroscopic characterization of larger sub-Neptunes (2.5–4 R _⊕ ) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6–2.5 R _⊕ ) could either host thin, rapidly evaporating, hydrogen-rich atmospheres or be stable, metal-rich “water worlds” with high mean molecular weight atmospheres and a fundamentally different formation and evolutionary history. Here, we present the 0.6–2.8 μ m JWST/NIRISS/SOSS transmission spectrum of GJ 9827 d, the smallest (1.98 R _⊕ ) warm ( T _eq,A=0.3 ∼ 620 K) sub-Neptune where atmospheric absorbers have been detected to date. Our two transit observations with NIRISS/SOSS, combined with the existing HST/WFC3 spectrum, enable us to break the clouds–metallicity degeneracy. We detect water in a highly metal-enriched “steam world” atmosphere (O/H of ∼4 by mass and H _2 O found to be the background gas with a volume mixing ratio of >31%). We further show that these results are robust to stellar contamination through the transit light source effect. We do not detect escaping metastable He, which, combined with previous nondetections of escaping He and H, supports the steam atmosphere scenario. In water-rich atmospheres, hydrogen loss driven by water photolysis happens predominantly in the ionized form, which eludes observational constraints. We also detect several flares in the NIRISS/SOSS light curves with far-UV energies of the order of 10 ^30 erg, highlighting the active nature of the star. Further atmospheric characterization of GJ 9827 d probing carbon or sulfur species could reveal the origin of its high metal enrichment.
Keywords
- Exoplanet atmospheres
- Exoplanet atmospheric composition
- Exoplanet atmospheric evolution
- Exoplanet structure
- Planetary atmospheres
- Exoplanet astronomy
