The Astronomical Journal (Jan 2024)
The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST
- Pa Chia Thao,
- Andrew W. Mann,
- Adina D. Feinstein,
- Peter Gao,
- Daniel Thorngren,
- Yoav Rotman,
- Luis Welbanks,
- Alexander Brown,
- Girish M. Duvvuri,
- Kevin France,
- Isabella Longo,
- Angeli Sandoval,
- P. Christian Schneider,
- David J. Wilson,
- Allison Youngblood,
- Andrew Vanderburg,
- Madyson G. Barber,
- Mackenna L. Wood,
- Natasha E. Batalha,
- Adam L. Kraus,
- Catriona Anne Murray,
- Elisabeth R. Newton,
- Aaron Rizzuto,
- Benjamin M. Tofflemire,
- Shang-Min Tsai,
- Jacob L. Bean,
- Zachory K. Berta-Thompson,
- Thomas M. Evans-Soma,
- Cynthia S. Froning,
- Eliza M.-R. Kempton,
- Yamila Miguel,
- J. Sebastian Pineda
Affiliations
- Pa Chia Thao
- ORCiD
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USA ; [email protected]
- Andrew W. Mann
- ORCiD
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USA ; [email protected]
- Adina D. Feinstein
- ORCiD
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , UCB 600, Boulder, CO 80309, USA; Department of Physics and Astronomy, Michigan State University , East Lansing, MI 48824, USA
- Peter Gao
- ORCiD
- Earth and Planets Laboratory, Carnegie Institution for Science , 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Daniel Thorngren
- ORCiD
- Department of Physics & Astronomy, Johns Hopkins University , Baltimore, MD, USA
- Yoav Rotman
- ORCiD
- School of Earth and Space Exploration, Arizona State University , Tempe, AZ 85281, USA
- Luis Welbanks
- ORCiD
- School of Earth and Space Exploration, Arizona State University , Tempe, AZ 85281, USA
- Alexander Brown
- ORCiD
- Center for Astrophysics and Space Astronomy, University of Colorado , 389 UCB, Boulder, CO 80309, USA
- Girish M. Duvvuri
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , Nashville, TN 37235, USA
- Kevin France
- ORCiD
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , UCB 600, Boulder, CO 80309, USA; Center for Astrophysics and Space Astronomy, University of Colorado , 389 UCB, Boulder, CO 80309, USA; Department of Astrophysical and Planetary Sciences, University of Colorado , UCB 389, Boulder, CO 80309, USA
- Isabella Longo
- ORCiD
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , UCB 600, Boulder, CO 80309, USA
- Angeli Sandoval
- ORCiD
- Astrophysics Program, The CUNY Graduate Center, City University of New York , New York, NY 10016, USA; Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- P. Christian Schneider
- ORCiD
- Hamburger Sternwarte, Gojenbergsweg 112, D-21029, Hamburg, Germany; Scientific Support Office, Directorate of Science, European Space Research and Technology Center (ESA/ESTEC) , Keplerlaan 1, 2201, AZNoordwijk, The Netherlands
- David J. Wilson
- ORCiD
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , UCB 600, Boulder, CO 80309, USA
- Allison Youngblood
- ORCiD
- Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- Andrew Vanderburg
- ORCiD
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139, USA
- Madyson G. Barber
- ORCiD
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USA ; [email protected]
- Mackenna L. Wood
- ORCiD
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USA ; [email protected]; MIT Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology , Cambridge, MA 02139, USA
- Natasha E. Batalha
- ORCiD
- NASA Ames Research Center , Moffett Field, CA 94035, USA
- Adam L. Kraus
- ORCiD
- Department of Astronomy, The University of Texas at Austin , Austin, TX 78712, USA
- Catriona Anne Murray
- ORCiD
- Department of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO, USA
- Elisabeth R. Newton
- ORCiD
- Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA
- Aaron Rizzuto
- ORCiD
- Mondo , Level 26/2 Southbank Blvd, Southbank VIC 3006, Australia
- Benjamin M. Tofflemire
- ORCiD
- Department of Astronomy, The University of Texas at Austin , Austin, TX 78712, USA
- Shang-Min Tsai
- ORCiD
- Department of Earth and Planetary Sciences, University of California , Riverside, CA, USA
- Jacob L. Bean
- ORCiD
- Department of Astronomy & Astrophysics, University of Chicago , Chicago, IL 60637, USA
- Zachory K. Berta-Thompson
- ORCiD
- Department of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO, USA
- Thomas M. Evans-Soma
- ORCiD
- School of Information and Physical Sciences, University of Newcastle , Callaghan, NSW, Australia; Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
- Cynthia S. Froning
- ORCiD
- Southwest Research Institute , Div. 05, 6220 Culebra Road, San Antonio, TX 78238, USA
- Eliza M.-R. Kempton
- ORCiD
- Department of Astronomy, University of Maryland , 4296 Stadium Drive, College Park, MD 20742, USA
- Yamila Miguel
- ORCiD
- Leiden Observatory, Leiden University , P.O. Box 9513, 2300 RA Leiden, NL, The Netherlands; SRON Netherlands Institute for Space Research , Niels Bohrweg 4, 2333 CA Leiden, NL, The Netherlands
- J. Sebastian Pineda
- ORCiD
- Laboratory for Atmospheric and Space Physics, University of Colorado Boulder , UCB 600, Boulder, CO 80309, USA
- DOI
- https://doi.org/10.3847/1538-3881/ad81d7
- Journal volume & issue
-
Vol. 168,
no. 6
p. 297
Abstract
The characterization of young planets (<300 Myr) is pivotal for understanding planet formation and evolution. We present the 3–5 μ m transmission spectrum of the 17 Myr, Jupiter-size ( R ∼10 R _⊕ ) planet, HIP 67522b, observed with JWST NIRSpec/G395H. To check for spot contamination, we obtain a simultaneous g -band transit with the Southern Astrophysical Research Telescope. The spectrum exhibits absorption features 30%–50% deeper than the overall depth, far larger than expected from an equivalent mature planet, and suggests that HIP 67522b’s mass is <20 M _⊕ irrespective of cloud cover and stellar contamination. A Bayesian retrieval analysis returns a mass constraint of 13.8 ± 1.0 M _⊕ . This challenges the previous classification of HIP 67522b as a hot Jupiter and instead, positions it as a precursor to the more common sub-Neptunes. With a density of <0.10 g cm ^−3 , HIP 67522 b is one of the lowest-density planets known. We find strong absorption from H _2 O and CO _2 (≥7 σ ), a modest detection of CO (3.5 σ ), and weak detections of H _2 S and SO _2 (≃2 σ ). Comparisons with radiative-convective equilibrium models suggest supersolar atmospheric metallicities and solar-to-subsolar C/O ratios, with photochemistry further constraining the inferred atmospheric metallicity to 3 × 10 solar due to the amplitude of the SO _2 feature. These results point to the formation of HIP 67522b beyond the water snowline, where its envelope was polluted by icy pebbles and planetesimals. The planet is likely experiencing substantial mass loss (0.01–0.03 M _⊕ Myr ^−1 ), sufficient for envelope destruction within a gigayear. This highlights the dramatic evolution occurring within the first 100 Myr of its existence.
Keywords
- Exoplanet atmospheric composition
- Exoplanet evolution
- James Webb Space Telescope
- Starspots
- Transmission spectroscopy
