The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST

The characterization of young planets (<300 Myr) is pivotal for understanding planet formation and evolution. We present the 3–5 μm transmission spectrum of the 17 Myr, Jupiter-size (R ∼10R ⊕) 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 H2O and CO2 (≥7σ), a modest detection of CO (3.5σ), and weak detections of H2S and SO2 (≃2σ). 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 SO2 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.

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Journal
UNC Libraries
Published
2024-12-17
DOI
https://doi.org/10.17615/1my1-4527
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
0.00

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article

The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST

Alexander Brown, Andrew W. Mann, Aaron C. Rizzuto, Benjamin M. Tofflemire et al.
UNC Libraries
Stellar, planetary, and galactic studies
article

The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST

Alexander Brown, Andrew W. Mann, Aaron C. Rizzuto, Benjamin M. Tofflemire, Zachory K. Berta-Thompson, Isabella Longo, Luis Welbanks, Elisabeth Newton, Madyson G. Barber, Kevin France, Adina D. Feinstein, Cynthia S. Froning, Eliza M.-R. Kempton, Girish M. Duvvuri, Peter Gao, T. M. Evans, Mackenna L. Wood, Jacob L. Bean, Yamila Miguel, Andrew Vanderburg, J. Sebastian Pineda, Daniel Thorngren, Angeli Sandoval, Shang‐Min Tsai, Pa Chia Thao, P. C. Schneider, Adam L. Kraus, Allison Youngblood, Yoav Rotman, David J. Wilson, Natasha Batalha, Catriona Anne Murray
article en

Abstract

The characterization of young planets (<300 Myr) is pivotal for understanding planet formation and evolution. We present the 3–5 μm transmission spectrum of the 17 Myr, Jupiter-size (R ∼10R ⊕) 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 H2O and CO2 (≥7σ), a modest detection of CO (3.5σ), and weak detections of H2S and SO2 (≃2σ). 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 SO2 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.

UNC Libraries
University of North Carolina at Chapel Hill (US)
National Science Foundation, National Aeronautics and Space Administration, North Carolina Space Grant, George Mason University, Michigan State University, Jack Kent Cooke Foundation, Space Telescope Science Institute, Ministério da Ciência, Tecnologia e Inovação, Nuclear Safety and Security Commission, Goddard Space Flight Center, College of Engineering, Michigan State University, University of North Carolina at Chapel Hill, Eurostars
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