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| Format: | Preprint |
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2024
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| Online Access: | https://arxiv.org/abs/2410.03527 |
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| _version_ | 1866914964734738432 |
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| author | Piaulet-Ghorayeb, Caroline Benneke, Bjorn Radica, Michael Raul, Eshan Coulombe, Louis-Philippe Ahrer, Eva-Maria Kubyshkina, Daria Howard, Ward S. Krissansen-Totton, Joshua MacDonald, Ryan Roy, Pierre-Alexis Louca, Amy Christie, Duncan Fournier-Tondreau, Marylou Allart, Romain Miguel, Yamila Schlichting, Hilke E. Welbanks, Luis Cadieux, Charles Dorn, Caroline Evans-Soma, Thomas M. Fortney, Jonathan J. Pierrehumbert, Raymond Lafreniere, David Acuna, Lorena Komacek, Thaddeus Innes, Hamish Beatty, Thomas G. Cloutier, Ryan Doyon, Rene Gagnebin, Anna Gapp, Cyril Knutson, Heather A. |
| author_facet | Piaulet-Ghorayeb, Caroline Benneke, Bjorn Radica, Michael Raul, Eshan Coulombe, Louis-Philippe Ahrer, Eva-Maria Kubyshkina, Daria Howard, Ward S. Krissansen-Totton, Joshua MacDonald, Ryan Roy, Pierre-Alexis Louca, Amy Christie, Duncan Fournier-Tondreau, Marylou Allart, Romain Miguel, Yamila Schlichting, Hilke E. Welbanks, Luis Cadieux, Charles Dorn, Caroline Evans-Soma, Thomas M. Fortney, Jonathan J. Pierrehumbert, Raymond Lafreniere, David Acuna, Lorena Komacek, Thaddeus Innes, Hamish Beatty, Thomas G. Cloutier, Ryan Doyon, Rene Gagnebin, Anna Gapp, Cyril Knutson, Heather A. |
| contents | 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 (2.5-4R$_\oplus$) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6--2.5R$_\oplus$) 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$_\oplus$) warm (T$_\mathrm{eq, A_B=0.3} \sim 620$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 $\sim 4$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_03527 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d Piaulet-Ghorayeb, Caroline Benneke, Bjorn Radica, Michael Raul, Eshan Coulombe, Louis-Philippe Ahrer, Eva-Maria Kubyshkina, Daria Howard, Ward S. Krissansen-Totton, Joshua MacDonald, Ryan Roy, Pierre-Alexis Louca, Amy Christie, Duncan Fournier-Tondreau, Marylou Allart, Romain Miguel, Yamila Schlichting, Hilke E. Welbanks, Luis Cadieux, Charles Dorn, Caroline Evans-Soma, Thomas M. Fortney, Jonathan J. Pierrehumbert, Raymond Lafreniere, David Acuna, Lorena Komacek, Thaddeus Innes, Hamish Beatty, Thomas G. Cloutier, Ryan Doyon, Rene Gagnebin, Anna Gapp, Cyril Knutson, Heather A. Earth and Planetary Astrophysics Solar and Stellar Astrophysics 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 (2.5-4R$_\oplus$) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6--2.5R$_\oplus$) 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$_\oplus$) warm (T$_\mathrm{eq, A_B=0.3} \sim 620$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 $\sim 4$ 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. |
| title | JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2410.03527 |