JWST Reveals CH$_4$, CO$_2$, and H$_2$O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet
Fuente:
arXiv
Enregistré dans:
| Auteurs principaux: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Preprint |
| Publié: |
2024
|
| Sujets: | |
| Accès en ligne: | |
| Tags: |
Ajouter un tag
Pas de tags, Soyez le premier à ajouter un tag!
|
| _version_ | 1866914704747659264 |
|---|---|
| author | Benneke, Björn Roy, Pierre-Alexis Coulombe, Louis-Philippe Radica, Michael Piaulet, Caroline Ahrer, Eva-Maria Pierrehumbert, Raymond Krissansen-Totton, Joshua Schlichting, Hilke E. Hu, Renyu Yang, Jeehyun Christie, Duncan Thorngren, Daniel Young, Edward D. Pelletier, Stefan Knutson, Heather A. Miguel, Yamila Evans-Soma, Thomas M. Dorn, Caroline Gagnebin, Anna Fortney, Jonathan J. Komacek, Thaddeus MacDonald, Ryan Raul, Eshan Cloutier, Ryan Acuna, Lorena Lafrenière, David Cadieux, Charles Doyon, René Welbanks, Luis Allart, Romain |
| author_facet | Benneke, Björn Roy, Pierre-Alexis Coulombe, Louis-Philippe Radica, Michael Piaulet, Caroline Ahrer, Eva-Maria Pierrehumbert, Raymond Krissansen-Totton, Joshua Schlichting, Hilke E. Hu, Renyu Yang, Jeehyun Christie, Duncan Thorngren, Daniel Young, Edward D. Pelletier, Stefan Knutson, Heather A. Miguel, Yamila Evans-Soma, Thomas M. Dorn, Caroline Gagnebin, Anna Fortney, Jonathan J. Komacek, Thaddeus MacDonald, Ryan Raul, Eshan Cloutier, Ryan Acuna, Lorena Lafrenière, David Cadieux, Charles Doyon, René Welbanks, Luis Allart, Romain |
| contents | Even though sub-Neptunes likely represent the most common outcome of planet formation, their natures remain poorly understood. In particular, planets near 1.5-2.5$\,R_\oplus$ often have bulk densities that can be explained equally well with widely different compositions and interior structures, resulting in grossly divergent implications for their formation. Here, we present the full 0.6-5.2$\,μ\mathrm{m}$ JWST NIRISS/SOSS+NIRSpec/G395H transmission spectrum of the 2.2$\,R_\oplus$ TOI-270d ($4.78\,M_\oplus$, $T_\mathrm{eq}$=350-380 K), delivering unprecedented sensitivity for atmospheric characterization in the sub-Neptune regime. We detect five vibrational bands of CH$_4$ at 1.15, 1.4, 1.7, 2.3, and 3.3$\,μ$m (9.4$σ$), the signature of CO$_2$ at 4.3$\,μ$m (4.8$σ$), water vapor (2.5$σ$), and potential signatures of SO$_2$ at 4.0$\,μ\mathrm{m}$ and CS$_2$ at 4.6$\,μ\mathrm{m}$. Intriguingly, we find an overall highly metal-rich atmosphere, with a mean molecular weight of $5.47_{-1.14}^{+1.25}$. We infer an atmospheric metal mass fraction of $58_{-12}^{+8}\%$ and a C/O of $0.47_{-0.19}^{+0.16}$, indicating that approximately half the mass of the outer envelope is in high-molecular-weight volatiles (H$_2$O, CH$_4$, CO, CO$_2$) rather than H$_2$/He. We introduce a sub-Neptune classification scheme and identify TOI-270d as a "miscible-envelope sub-Neptune" in which H$_2$/He is well-mixed with the high-molecular-weight volatiles in a miscible supercritical metal-rich envelope. For a fully miscible envelope, we conclude that TOI-270d's interior is $90_{-4}^{+3}\,$wt$\,\%$ rock/iron, indicating that it formed as a rocky planet that accreted a few wt % of H$_2$/He, with the overall envelope metal content explained by magma-ocean/envelope reactions without the need for significant ice accretion. TOI-270d may well be an archetype of the overall population of sub-Neptunes. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2403_03325 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | JWST Reveals CH$_4$, CO$_2$, and H$_2$O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet Benneke, Björn Roy, Pierre-Alexis Coulombe, Louis-Philippe Radica, Michael Piaulet, Caroline Ahrer, Eva-Maria Pierrehumbert, Raymond Krissansen-Totton, Joshua Schlichting, Hilke E. Hu, Renyu Yang, Jeehyun Christie, Duncan Thorngren, Daniel Young, Edward D. Pelletier, Stefan Knutson, Heather A. Miguel, Yamila Evans-Soma, Thomas M. Dorn, Caroline Gagnebin, Anna Fortney, Jonathan J. Komacek, Thaddeus MacDonald, Ryan Raul, Eshan Cloutier, Ryan Acuna, Lorena Lafrenière, David Cadieux, Charles Doyon, René Welbanks, Luis Allart, Romain Earth and Planetary Astrophysics Even though sub-Neptunes likely represent the most common outcome of planet formation, their natures remain poorly understood. In particular, planets near 1.5-2.5$\,R_\oplus$ often have bulk densities that can be explained equally well with widely different compositions and interior structures, resulting in grossly divergent implications for their formation. Here, we present the full 0.6-5.2$\,μ\mathrm{m}$ JWST NIRISS/SOSS+NIRSpec/G395H transmission spectrum of the 2.2$\,R_\oplus$ TOI-270d ($4.78\,M_\oplus$, $T_\mathrm{eq}$=350-380 K), delivering unprecedented sensitivity for atmospheric characterization in the sub-Neptune regime. We detect five vibrational bands of CH$_4$ at 1.15, 1.4, 1.7, 2.3, and 3.3$\,μ$m (9.4$σ$), the signature of CO$_2$ at 4.3$\,μ$m (4.8$σ$), water vapor (2.5$σ$), and potential signatures of SO$_2$ at 4.0$\,μ\mathrm{m}$ and CS$_2$ at 4.6$\,μ\mathrm{m}$. Intriguingly, we find an overall highly metal-rich atmosphere, with a mean molecular weight of $5.47_{-1.14}^{+1.25}$. We infer an atmospheric metal mass fraction of $58_{-12}^{+8}\%$ and a C/O of $0.47_{-0.19}^{+0.16}$, indicating that approximately half the mass of the outer envelope is in high-molecular-weight volatiles (H$_2$O, CH$_4$, CO, CO$_2$) rather than H$_2$/He. We introduce a sub-Neptune classification scheme and identify TOI-270d as a "miscible-envelope sub-Neptune" in which H$_2$/He is well-mixed with the high-molecular-weight volatiles in a miscible supercritical metal-rich envelope. For a fully miscible envelope, we conclude that TOI-270d's interior is $90_{-4}^{+3}\,$wt$\,\%$ rock/iron, indicating that it formed as a rocky planet that accreted a few wt % of H$_2$/He, with the overall envelope metal content explained by magma-ocean/envelope reactions without the need for significant ice accretion. TOI-270d may well be an archetype of the overall population of sub-Neptunes. |
| title | JWST Reveals CH$_4$, CO$_2$, and H$_2$O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2403.03325 |