Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS
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| Formato: | Preprint |
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2024
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| author | Cadieux, Charles Doyon, René MacDonald, Ryan J. Turbet, Martin Artigau, Étienne Lim, Olivia Radica, Michael Fauchez, Thomas J. Salhi, Salma Dang, Lisa Albert, Loïc Coulombe, Louis-Philippe Cowan, Nicolas B. Lafrenière, David L'Heureux, Alexandrine Piaulet, Caroline Benneke, Björn Cloutier, Ryan Charnay, Benjamin Cook, Neil J. Fournier-Tondreau, Marylou Plotnykov, Mykhaylo Valencia, Diana |
| author_facet | Cadieux, Charles Doyon, René MacDonald, Ryan J. Turbet, Martin Artigau, Étienne Lim, Olivia Radica, Michael Fauchez, Thomas J. Salhi, Salma Dang, Lisa Albert, Loïc Coulombe, Louis-Philippe Cowan, Nicolas B. Lafrenière, David L'Heureux, Alexandrine Piaulet, Caroline Benneke, Björn Cloutier, Ryan Charnay, Benjamin Cook, Neil J. Fournier-Tondreau, Marylou Plotnykov, Mykhaylo Valencia, Diana |
| contents | LHS 1140 b is the second-closest temperate transiting planet to the Earth with an equilibrium temperature low enough to support surface liquid water. At 1.730$\pm$0.025 R$_\oplus$, LHS 1140 b falls within the radius valley separating H$_2$-rich mini-Neptunes from rocky super-Earths. Recent mass and radius revisions indicate a bulk density significantly lower than expected for an Earth-like rocky interior, suggesting that LHS 1140 b could either be a mini-Neptune with a small envelope of hydrogen ($\sim$0.1% by mass) or a water world (9--19% water by mass). Atmospheric characterization through transmission spectroscopy can readily discern between these two scenarios. Here, we present two JWST/NIRISS transit observations of LHS 1140 b, one of which captures a serendipitous transit of LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows a telltale spectral signature of unocculted faculae (5.8 $σ$), covering $\sim$20% of the visible stellar surface. Besides faculae, our spectral retrieval analysis reveals tentative evidence of residual spectral features, best-fit by Rayleigh scattering from an N$_2$-dominated atmosphere (2.3 $σ$), irrespective of the consideration of atmospheric hazes. We also show through Global Climate Models (GCM) that H$_2$-rich atmospheres of various compositions (100$\times$, 300$\times$, 1000$\times$solar metallicity) are ruled out to $>$10 $σ$. The GCM calculations predict that water clouds form below the transit photosphere, limiting their impact on transmission data. Our observations suggest that LHS 1140 b is either airless or, more likely, surrounded by an atmosphere with a high mean molecular weight. Our tentative evidence of an N$_2$-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2406_15136 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS Cadieux, Charles Doyon, René MacDonald, Ryan J. Turbet, Martin Artigau, Étienne Lim, Olivia Radica, Michael Fauchez, Thomas J. Salhi, Salma Dang, Lisa Albert, Loïc Coulombe, Louis-Philippe Cowan, Nicolas B. Lafrenière, David L'Heureux, Alexandrine Piaulet, Caroline Benneke, Björn Cloutier, Ryan Charnay, Benjamin Cook, Neil J. Fournier-Tondreau, Marylou Plotnykov, Mykhaylo Valencia, Diana Earth and Planetary Astrophysics LHS 1140 b is the second-closest temperate transiting planet to the Earth with an equilibrium temperature low enough to support surface liquid water. At 1.730$\pm$0.025 R$_\oplus$, LHS 1140 b falls within the radius valley separating H$_2$-rich mini-Neptunes from rocky super-Earths. Recent mass and radius revisions indicate a bulk density significantly lower than expected for an Earth-like rocky interior, suggesting that LHS 1140 b could either be a mini-Neptune with a small envelope of hydrogen ($\sim$0.1% by mass) or a water world (9--19% water by mass). Atmospheric characterization through transmission spectroscopy can readily discern between these two scenarios. Here, we present two JWST/NIRISS transit observations of LHS 1140 b, one of which captures a serendipitous transit of LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows a telltale spectral signature of unocculted faculae (5.8 $σ$), covering $\sim$20% of the visible stellar surface. Besides faculae, our spectral retrieval analysis reveals tentative evidence of residual spectral features, best-fit by Rayleigh scattering from an N$_2$-dominated atmosphere (2.3 $σ$), irrespective of the consideration of atmospheric hazes. We also show through Global Climate Models (GCM) that H$_2$-rich atmospheres of various compositions (100$\times$, 300$\times$, 1000$\times$solar metallicity) are ruled out to $>$10 $σ$. The GCM calculations predict that water clouds form below the transit photosphere, limiting their impact on transmission data. Our observations suggest that LHS 1140 b is either airless or, more likely, surrounded by an atmosphere with a high mean molecular weight. Our tentative evidence of an N$_2$-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b. |
| title | Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2406.15136 |