Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c

Gomes, Gabriel O.; Ferraz-Mello, S.

doi:10.1093/mnras/staa1110

Cited by 6 publications

(4 citation statements)

References 34 publications

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“…The K2-18 system is composed of at least another planet: K2-18 c (Cloutier et al 2019), orbiting closer to its star than K2-18b. Both planets may have a moderately high eccentricity that is rapidly evolving due to the secular interactions between the two objects (Gomes & Ferraz-Mello 2020). In that configuration, a lot of orbital energy can indeed be dissipated, but only in the innermost planet 8 , that is, K2-18 c. Thus, there should be no tidal heating on K2-18b.…”

Section: High Internal Temperaturementioning

confidence: 99%

1D atmospheric study of the temperate sub-Neptune K2-18b

Blain

Charnay

Bézard

2021

A&A

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Context. The atmospheric composition of exoplanets with masses between 2 and 10 M ⊕ is poorly understood. In that regard, the sub-Neptune K2-18b, which is subject to Earth-like stellar irradiation, offers a valuable opportunity for the characterisation of such atmospheres. Previous analyses of its transmission spectrum from the Kepler, Hubble (HST), and Spitzer space telescopes data using both retrieval algorithms and forward-modelling suggest the presence of H 2 O and an H 2-He atmosphere, but have not detected other gases, such as CH 4. Aims. We present simulations of the atmosphere of K2-18 b using Exo-REM, our self-consistent 1D radiative-equilibrium model, using a large grid of atmospheric parameters to infer constraints on its chemical composition. Methods. We compared the transmission spectra computed by our model with the above-mentioned data (0.4 to 5 µm), assuming an H 2-He dominated atmosphere. We investigated the effects of irradiation, eddy diffusion coefficient, internal temperature, clouds, C/O ratio, and metallicity on the atmospheric structure and transit spectrum. Results. We show that our simulations favour atmospheric metallicities between 40 and 500 times solar and indicate, in some cases, the formation of H 2 O-ice clouds, but not liquid H 2 O clouds. We also confirm the findings of our previous study, which showed that CH 4 absorption features nominally dominate the transmission spectrum in the HST spectral range. We compare our results with results from retrieval algorithms and find that the H 2 O-dominated spectrum interpretation is either due to the omission of CH 4 absorptions or a strong overfitting of the data. Finally, we investigated different scenarios that would allow for a CH 4-depleted atmosphere. We were able to fit the data to those scenarios, finding, however, that it is very unlikely for K2-18b to have a high internal temperature. A low C/O ratio (≈ 0.01-0.1) allows for H 2 O to dominate the transmission spectrum and can fit the data but so far, this setup lacks a physical explanation. Simulations with a C/O ratio < 0.01 are not able to fit the data satisfactorily.

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Section: High Internal Temperaturementioning

confidence: 99%

1D atmospheric study of the temperate sub-Neptune K2-18b

Blain

Charnay

Bézard

2021

A&A

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“…The transit component assumes circular orbits for both planets (Gomes & Ferraz-Mello 2020). The orbital parameters of planet k (k: "b", "c") are the period P k fixed to the value from Cadieux et al (2024), the time of inferior conjunction t 0,k , and the scaled semimajor axis a k /R å that we derive using a common stellar density ρ å .…”

Section: White Light-curve Analysismentioning

confidence: 99%

Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS

Cadieux,

Doyon,

MacDonald

et al. 2024

ApJL

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LHS 1140 b is the second-closest temperate transiting planet to Earth with an equilibrium temperature low enough to support surface liquid water. At 1.730 ± 0.025 R ⊕, LHS 1140 b falls within the radius valley separating H2-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 be either a mini-Neptune with a small envelope of hydrogen (∼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 (5.8σ), covering ∼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 a N2-dominated atmosphere (2.3σ), irrespective of the consideration of atmospheric hazes. We also show through Global Climate Models (GCMs) that H2-rich atmospheres of various compositions (100×, 300×, 1000× solar metallicity) are ruled out to >10σ. 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 a N2-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b.

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“…We may compare these values to the analogous values for Neptune: 3 − 19 s −1 . The large difference in the order of magnitude of the relaxation factors of gaseous and stiff planets may be used to decide, from the study of their putative tidal evolutions, if some potentially habitable small planet is a super-Earth or a mini-Neptune of the same size (Gomes and Ferraz-Mello, 2020).…”

Section: Small Planetsmentioning

confidence: 99%

On Tides and Exoplanets

Ferraz-Mello

2021

Preprint

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This paper reviews the basic equations used in the study of the tidal variations of the rotational and orbital elements of a system formed by one star and one close-in planet as given by the creep tide theory for homogeneous bodies and Darwin's constant time lag (CTL) theory. At the end, it reviews and discusses the determinations of the relaxation factors (and time lags) in the case of host stars and hot Jupiters based on actual observations of orbital decay, stellar rotation and age, etc. It also includes a recollection of the basic facts concerning the variations of the rotation of host stars due to the leakage of angular momentum associated with stellar winds.

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Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c

Cited by 6 publications

References 34 publications

1D atmospheric study of the temperate sub-Neptune K2-18b

1D atmospheric study of the temperate sub-Neptune K2-18b

Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS

On Tides and Exoplanets

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