Observability of hydrogen-rich exospheres in Earth-like exoplanets

Santos, Leonardo A. dos; Bourrier, V.; Ehrenreich, D.; Kameda, Shingo

doi:10.1051/0004-6361/201833392

Cited by 34 publications

(43 citation statements)

References 70 publications

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“…Furthermore, it is unclear in how far erosion processes have affected the atmospheric metallicity of extrasolar Neptune and Saturn-mass exoplanets (see, e.g., Owen & Lai 2018;dos Santos et al 2019;Armstrong et al 2020). The atmospheric properties of the eccentric WASP-117b could be illuminating here as well.…”

Section: Discussionmentioning

confidence: 99%

Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

Carone

Mollière

Zhou

et al. 2021

A&A

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Aims. We investigate the atmospheric composition of the long-period (Porb = 10 days) eccentric exo-Saturn WASP-117b. WASP-117b could be similar in atmospheric temperature and chemistry to WASP-107b. In mass and radius, WASP-117b is similar to WASP-39b, which allows a comparative study of these planets. Methods. We analyzed a near-infrared transmission spectrum of WASP-117b taken with the Hubble Space Telescope (HST) WFC3 G141, which was reduced with two independent pipelines. High-resolution measurements were taken with VLT/ESPRESSO in the optical. Results. We report the robust (3σ) detection of a water spectral feature. In a 1D atmosphere model with isothermal temperature, uniform cloud deck, and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity [Fe/H] = 2.58−0.37+0.26 and clear skies. The data are also consistent with a lower metallicity composition [Fe/H] < 1.75 and a cloud deck between 10−2.2 and 10−5.1 bar, but with weaker Bayesian preference. We retrieve a low CH4 abundance of <10−4 volume fraction within 1σ and <2 × 10−1 volume fraction within 3σ. We cannot constrain the equilibrium temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH4 with Kzz ≥ 108 cm2 s−1. We report indications of Na and K in the VLT/ESPRESSO high-resolution spectrum with substantial Bayesian evidence in combination with HST data.

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Section: Discussionmentioning

confidence: 99%

Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

Carone

Mollière

Zhou

et al. 2021

A&A

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“…TRAPPIST-1 would be right at the limit of capability of the instrument/telescope; and with LUVOIR/LUMOS to detect the presence of an hydrogen-rich exosphere in Lyman- (dos Santos et al. 2019 ). As a matter of fact, dos Santos et al.…”

Section: Future Prospectsmentioning

confidence: 99%

“…As a matter of fact, dos Santos et al. ( 2019 ) calculated that it would be possible to detect the exosphere of an Earth-like planet transiting TRAPPIST-1 at 5 within 10 transits using LUVOIR-A design with the LUMOS instrument concept.…”

Section: Future Prospectsmentioning

confidence: 99%

“…In an even more distant future, transit observations in UV could be attempted with UVSPEX, a conceptual design of Ultraviolet Spectrograph for Exoplanet (UVSPEX) for World Space Observatory Ultraviolet (WSO-UV), to detect the presence of an oxygen-rich exosphere . TRAPPIST-1 would be right at the limit of capability of the instrument/telescope; and with LUVOIR/LUMOS to detect the presence of an hydrogenrich exosphere in Lyman-α (dos Santos et al 2019). As a matter of fact, dos Santos et al (2019) calculated that it would be possible to detect the exosphere of an Earth-like planet transiting TRAPPIST-1 at 5σ within 10 transits using LUVOIR-A design with the LUMOS instrument concept.…”

Section: Future Prospectsmentioning

confidence: 99%

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A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

et al. 2020

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TRAPPIST-1 is a fantastic nearby (∼39.14 light years) planetary system made of at least seven transiting terrestrial-size, terrestrial-mass planets all receiving a moderate amount of irradiation. To date, this is the most observationally favourable system of potentially habitable planets known to exist. Since the announcement of the discovery of the TRAPPIST-1 planetary system in 2016, a growing number of techniques and approaches have been used and proposed to characterize its true nature. Here we have compiled a state-of-the-art overview of all the observational and theoretical constraints that have been obtained so far using these techniques and approaches. The goal is to get a better understanding of whether or not TRAPPIST-1 planets can have atmospheres, and if so, what they are made of. For this, we surveyed the literature on TRAPPIST-1 about topics as broad as irradiation environment, planet formation and migration, orbital stability, effects of tides and Transit Timing Variations, transit observations, stellar contamination, density measurements, and numerical climate and escape models. Each of these topics adds a brick to our understanding of the likely—or on the contrary unlikely—atmospheres of the seven known planets of the system. We show that (i) Hubble Space Telescope transit observations, (ii) bulk density measurements comparison with H 2 -rich planets mass-radius relationships, (iii) atmospheric escape modelling, and (iv) gas accretion modelling altogether offer solid evidence against the presence of hydrogen-dominated—cloud-free and cloudy—atmospheres around TRAPPIST-1 planets. This means that the planets are likely to have either (i) a high molecular weight atmosphere or (ii) no atmosphere at all. There are several key challenges ahead to characterize the bulk composition(s) of the atmospheres (if present) of TRAPPIST-1 planets. The main one so far is characterizing and correcting for the effects of stellar contamination. Fortunately, a new wave of observations with the James Webb Space Telescope and near-infrared high-resolution ground-based spectrographs on existing very large and forthcoming extremely large telescopes will bring significant advances in the coming decade.

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“…Furthermore, the hydrogen-rich atmosphere can appear in the early phase of Earth-like planets due to the process of outgassing or accretion (Elkins-Tanton & Seager 2008). The observational signals in Lyα for Earth-like planets have been discussed by dos Santos et al (2019) and Kislyakova et al (2019).…”

Section: Sample Selectedmentioning

confidence: 99%

The Escape of the Hydrogen-rich Atmosphere of Exoplanets: Mass-loss Rates and the Absorption of Stellar Lyα

Yan

Guo

2019

ApJ

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Since the mass loss rates are the function of the mean density of the planet and the stellar irradiation, we calculated about 450 models covering planets with different densities and stellar irradiation. Our results show that the mass loss rates are dependent on the stellar irradiation and the mean density. However, the mass loss rates predicted by the energy-limited equation are higher than that of hydrodynamic model when the XUV integrated flux is higher than ∼2×10 4 erg/cm 2 /s. The overestimation can be revised if the kinetic and thermal energy of the escaping atmosphere is included in the energy-limited equation. We found that the heating efficiencies are proportional to the product of the gravitational potential of the planet and the stellar irradiation. The mean absorption radii of stellar irradiation are 1.1-1.2 R p for the Jupiter-like planets while they vary in the range of 1.1-1.7 R p for the planets with smaller sizes. We evaluated the absorption of stellar Lyα by planetary atmosphere and found that the deeper Lyα absorptions tend to locate in the high stellar irradiation and low planetary mean density regions, and vice versa. Moreover, planets with mass loss rates higher than 10 11 g/s are likely to exhibit obvious absorptions. Finally, we suggested that the absorption levels are related to the inherent properties of the exoplanets. The planets with larger sizes (or lower mean density) show strong Lyα absorptions.Neptune-like and Earth-like planets tend to have weak Lyα absorptions because of their small sizes (or high densities).Subject headings: planets and satellites: atmosphere -planets and satellites: composition -planets and satellites: physical evolution R J are Neptune-like planets, 0.6-1.0 R J are Saturn-like planets. Finally, the planets with radius larger than 1.0 R J are Jupiter-like planets. Koskinen et al. (2007) suggests that the exoplanets with a separation smaller than 0.15AU will produce significant mass loss. Hence, we selected those planets that their separation are less than 0.1 AU. The separations are in the range of 0.01-0.09AU for Earth-like and Neptune-like planets, 0.04-0.07 AU for Saturn-like planets and 0.02-0.08AUfor Jupiter-like planets. The host stellar masses of each system are in the range of 0.08-1.105 M (M is the mass of the Sun) for Earth-like, 0.15-1.223 M for Neptune-like, 0.816-1.3

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Observability of hydrogen-rich exospheres in Earth-like exoplanets

Cited by 34 publications

References 70 publications

Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

The Escape of the Hydrogen-rich Atmosphere of Exoplanets: Mass-loss Rates and the Absorption of Stellar Lyα

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