On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman-α monitoring

Castro, Ana Inés Gómez de; Beitia-Antero, Leire; Ustamujic, S.

doi:10.1007/s10686-018-9574-5

Cited by 8 publications

(9 citation statements)

References 42 publications

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“…Recently, Castro et al (2018) also studied if exospheres of Earth-like planets in the HZs of M dwarfs can be observable by World Space Observatory UV (WSO UV). They did not perform a modeling of the upper atmosphere and used a more simplified approach, however, still arriving at similar conclusions.…”

Section: Discussionmentioning

confidence: 99%

“…For higher XUV fluxes, they have adopted a hydrogen-dominated 1D atmosphere profile from Erkaev et al (2013), calculated using a similar version of the code we used to obtain atmospheric profiles for hydrogen-dominated atmospheres in the current article. For both cases, Castro et al (2018) did not take into account the interaction between the stellar wind and the neutral atmosphere. Even if a planet possesses a magnetic field, it may not protect the atmosphere from the dense and fast stellar wind of M dwarfs, which can sufficiently compress the atmosphere (e.g., Vidotto et al 2013) and lead to an interaction pattern similar to the one of a non-magnetized planet considered in this article.…”

Section: Discussionmentioning

confidence: 99%

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Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Kislyakova

Holmström

Odert

et al. 2019

A&A

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Aims. We modeled the transit signatures in the Lyman-alpha (Lyα) line of a putative Earth-sized planet orbiting in the habitable zone (HZ) of the M dwarf GJ 436. We estimated the transit depth in the Lyα line for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, a nitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with an amount of hydrogen equal to that of the Earth. For all types of atmospheres, we calculated the in-transit absorption they would produce in the stellar Lyα line. We applied it to the out-of-transit Lyα observations of GJ 436 obtained by the Hubble Space Telescope and compared the calculated in-transit absorption with observational uncertainties to determine if it would be detectable. To validate the model, we also used our method to simulate the deep absorption signature observed during the transit of GJ 436b and showed that our model is capable of reproducing the observations. Methods. We used a direct simulation Monte Carlo (DSMC) code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. It includes several ionization mechanisms, such as charge exchange with the stellar wind, photo-and electron impact ionization, and allows to trace particles collisions. At the lower boundary of the DSMC model we assumed an atmosphere density, temperature, and velocity obtained with a hydrodynamic model for the lower atmosphere. Results. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ 436 only the hydrogen-dominated atmosphere is marginally detectable with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). Neither a pure nitrogen atmosphere nor a nitrogen-dominated atmosphere with an Earth-like hydrogen concentration in the upper atmosphere are detectable. We also showed that the Lyα observations of GJ 436b can be reproduced reasonably well assuming a hydrogendominated atmosphere, both in the blue and red wings of the Lyα line, which indicates that warm Neptune-like planets are a suitable target for Lyα observations. Terrestrial planets, on the other hand, can be observed in the Lyα line if they orbit very nearby stars, or if several observational visits are available.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Kislyakova

Holmström

Odert

et al. 2019

A&A

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“…Taking the Earth as reference, it is well known from NASA's missions Magnetopause-to-Aurora Global Exploration (IMAGE) [32] and Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) [33] that Earth's exosphere extends much further than 30R ⊕ reaching a size comparable to the radius of a late M star (see Figure 11). As the exosphere's main component is atomic hydrogen, planetary exospheres efficiently block the Lyα (121.6 nm) radiation from the star [34]. In fact, in spite of the heavy interstellar absorption at Lyα, the transit of HD209458b, the first transiting planet was detected in Lyα with HST [31].…”

Section: Discussion: High Resolution Imaging Versus Transmission Specmentioning

confidence: 99%

“…Geosciences 2018, 8, 442 11 of 13 further than 30R reaching a size comparable to the radius of a late M star (see Figure 11). As the exosphere's main component is atomic hydrogen, planetary exospheres efficiently block the Lyα (121.6 nm) radiation from the star [34]. In fact, in spite of the heavy interstellar absorption at Lyα, the transit of HD209458b, the first transiting planet was detected in Lyα with HST [31].…”

Section: Discussion: High Resolution Imaging Versus Transmission Specmentioning

confidence: 99%

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Imaging and Characterization of Extrasolar Planets with the Next Generation of Space Telescopes

Castro¹

2018

Geosciences

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The study and characterization of the exoplanets’ atmospheres and composition is in its infancy. The large facilities that will make feasible to image an exo-Earth are currently under study. This contribution to the special issue on “detection and characterization of extrasolar planets” is a summary on the current status of the design studies to build large space-based facilities working in the 100–3000 nm range for this purpose. The three basic designs: Fresnel imagers, starshades, and coronagraphs on large space telescopes are described. An outline of the pros and cons for each design is provided. The relevance of transmission spectroscopy to characterize exoplanets atmospheres is pointed out.

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Observability of hydrogen-rich exospheres in Earth-like exoplanets

Santos

Bourrier

Ehrenreich

et al. 2019

A&A

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Context. The existence of an extended neutral hydrogen exosphere around small planets can be used as an evidence for the presence of water in their lower atmosphere but, to date, such feature has not been securely detected in rocky exoplanets. Planetary exospheres can be observed using transit spectroscopy of the Lyman-α line, which is limited mainly by interstellar medium absorption in the core of the line, and airglow contamination from the geocorona when using low-orbit space telescopes. Aims. Our objective is to assess the detectability of the neutral hydrogen exosphere of an Earth-like planet transiting a nearby M dwarf using Lyman-α spectroscopy and provide the necessary strategies to inform future observations. Methods. Our tests require spatial and velocity information of the neutral hydrogen particles in the upper atmosphere. The spatial distribution is provided by an empirical model of the geocorona, and we assume a velocity distribution based on radiative pressure as the main driver in shaping the exosphere. We compute the excess absorption in the stellar Lyman-α line while in transit, and use realistic estimates of the uncertainties involved in observations to determine the observability of the signal. Results. We found that the signal in Lyman-α of the exosphere of an Earth-like exoplanet transiting M dwarfs with radii between 0.1 and 0.6 R produces an excess absorption between 50 and 600 ppm. The Lyman-α flux of stars decays exponentially with distance because of interstellar medium absorption, which is the main observability limitation. Other limits are related to the stellar radial velocity and instrumental setup. Conclusions. The excess absorption in Lyman-α is observable using LUVOIR/LUMOS in M dwarfs up to a distance of ∼15 pc. The analysis of noise-injected data suggests that it would be possible to detect the exosphere of an Earth-like planet transiting TRAPPIST-1 within 20 transits.

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On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman-α monitoring

Cited by 8 publications

References 42 publications

Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Transit Lyman-α signatures of terrestrial planets in the habitable zones of M dwarfs

Imaging and Characterization of Extrasolar Planets with the Next Generation of Space Telescopes

Observability of hydrogen-rich exospheres in Earth-like exoplanets

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