Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

Vida, K.; Kővári, Zs.; Pál, András; Oláh, K.; Kriskovics, L.

doi:10.3847/1538-4357/aa6f05

Cited by 176 publications

(219 citation statements)

References 38 publications

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“…Stellar flares could occasionally increase the energy input into the atmospheres, enhancing the escape rate. However, no flaring activity was observed in TRAPPIST-1 X-ray and FUV observations, and the flares detected in optical (Luger et al 2017;Vida et al 2017) and infrared wavelengths point toward a low activity, with weak flares once every few days and stronger flares once every two to three months. The planetary atmospheres might also have been eroded by the stellar wind of TRAPPIST-1, especially when it was more active during the early phases of the system.…”

Section: Discussionmentioning

confidence: 99%

“…Figure 9 shows the present-day orbital distances of the seven planets and the evolution of the HZ inner limits for a TRAPPIST-1 analog. Using the mass of TRAPPIST-1 ( M 0.0802  ) yielded an HZ inner edge much closer to what is shown in Gillon et al (2017), because low-mass star evolution models tend to underestimate the luminosity for active stars (Chabrier et al 2007) such as TRAPPIST-1 (Luger et al 2017;Vida et al 2017). We therefore revised the stellar mass for TRAPPIST-1 following the prescription of Chabrier et al (2007), by greatly reducing convection efficiency in CLES (Code Liégeois d'Évolution Stellaire) stellar evolution models (Scuflaire et al 2008).…”

Section: Evolution Of the Planets Under High-energy Irradiationmentioning

confidence: 99%

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Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

et al. 2017

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The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Lyα line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST, they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.

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Section: Discussionmentioning

confidence: 99%

Section: Evolution Of the Planets Under High-energy Irradiationmentioning

confidence: 99%

Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

et al. 2017

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“…It should be noted that this description covers a situation during enhanced stellar activity, where M dwarfs can emit UV flux on the order of that emitted by the Sun (Segura et al 2005;Venot et al 2016). TRAPPIST-1, for example, shows indeed frequently increased activity (Vida et al 2017).…”

Section: Stratosphere Temperature Extension and Vertical Resolutionmentioning

confidence: 94%

Stratosphere circulation on tidally locked ExoEarths

Carone

Keppens

Decin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Stratosphere circulation is important to interpret abundances of photo-chemically produced compounds like ozone that we aim to observe to assess habitability of exoplanets. We thus investigate a tidally locked ExoEarth scenario for TRAPPIST-1b, TRAPPIST-1d, Proxima Centauri b and GJ 667 C f with a simplified 3D atmosphere model and for different stratospheric wind breaking assumptions.These planets are representatives for different circulation regimes for orbital periods: P or b = 1 − 100 days. The circulation of exoplanets with P or b 25 days can be dominated by the standing tropical Rossby wave in the troposphere and also in the stratosphere: It leads to a strong equatorial eastward wind jet and to 'Anti-Brewer-Dobson'-circulation that confines air masses to the stratospheric equatorial region. Thus, the distribution of photo-chemically produced species and aerosols may be limited to an 'equatorial transport belt'. In contrast, planets with P or b > 25 days, like GJ 667 C f, exhibit efficient thermally driven circulation in the stratosphere that allows for a day side-wide distribution of air masses.The influence of the standing tropical Rossby waves on tidally locked ExoEarths with P or b 25 days can, however, be circumvented with deep stratospheric wind breaking aloneallowing for equator-to-pole transport like on Earth. For planets with 3 P or b 6 days, the extratropical Rossby wave acts as an additional safe-guard against the tropical Rossby wave in case of shallow wind breaking. Therefore, TRAPPIST-1d is less prone to have an equatorial transport belt in the stratosphere than Proxima Centauri b. Even our Earth model shows an equatorial wind jet, if stratosphere wind breaking is inefficient.

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“…James Webb Space Telescope (JWST) transmission spectroscopy of a few dozen coadded transits of the TRAPPIST-1 planets b, c, and d, for instance, is expected to have sufficient sensitivity to detect O 3 in putative Earth-like atmospheres for these planets (Barstow & Irwin 2016). This makes these planets strong candidates for a biomarker detection within the next few years, but one should remember that the TRAPPIST-1 star emits intense extreme ultraviolet (XUV) radiation and frequently produces powerful stellar flares, which together might have sterilised, if not completely stripped out, the atmospheres of at least its closer-in planets (Bourrier et al 2017;Vida et al 2017). With stellar activity factored in, the quiet M dwarf LHS1140 and its temperate super-Earth become an appealing alternative.…”

Section: Introductionmentioning

confidence: 99%

A temperate exo-Earth around a quiet M dwarf at 3.4 parsec

Bonfils

Astudillo-Defru

Díaz

et al. 2018

A&A

122

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The combination of high-contrast imaging and high-dispersion spectroscopy, which has successfully been use to detect the atmosphere of a giant planet, is one of the most promising potential probes of the atmosphere of Earth-size worlds. The forthcoming generation of extremely large telescopes (ELTs) may obtain sufficient contrast with this technique to detect O2 in the atmosphere of those worlds that orbit low-mass M dwarfs. This is strong motivation to carry out a census of planets around cool stars for which habitable zones can be resolved by ELTs, i.e. for M dwarfs within ∼5 parsecs. Our HARPS survey has been a major contributor to that sample of nearby planets. Here we report on our radial velocity observations of Ross 128 (Proxima Virginis, GJ447, HIP 57548), an M4 dwarf just 3.4 parsec away from our Sun. This source hosts an exo-Earth with a projected mass m sin i = 1.35M⊕ and an orbital period of 9.9 days. Ross 128 b receives ∼1.38 times as much flux as Earth from the Sun and its equilibrium ranges in temperature between 269 K for an Earth-like albedo and 213 K for a Venus-like albedo. Recent studies place it close to the inner edge of the conventional habitable zone. An 80-day long light curve from K2 campaign C01 demonstrates that Ross 128 b does not transit. Together with the All Sky Automated Survey (ASAS) photometry and spectroscopic activity indices, the K2 photometry shows that Ross 128 rotates slowly and has weak magnetic activity. In a habitability context, this makes survival of its atmosphere against erosion more likely. Ross 128 b is the second closest known exo-Earth, after Proxima Centauri b (1.3 parsec), and the closest temperate planet known around a quiet star. The 15 mas planet-star angular separation at maximum elongation will be resolved by ELTs (> 3λ/D) in the optical bands of O2.

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Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life?

Cited by 176 publications

References 38 publications

Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

Stratosphere circulation on tidally locked ExoEarths

A temperate exo-Earth around a quiet M dwarf at 3.4 parsec

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