Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

Wunderlich, Fabian; Godolt, M.; Grenfell, John Lee; Städt, Steffen; Smith, A. M. S.; Gebauer, S; Schreier, Franz; Hedelt, Pascal; Rauer, H.

doi:10.1051/0004-6361/201834504

Cited by 124 publications

(157 citation statements)

References 147 publications

(219 reference statements)

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“…In particular, the Prism mode of the NIRSPEC instrument shows a high potential to detect compact atmospheres around the planets (Batalha et al 2018;Lincowski et al 2018Lincowski et al , 2019Lustig-Yaeger et al 2019;Fauchez et al 2019b). Several independent simulations predict that it could take less than 10 transits for the seven planets to detect the dominant absorber (Morley et al 2017;Krissansen-Totton et al 2018;Lustig-Yaeger et al 2019;Wunderlich et al 2019;Batalha et al 2018). This number may increase if clouds and/or photochemical hazes are present (Fauchez et al 2019b).…”

Section: Model Fitted To the Datamentioning

confidence: 99%

“…The planets are good potential targets for atmospheric characterization with JWST (Lustig-Yaeger et al 2019;Lincowski et al 2018Lincowski et al , 2019Wunderlich et al 2019;Krissansen-Totton et al 2018; Barstow & Irwin 2016;Fauchez et al 2019b). Preliminary atmospheric prescreening was performed with HST/WFC3 and the resulting low-resolution transmission spectra acquired in the 1.1-1.7 µm spectral range made it possible to exclude clear hydrogen-dominated atmospheres for six of the seven planets (de Wit et al 2016(de Wit et al , 2018Wakeford et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

Ducrot

Gillon

Delrez

et al. 2020

A&A

113

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Context. With more than 1000 h of observation from Feb. 2016 to Oct. 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12 pc) ultracool dwarf star, finding that it is orbited by seven transiting Earth-sized planets. At least three of these planets orbit within the classical habitable zone of the star, and all of them are well-suited for a detailed atmospheric characterization with the upcoming JWST. Aims. The main goals of the Spitzer Red Worlds program were (1) to explore the system for new transiting planets, (2) to intensively monitor the planets’ transits to yield the strongest possible constraints on their masses, sizes, compositions, and dynamics, and (3) to assess the infrared variability of the host star. In this paper, we present the global results of the project. Methods. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 μm. For a comprehensive study, we analyzed all light curves both individually and globally. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 μm to constrain the brightness temperatures of their daysides. Results. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We do not detect any significant variation of the transit depths of the planets throughout the different campaigns. Comparing our individual and global analyses of the transits, we estimate for TRAPPIST-1 transit depth measurements mean noise floors of ~35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. We estimate that most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10 ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. Our analysis reveals a few outlier transits, but we cannot conclude whether or not they correspond to spot or faculae crossing events. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. Although we are limited by instrumental precision, the combined transmission spectrum of planet b to g tells us that their atmospheres seem unlikely to be CH4-dominated. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 μm, and can only set 3-σ upper limits on their dayside brightness temperatures (611 K for b 586 K for c).

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Section: Model Fitted To the Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

Ducrot

Gillon

Delrez

et al. 2020

A&A

113

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“…biosignatures would be difficult to detect on this planet. However, using simulations of Earth with M-dwarf host stars, Wunderlich et al (2019) find that the TRAPPIST-1 planets could have approximately an order of magnitude less O 3 and three orders of magnitude more CH 4 than Earth; this would make the CH 4 features much easier to detect, while slightly compromising the detectability of O 3 .…”

Section: Discussion: Habitability and Biosignaturesmentioning

confidence: 99%

“…Note that ∆t refers to the total in-transit integration time, which may exceed the duration of a single transit if several transits are combined (e.g., Kreidberg et al 2014). Lustig-Yaeger et al (2019); Wunderlich et al (2019) use more realistic noise models; however, eperience with the Hubble and Spitzer telescopes suggests that observers approach the photon limit shortward of 6 µm (Cowan et al 2015).…”

Section: Noisementioning

confidence: 99%

An empirical infrared transit spectrum of Earth: opacity windows and biosignatures

Macdonald

Cowan

2019

Monthly Notices of the Royal Astronomical Society

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The Atmospheric Chemistry Experiment's Fourier Transform Spectrometer on the SCISAT satellite has been measuring infrared transmission spectra of Earth during Solar occultations since 2004. We use these data to build an infrared transit spectrum of Earth. Regions of low atmospheric opacity, known as windows, are of particular interest, as they permit observations of the planet's lower atmosphere. Even in the absence of clouds or refraction, imperfect transmittance leads to a minimum effective thickness of h min ≈ 4 km in the 10-12 µm opacity window at a spectral resolution of R = 10 3 . Nonetheless, at R = 10 5 , the maximum transmittance at the surface is around 70 %. In principle, one can probe the troposphere of an Earth-like planet via high-dispersion transit spectroscopy in the mid-infrared; in practice aerosols and/or refraction likely make this impossible. We simulate the transit spectrum of an Earth-like planet in the TRAPPIST-1 system. We find that a long-term near-infrared campaign with JWST could readily detect CO 2 and H 2 O, establishing the presence of an atmosphere. A mid-IR campaign or longer NIR campaign would be more challenging, but in principle could detect the biosignatures O 3 and CH 4 .

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“…For the M-dwarf Earth-like planets (henceforth called "M-Earths") we use data from Wunderlich et al (2019); also see (in contrast to Earth where the VMR decreases by about a factor 10 from BoA to ToA). As discussed by Wunderlich et al (2019), CH 4 is strongly enhanced, with vertical column densities ranging from 6 · 10 21 cm −2 for "Earth" placed around GJ644 to 7 · 10 22 cm −2 for Earth around Trappist 1 -compared to 3.5·10 19 cm −2 or 1.6 ppm for the mean Garand atmosphere (modern Earth). Nitrous oxide (N 2 O) concentrations are also larger compared to Earth, especially in the upper atmosphere.…”

Section: Input Datamentioning

confidence: 99%

SVEEEETIES: singular vector expansion to estimate Earth-like exoplanet temperatures from infrared emission spectra

Schreier

Städt

Wunderlich

et al. 2020

A&A

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Context. Detailed characterizations of exoplanets are clearly moving to the forefront of planetary science. Temperature is a key marker for understanding atmospheric physics and chemistry. Aims. We aim to retrieve temperatures of N 2 -O 2 dominated atmospheres from secondary eclipse spectroscopic observations of the thermal emission of Earth-like exoplanets orbiting G-, K-, and M-stars, using large-aperture future space telescopes. Methods. A line-by-line radiative transfer code was used to generate synthetic thermal infrared (TIR) observations. The atmospheric temperature is approximated by an expansion with the base vectors defined by a singular value decomposition of a matrix comprising representative profiles. A nonlinear least squares fitting was used to estimate the unknown expansion coefficients. Results. Analysis of the 4.3 µm and 15 µm CO 2 bands in the TIR spectra permits the inference of temperatures even for low signalto-noise ratios (S/N) of 5 at medium resolution. Deviations from the true temperature in the upper troposphere and lower-to-mid stratosphere are usually in the range of a few Kelvin, with larger deviations in the upper atmosphere and, less often, in the lower troposphere. Although the performance of the two bands is equivalent in most cases, the longwave TIR is more favorable than the shortwave due to increased star-planet contrast. A high spectral resolution, as provided by the James Webb Space Telescope (JWST) instruments, is important for retaining sensitivity to the upper atmosphere. Furthermore, the selection of an appropriate set of base functions is also key. Conclusions. Temperature in the mid-atmosphere, relevant for understanding habitability, can be suitably characterized by infrared emission spectroscopy with a resolution of at least 1000 (ideally ≈2500). Obtaining the necessary S/N will be challenging even for JWST, however, it could be feasible with future space missions, such as the Origins Space Telescope or the Large Interferometer for Exoplanets. In the meantime, a least squares fitting with an appropriate set of base functions is also applicable for other classes of planets.

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Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

Cited by 124 publications

References 147 publications

TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

An empirical infrared transit spectrum of Earth: opacity windows and biosignatures

SVEEEETIES: singular vector expansion to estimate Earth-like exoplanet temperatures from infrared emission spectra

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