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      Detecting the proposed CH4–CO2 biosignature pair with the James Webb Space Telescope: TRAPPIST-1e and the effect of cloud/haze

      1 , 2
      Monthly Notices of the Royal Astronomical Society
      Oxford University Press (OUP)

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          ABSTRACT

          It is widely anticipated that the James Webb Space Telescope (JWST) will be transformative for exoplanet studies. It has even been suggested that JWST could provide the first opportunity to search for biosignatures in an alien atmosphere using transmission spectroscopy. This claim is investigated, specifically for the proposed anoxic biosignature pair CH4–CO2. The most favourable known target is adopted (TRAPPIST-1e), with an assumed atmospheric composition similar to the Archean Earth. Compared to previous studies, a more systematic investigation of the effect that cloud/haze layers have on the detectability of CH4 and CO2 is performed. In addition to a clear atmosphere scenario, cloud/haze layers are considered at eight pressure levels between 600 and 1 mbar. These pressures cover a plausible range for H2O cloud and photochemical haze, based on observations of solar system atmospheres and physical models of tidally locked planets such as TRAPPIST-1e, although no assumptions regarding the cloud/haze-layer composition are made in this study. For the clear atmosphere and cloud/haze-layer pressures of 600–100 mbar, strong (5σ) detections of both CH4 and CO2 are found to be possible with approximately 5–10 co-added transits measured using the Near Infrared Spectrograph (NIRSpec) prism, assuming a dry stratosphere. However, approximately 30 co-added transits would be required to achieve the same result if a cloud/haze layer is present at 10 mbar. A cloud/haze layer at 1 mbar would prevent the detection of either molecule with the NIRSpec prism for observing programmes up to 50 transits (>200 h of JWST time), the maximum considered.

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          X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue

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            A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion

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              Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b.

              Recent surveys have revealed that planets intermediate in size between Earth and Neptune ('super-Earths') are among the most common planets in the Galaxy. Atmospheric studies are the next step towards developing a comprehensive understanding of this new class of object. Much effort has been focused on using transmission spectroscopy to characterize the atmosphere of the super-Earth archetype GJ 1214b (refs 7 - 17), but previous observations did not have sufficient precision to distinguish between two interpretations for the atmosphere. The planet's atmosphere could be dominated by relatively heavy molecules, such as water (for example, a 100 per cent water vapour composition), or it could contain high-altitude clouds that obscure its lower layers. Here we report a measurement of the transmission spectrum of GJ 1214b at near-infrared wavelengths that definitively resolves this ambiguity. The data, obtained with the Hubble Space Telescope, are sufficiently precise to detect absorption features from a high mean-molecular-mass atmosphere. The observed spectrum, however, is featureless. We rule out cloud-free atmospheric models with compositions dominated by water, methane, carbon monoxide, nitrogen or carbon dioxide at greater than 5σ confidence. The planet's atmosphere must contain clouds to be consistent with the data.
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                Author and article information

                Contributors
                (View ORCID Profile)
                Journal
                Monthly Notices of the Royal Astronomical Society
                Oxford University Press (OUP)
                0035-8711
                1365-2966
                February 2022
                December 23 2021
                February 2022
                December 23 2021
                November 24 2021
                : 510
                : 1
                : 980-991
                Affiliations
                [1 ]Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
                [2 ]Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
                Article
                10.1093/mnras/stab3383
                92cc630f-f380-47ba-80d9-ffde1001be6d
                © 2021

                https://creativecommons.org/licenses/by/4.0/

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