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Published September 2019 | Accepted Version
Journal Article Open

Constraining Exoplanet Metallicities and Aerosols with ARIEL: An Independent Study by the Contribution to ARIEL Spectroscopy of Exoplanets (CASE) Team

Abstract

Launching in 2028, ESA's 0.64 m^2 Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL) survey of ~1000 transiting exoplanets will build on the legacies of NASA's Kepler and Transiting Exoplanet Survey Satellite (TESS), and complement the James Webb Space Telescope (JWST) by placing its high-precision exoplanet observations into a large, statistically significant planetary population context. With continuous 0.5–7.8 μm coverage from both FGS (0.5–0.6, 0.6–0.81, and 0.81–1.1 μm photometry; 1.1–1.95 μm spectroscopy) and AIRS (1.95–7.80 μm spectroscopy), ARIEL will determine atmospheric compositions and probe planetary formation histories during its 3.5 yr mission. NASA's proposed Contribution to ARIEL Spectroscopy of Exoplanets (CASE) would be a subsystem of ARIEL's Fine Guidance Sensor (FGS) instrument consisting of two visible-to-infrared detectors, associated readout electronics, and thermal control hardware. FGS, to be built by the Polish Academy of Sciences Space Research Centre, will provide both fine guiding and visible to near-infrared photometry and spectroscopy, providing powerful diagnostics of atmospheric aerosol contribution and planetary albedo, which play a crucial role in establishing planetary energy balance. The CASE team presents here an independent study of the capabilities of ARIEL to measure exoplanetary metallicities, which probe the conditions of planet formation, and FGS to measure scattering spectral slopes, which indicate if an exoplanet has atmospheric aerosols (clouds and hazes), and geometric albedos, which help establish planetary climate. Our simulations assume that ARIEL's performance will be 1.3× the photon-noise limit. This value is motivated by current transiting exoplanet observations: Spitzer/IRAC and Hubble/WFC3 have empirically achieved 1.15× the photon-noise limit. One could expect similar performance from ARIEL, JWST, and other proposed future missions such as HabEx, LUVOIR, and Origins. Our design reference mission simulations show that ARIEL could measure the mass–metallicity relationship of its 1000-planet single-visit sample to >7.5σ and that FGS could distinguish between clear, cloudy, and hazy skies and constrain an exoplanet's atmospheric aerosol composition to ≳5σ for hundreds of targets, providing statistically transformative science for exoplanet atmospheres.

Additional Information

© 2019 The Astronomical Society of the Pacific. Received 2019 January 25; accepted 2019 May 16; published 2019 August 20. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Copyright 2018. All rights reserved. We thank the JPL Exoplanet Science Initiative for partial support of this work. We thank the anonymous referee for their helpful comments. R.T.Z. would like to thank Giovanna Tinetti, Enzo Pascale, and Ingo Waldmann for their helpful discussions about the ARIEL mission and Taylor Bell for his input on current geometric albedo measurements. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

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August 19, 2023
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October 20, 2023