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Detectable Molecular Features above Hydrocarbon Haze via Transmission Spectroscopy with JWST: Case Studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like Planets

Kawashima, Yui and Hu, Renyu and Ikoma, Masahiro (2019) Detectable Molecular Features above Hydrocarbon Haze via Transmission Spectroscopy with JWST: Case Studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like Planets. Astrophysical Journal Letters, 876 (1). Art. No. L5. ISSN 2041-8213. doi:10.3847/2041-8213/ab16f6.

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Some of the exoplanets observed thus far show featureless or flat transmission spectra, possibly indicating the existence of clouds and/or haze in their atmospheres. Thanks to its large aperture size and broad wavelength coverage, the James Webb Space Telescope (JWST) is expected to enable a detailed investigation of exoplanet atmospheres, which could provide important constraints on the atmospheric composition obscured by clouds/haze. Here, we use four warm (≾1000 K) planets suitable for atmospheric characterization via transmission spectroscopy, GJ 1214b, GJ 436b, HD 97658b, and Kepler-51b, as examples to explore molecular absorption features detectable by JWST even in the existence of hydrocarbon haze in the atmospheres. We simulate photochemistry, the growth of hydrocarbon haze particles, and transmission spectra for the atmospheres of these four planets. We find that among the planetary parameters considered, super-Earths with hazy, relatively hydrogen-rich atmospheres are mostly expected to produce detectable molecular absorption features such as a quite prominent CH_4 feature at 3.3 μm, even for the extreme case of the most efficient production of photochemical haze. For a planet that has extremely low gravity, such as Kepler-51b, haze particles grow significantly large in the upper atmosphere due to the small sedimentation velocity, resulting in the featureless or flat transmission spectrum in a wide wavelength range. This investigation shows that, in most cases, the transmission spectra with muted features measured by Hubble Space Telescope do not preclude strong features at the longer wavelengths accessible by JWST.

Item Type:Article
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URLURL TypeDescription Paper
Kawashima, Yui0000-0003-3800-7518
Hu, Renyu0000-0003-2215-8485
Ikoma, Masahiro0000-0002-5658-5971
Additional Information:© 2019 The American Astronomical Society. Received 2018 December 31; revised 2019 April 4; accepted 2019 April 8; published 2019 April 26. We thank the anonymous referee for a careful reading and constructive comments, which helped us improve this Letter greatly. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Y.K. thanks the travel support of JPL's Science Visitor and Colloquium Program. Y.K. is supported by the Grant-in-Aid for JSPS Fellow (JSPS KAKENHI No. 15J08463), Leading Graduate Course for Frontiers of Mathematical Sciences and Physics, Grant-in-Aid for Scientific Research (A) (JSPS KAKENHI No. 15H02065), and the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement 776403. R.H. is supported by NASA grant No. 80NM0018F0612. M.I. is supported by JSPS KAKENHI No. 18H05439 and Core-to-Core Program International Network of Planetary Sciences. This work has made use of the MUSCLES Treasury Survey High-Level Science Products (doi:10.17909/T9DG6F) and the SVO Filter Profile Service ( supported from the Spanish MINECO through grant AyA2014-55216.
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)15J08463
Japan Society for the Promotion of Science (JSPS)15H02065
European Research Council (ERC)776403
Japan Society for the Promotion of Science (JSPS)18H05439
Ministerio de Economía, Industria y Competitividad (MINECO)AyA2014-55216
Subject Keywords:planets and satellites: atmospheres – planets and satellites: composition – planets and satellites: individual (GJ 1214b, GJ 436b, HD 97658b, and Kepler-51b)
Issue or Number:1
Record Number:CaltechAUTHORS:20190426-104213316
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Official Citation:Yui Kawashima et al 2019 ApJL 876 L5
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95022
Deposited By: Tony Diaz
Deposited On:26 Apr 2019 18:05
Last Modified:16 Nov 2021 17:09

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