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Detecting Biosignatures in the Atmospheres of Gas Dwarf Planets with the James Webb Space Telescope

Phillips, Caprice L. and Wang, Ji and Kendrew, Sarah and Greene, Thomas P. and Hu, Renyu and Valenti, Jeff and Panero, Wendy R. and Schulze, Joseph (2021) Detecting Biosignatures in the Atmospheres of Gas Dwarf Planets with the James Webb Space Telescope. Astrophysical Journal, 923 (2). Art. No. 144. ISSN 0004-637X. doi:10.3847/1538-4357/ac29be.

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Exoplanets with radii between those of Earth and Neptune have stronger surface gravity than Earth, and can retain a sizable hydrogen-dominated atmosphere. In contrast to gas giant planets, we call these planets gas dwarf planets. The James Webb Space Telescope (JWST) will offer unprecedented insight into these planets. Here, we investigate the detectability of ammonia (NH₃, a potential biosignature) in the atmospheres of seven temperate gas dwarf planets using various JWST instruments. We use petitRadTRANS and PandExo to model planet atmospheres and simulate JWST observations under different scenarios by varying cloud conditions, mean molecular weights (MMWs), and NH₃ mixing ratios. A metric is defined to quantify detection significance and provide a ranked list for JWST observations in search of biosignatures in gas dwarf planets. It is very challenging to search for the 10.3–10.8 μm NH₃ feature using eclipse spectroscopy with the Mid-Infrared Instrument (MIRI) in the presence of photon and a systemic noise floor of 12.6 ppm for 10 eclipses. NIRISS, NIRSpec, and MIRI are feasible for transmission spectroscopy to detect NH3 features from 1.5–6.1 μm under optimal conditions such as a clear atmosphere and low MMWs for a number of gas dwarf planets. We provide examples of retrieval analyses to further support the detection metric that we use. Our study shows that searching for potential biosignatures such as NH₃ is feasible with a reasonable investment of JWST time for gas dwarf planets given optimal atmospheric conditions.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Phillips, Caprice L.0000-0001-5610-5328
Wang, Ji0000-0002-4361-8885
Kendrew, Sarah0000-0002-7612-0469
Greene, Thomas P.0000-0002-8963-8056
Hu, Renyu0000-0003-2215-8485
Valenti, Jeff0000-0003-3305-6281
Panero, Wendy R.0000-0001-5753-2532
Schulze, Joseph0000-0003-3570-422X
Additional Information:© 2021. The American Astronomical Society. Received 2021 May 27; revised 2021 September 18; accepted 2021 September 22; published 2021 December 16. This work benefited from involvement in ExoExplorers, which is sponsored by the Exoplanets Program Analysis Group (ExoPAG) and NASAs Exoplanet Exploration Program Office (ExEP). The authors also wish to thank Victoria Meadows and Natasha Batalha for their helpful advice and suggestions for this manuscript. C. P. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; her participation in the program has benefited this work. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement We thank the anonymous referee for their time providing helpful comments that improved the quality of this paper. 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. This project is supported, in part, by funding from Two Sigma Investments, LP. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of Two Sigma Investments, LP. NASA's Astrophysics Data System Bibliographic Services together with the VizieR catalog access tool and SIMBAD database operated at CDS, Strasbourg, France, were invaluable resources for this work. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Facility: Exoplanet Archive - . Software: Pandexo (Batalha et al. 2017), petitRADTRANS (Mollière et al. 2019).
Funding AgencyGrant Number
Large Synoptic Survey Telescope CorporationUNSPECIFIED
Brinson FoundationUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Two Sigma Investments, LPUNSPECIFIED
Subject Keywords:Biosignatures; Astrobiology; Exoplanet atmospheres; Exoplanet atmospheric composition; Planetary atmospheres; Chemical abundances; Abundance ratios
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Biosignatures (2018); Astrobiology (74); Exoplanet atmospheres (487); Exoplanet atmospheric composition (2021); Planetary atmospheres (1244); Chemical abundances (224); Abundance ratios (11)
Record Number:CaltechAUTHORS:20211220-495675000
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Official Citation:Caprice L. Phillips et al 2021 ApJ 923 144
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112562
Deposited By: George Porter
Deposited On:20 Dec 2021 23:42
Last Modified:20 Dec 2021 23:42

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