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Observing Oceans in Tightly Packed Planetary Systems: Perspectives from Polarization Modeling of the TRAPPIST-1 System

Kopparla, Pushkar and Natraj, Vijay and Crisp, David and Bott, Kimberly and Swain, Mark R. and Yung, Yuk L. (2018) Observing Oceans in Tightly Packed Planetary Systems: Perspectives from Polarization Modeling of the TRAPPIST-1 System. Astronomical Journal, 156 (4). Art. No. 143. ISSN 1538-3881. doi:10.3847/1538-3881/aad9a1.

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The recently discovered TRAPPIST-1 system is exciting due to the possibility of several rocky, Earth-sized planets harboring liquid water on their surface. To assess the detectability of oceans on these planets, we model the disk-integrated phase curves and polarization signals for planets in this system for reflected starlight. We examine four cases: (1) dry planet, (2) cloud-covered planet, (3) planet with regional-scale oceans, and (4) planet with global oceans. Polarization signals are strongest for optically thin (≾ 0.1) atmospheres over widespread oceans, with the degree of polarization being up to 90% for a single planet or on the order of 100 parts per billion for the star–planet system. In cases where reflected light from different planets in a tightly packed system cannot be separated, observing in polarized light allows for up to a tenfold increase in star–planet contrast compared to photometric observations alone. However, polarization from other sources, such as atmospheric scattering and cloud variability, will pose major challenges to the detection of glint (specularly reflected starlight) polarization signals. Planned telescopes like LUVOIR may be capable of observing glint from Earth-like planets around Sun-like stars, and if equipped with a polarimeter can significantly improve our ability to detect and study oceans on rocky exoplanets.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kopparla, Pushkar0000-0002-8951-3907
Natraj, Vijay0000-0003-3154-9429
Crisp, David0000-0002-4573-9998
Swain, Mark R.0000-0002-0919-4468
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2018. The American Astronomical Society. Received 2018 February 21; revised 2018 August 8; accepted 2018 August 8; published 2018 September 10. We thank Peter Gao for insightful comments and Sloane Wiktorowicz for giving us an observer's perspective on the model results. We also want to thank the anonymous reviewer for their extraordinary commitment to helping us improve this paper. This research was supported in part by an NAI Virtual Planetary Laboratory grant from the University of Washington to the Jet Propulsion Laboratory (JPL) and California Institute of Technology (CIT), and in part by JPL. P.K., M.R.S., and Y.L.Y. acknowledge support from the President's and Director's Fund of CIT and JPL. We acknowledge use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at We thank Jeremy Bailey, Lucyna Chudczer, and Kim Bott for helping discover a bug in our model code.
Group:Astronomy Department
Funding AgencyGrant Number
University of WashingtonUNSPECIFIED
JPL President and Director's FundUNSPECIFIED
Subject Keywords:planetary systems; planets and satellites: oceans; polarization
Issue or Number:4
Record Number:CaltechAUTHORS:20190102-155140312
Persistent URL:
Official Citation:Pushkar Kopparla et al 2018 AJ 156 143
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92022
Deposited By: George Porter
Deposited On:03 Jan 2019 16:24
Last Modified:16 Nov 2021 03:46

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