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Earth as a Proxy Exoplanet: Deconstructing and Reconstructing Spectrophotometric Light Curves

Gu, Lixiang and Fan, Siteng and Li, Jiazheng and Bartlett, Stuart J. and Natraj, Vijay and Jiang, Jonathan H. and Crisp, David and Hu, Yongyun and Tinetti, Giovanna and Yung, Yuk L. (2021) Earth as a Proxy Exoplanet: Deconstructing and Reconstructing Spectrophotometric Light Curves. Astronomical Journal, 161 (3). Art. No. 122. ISSN 0004-6256. https://resolver.caltech.edu/CaltechAUTHORS:20210223-090759375

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Abstract

Point-source spectrophotometric (single-point) light curves of Earth-like planets contain a surprising amount of information about the spatial features of those worlds. Spatially resolving these light curves is important for assessing time-varying surface features and the existence of an atmosphere, which in turn is critical to life on Earth and significant for determining habitability on exoplanets. Given that Earth is the only celestial body confirmed to harbor life, treating it as a proxy exoplanet by analyzing time-resolved spectral images provides a benchmark in the search for habitable exoplanets. The Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) provides such an opportunity, with observations of ~5000 full-disk sunlit Earth images each year at 10 wavelengths with high temporal frequency. We disk-integrate these spectral images to create single-point light curves and decompose them into principal components (PCs). Using machine-learning techniques to relate the PCs to six preselected spatial features, we find that the first and fourth PCs of the single-point light curves, contributing ~83.23% of the light-curve variability, contain information about low and high clouds, respectively. Surface information relevant to the contrast between land and ocean reflectance is contained in the second PC, while individual land subtypes are not easily distinguishable (<0.1% total light-curve variation). We build an Earth model by systematically altering the spatial features to derive causal relationships to the PCs. This model can serve as a baseline for analyzing Earth-like exoplanets and guide wavelength selection and sampling strategies for future observations.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-3881/abd54aDOIArticle
https://arxiv.org/abs/2012.10556arXivDiscussion Paper
ORCID:
AuthorORCID
Gu, Lixiang0000-0002-3089-3706
Fan, Siteng0000-0002-3041-4680
Li, Jiazheng0000-0002-2563-6289
Bartlett, Stuart J.0000-0001-5680-476X
Natraj, Vijay0000-0003-3154-9429
Jiang, Jonathan H.0000-0002-5929-8951
Crisp, David0000-0002-4573-9998
Hu, Yongyun0000-0002-4003-4630
Tinetti, Giovanna0000-0001-6058-6654
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2021 The American Astronomical Society. Received 2020 September 3; revised 2020 December 10; accepted 2020 December 17; published 2021 February 16. L.G. and Y.H. are supported by the National Natural Science Foundation under grants 41530423, 41888101, and 41761144072. L.G. is also partly supported by the China Scholarship Council. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). D.C. and Y.L.Y. acknowledge support from the Virtual Planetary Laboratory at the University of Washington. Y.H. is also supported by the research project of Technology of Space Telescope Detecting Exoplanets and Life (D030201). G.T. was supported by the Science and Technology Funding Council of UK and UK Space Agency (ST/T001836/1, ST/V003380/1). J.H.J., S.J.B., and Y.L.Y. acknowledge funding support from the NASA Exoplanet Research Program NNH18ZDA001N-2XRP.
Funders:
Funding AgencyGrant Number
National Natural Science Foundation of China41530423
National Natural Science Foundation of China41888101
National Natural Science Foundation of China41761144072
China Scholarship CouncilUNSPECIFIED
NASA80NM0018D0004
NASA/JPL/CaltechUNSPECIFIED
University of WashingtonUNSPECIFIED
Technology of Space Telescope Detecting Exoplanets and LifeD030201
Science and Technology Facilities Council (STFC)ST/T001836/1
Science and Technology Facilities Council (STFC)ST/V003380/1
NASANNH18ZDA001N-2XRP
Subject Keywords:Exoplanet astronomy; Exoplanet atmospheres; Exoplanet surfaces; Exoplanets; Exoplanet structure; Exoplanet surface variability; Extrasolar rocky planets; Habitable planets; Exoplanet surface characteristics; Exoplanet atmospheric composition; Exoplanet atmospheric variability; Exoplanet surface composition
Issue or Number:3
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet astronomy (486); Exoplanet atmospheres (487); Exoplanet surfaces (2118); Exoplanets (498); Exoplanet structure (495); Exoplanet surface variability (2023); Extrasolar rocky planets (511); Habitable planets
Record Number:CaltechAUTHORS:20210223-090759375
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210223-090759375
Official Citation:Lixiang Gu et al 2021 AJ 161 122
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108150
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 Feb 2021 18:05
Last Modified:23 Feb 2021 18:05

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