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Global Mapping of an Exo-Earth Using Sparse Modeling

Aizawa, Masataka and Kawahara, Hajime and Fan, Siteng (2020) Global Mapping of an Exo-Earth Using Sparse Modeling. Astrophysical Journal, 896 (1). Art. No. 22. ISSN 1538-4357. doi:10.3847/1538-4357/ab8d30.

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We develop a new retrieval scheme for obtaining two-dimensional surface maps of exoplanets from scattered light curves. In our scheme, the combination of the L1-norm and total squared variation, which is one of the techniques used in sparse modeling, is adopted to find the optimal map. We apply the new method to simulated scattered light curves of the Earth, and find that the new method provides a better spatial resolution of the reconstructed map than those using Tikhonov regularization. We also apply the new method to observed scattered light curves of the Earth obtained during the two-year Deep Space Climate Observatory/Earth Polychromatic Imaging Camera observations presented by Fan et al. The method with Tikhonov regularization enables us to resolve North America, Africa, Eurasia, and Antarctica. In addition to that, the sparse modeling identifies South America and Australia, although it fails to find Antarctica, maybe due to low observational weights on the poles. Besides, the proposed method is capable of retrieving maps from noise-injected light curves of a hypothetical Earthlike exoplanet at 5 pc with a noise level expected from coronagraphic images from a 8 m space telescope. We find that the sparse modeling resolves Australia, Afro-Eurasia, North America, and South America using 2 yr observation with a time interval of one month. Our study shows that the combination of sparse modeling and multiepoch observation with 1 day or 5 days per month can be used to identify main features of an Earth analog in future direct-imaging missions such as the Large UV/Optical/IR Surveyor.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Aizawa, Masataka0000-0001-8877-4497
Kawahara, Hajime0000-0003-3309-9134
Fan, Siteng0000-0002-3041-4680
Additional Information:© 2020 The American Astronomical Society. Received 2019 October 23; revised 2020 April 24; accepted 2020 April 24; published 2020 June 9. The authors thank the DSCOVR team for making the data publicly available. We also thank Yasushi Suto and Shiro Ikeda for fruitful discussions on sparse modeling and its application for mapping, and we thank Yuk L. Yung for discussions on surface map retrieval using DSCOVR observations. This work is supported by JSPS KAKENHI Grant Nos. 14J07182 (M.A.), JP17K14246, JP18H04577, JP18H01247, and JP20H00170 (H.K.). M.A. is also supported by the Advanced Leading Graduate Course for Photon Science (ALPS) and by the JSPS fellowship. This work was also supported by the JSPS Core-to-Core Program "Planet2" and SATELLITE Research from Astrobiology center (AB022006).
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)14J07182
Japan Society for the Promotion of Science (JSPS)JP17K14246
Japan Society for the Promotion of Science (JSPS)JP18H04577
Japan Society for the Promotion of Science (JSPS)JP18H01247
Japan Society for the Promotion of Science (JSPS)JP20H00170
Advanced Leading Graduate Course for Photon Science (ALPS)UNSPECIFIED
SATELLITE Research from Astrobiology centerAB022006
Subject Keywords:Exoplanet astronomy ; Astrobiology ; Direct imaging
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet astronomy (486); Astrobiology (74); Direct imaging (387)
Record Number:CaltechAUTHORS:20200609-133710696
Persistent URL:
Official Citation:Masataka Aizawa et al 2020 ApJ 896 22
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103800
Deposited By: Tony Diaz
Deposited On:09 Jun 2020 21:06
Last Modified:16 Nov 2021 18:25

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