Global Mapping of an Exo-Earth Using Sparse Modeling

Aizawa, Masataka; Kawahara, Hajime; Fan, Siteng

doi:10.3847/1538-4357/ab8d30

Cited by 21 publications

(26 citation statements)

References 34 publications

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“…Fan et al (2019) demonstrated that information about the surface is contained in the second principal component (PC) of the single-point light curves, and recovered a surface map in the presence of interference from clouds. Further improvements were made by Aizawa et al (2020) by comparing different regularization methods. This technique can serve as a standard surface mapping strategy for future exoplanet studies (Fan & Yung 2020).…”

Section: Introductionmentioning

confidence: 99%

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

Fan

et al. 2021

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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 singlepoint 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.

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Section: Introductionmentioning

confidence: 99%

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

Fan

et al. 2021

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“…Numerous authors have proposed innovative uses of DISCOVR data to consider Earth as an exoplanet. 14,15,[25][26][27][28][29][30][31][32] EarthShine will collect observations of Earth from space at illumination phases not yet observed (Fig. 5), with a consistent set of instruments, simultaneously spanning wavelength ranges of interest (Fig.…”

Section: Earthshine In Contextmentioning

confidence: 99%

EarthShine: Observing our world as an exoplanet from the surface of the Moon

Boyd

Wilson

Smale

et al. 2022

J. Astron. Telesc. Instrum. Syst.

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NASA's return to the Moon coincides with explosive growth in exoplanet discovery.Missions are being formulated to search for habitable planets orbiting other stars, making this the ideal time to deploy an instrument suite to the lunar surface to help us recognize a habitable exoplanet when we see it. We present EarthShine, a technically mature, three-instrument suite to observe the whole Earth from the Moon as an exoplanet proxy. EarthShine data will validate and improve models critical for designing missions to image and characterize exoplanets, thus informing observing strategies for flagship missions to directly image exoplanets. EarthShine will answer interconnected questions in Earth and lunar science, exoplanets, and astrobiology, related to the credo "follow the water." EarthShine can take advantage of current NASA programs to conduct science from the Moon with low-cost, mature space hardware to reduce risk and assure success. Like the 1968 Apollo Earthrise image of our home planet, lonely in the black sky, the appeal of EarthShine to a multidisciplinary array of researchers in Earth Science, Planetary Science, and astrophysics will maximize both its scientific impact and its impact on the general public.

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“…Although the planetary obliquity and rotation rate have not yet been made clear from observations yet, future observations should provide sufficient information to establish these parameters (Kawahara, 2012(Kawahara, , 2016Nakagawa et al, 2020). Theoretical studies regarding the mapping of planetary surfaces have also been proposed (Aizawa et al, 2020;Fujii et al, 2010;Kawahara, 2020). In the next generation of studies on exoplanets, it should be possible to distinguish between an aqua planet and a land planet from observations.…”

Section: Exoplanetsmentioning

confidence: 99%

The Onset of a Globally Ice‐Covered State for a Land Planet

et al. 2021

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A number of potentially habitable exoplanets located within the habitable zone of their host star have been detected. The habitable zone, which is defined as the region around a star where liquid water on a planetary surface remains stable, is the most widely used concept in exoplanetary science, as it helps narrow the search for oceans beyond Earth (e.g., Kasting et al., 1993;Kopparapu et al., 2013Kopparapu et al., , 2014. In the next decade, planets within the habitable zone will be primary candidates for observation of their biosignature.The edges of the classical habitable zone have been estimated for an aqua planet that is globally covered with ocean using a one-dimensional radiative-convective model. Recently, one can address the climate for terrestrial potential habitable planets and their habitability using three-dimensional general circulation models (GCMs). GCM studies have produced examples of climates for potentially habitable planets -for example, Proxima Centauri b and the Trappist-1 planets (Turbet et al., 2016(Turbet et al., , 2018(Turbet et al., , 2020.There are two definitions of the inner edge of the habitable zone: the runaway greenhouse limit and the moist greenhouse limit (e.g., Kasting et al., 1993;Kopparapu et al., 2013). From 1D radiative-convective equilibrium models, we know that a planet with a wet atmosphere has a limit on planetary radiation, called the Simpson-Nakajima limit, due to an atmospheric structure whereby the temperature profile asymptotically approaches the saturated vapor pressure curve for water vapor, leading to constant planetary radiation at the position where the optical depth equals unity (Ingersoll, 1969;Nakajima, Hayashi & Abe, 1992). When such a planet receives insolation

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Global Mapping of an Exo-Earth Using Sparse Modeling

Cited by 21 publications

References 34 publications

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

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

EarthShine: Observing our world as an exoplanet from the surface of the Moon

The Onset of a Globally Ice‐Covered State for a Land Planet

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