Global Mapping of the Surface Composition on an Exo-Earth using Color Variability

Abstract

Photometric variation of a directly imaged planet contains information on both the geography and spectra of the planetary surface. We propose a novel technique that disentangles the spatial and spectral information from the multi-band reflected light curve. This will enable us to compose a two-dimensional map of the surface composition of a planet with no prior assumption on the individual spectra, except for the number of independent surface components. We solve the unified inverse problem of the spin-orbit tomography and spectral unmixing by generalizing the non-negative matrix factorization (NMF) using a simplex volume minimization method. We evaluated our method on a toy cloudless Earth and observed that the new method could accurately retrieve the geography and unmix spectral components. Furthermore, our method is also applied to the real-color variability of the Earth as observed by Deep Space Climate Observatory (DSCOVR). The retrieved map explicitly depicts the actual geography of the Earth and unmixed spectra capture features of the ocean, continents, and clouds. It should be noted that, the two unmixed spectra consisting of the reproduced continents resemble those of soil and vegetation.

20 pages, 14 figures, accepted for publication in ApJ. The code is available online at https://github.com/HajimeKawahara/sot. updated to match the published version

References in corpus (5)

• Alien Maps of an Ocean-Bearing World
• Identifying the rotation rate and the presence of dynamic weather on extrasolar Earth-like planets from photometric observations
• Global Mapping of Earth-like Exoplanets from Scattered Light Curves
• Detecting Ocean Glint on Exoplanets Using Multiphase Mapping
• Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography

Cited by in corpus (6)

• Global Mapping of an Exo-Earth using Sparse Modeling
• Earth as a Proxy Exoplanet: Deconstructing and Reconstructing Spectrophotometric Light Curves
• Bayesian Dynamic Mapping of an Exo-Earth from Photometric Variability
• Measuring the variability of directly imaged exoplanets using vector Apodizing Phase Plates combined with ground-based differential spectrophotometry
• Planet cartography with neural learned regularization
• Global Mapping of Surface Composition on an Exo-Earth Using Sparse Modeling