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Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography
Unmixing the disk-integrated spectra of exoplanets provides a clue to heterogeneous surfaces that we cannot directly resolve in the foreseeable future.
It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1.
We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.
Yuka Fujii, Jacob Lustig-Yaeger, Nicolas B. Cowan
(Submitted on 16 Aug 2017)
Comments: 11 pages, 7 figures; under review
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1708.04886 [astro-ph.EP] (or arXiv:1708.04886v1 [astro-ph.EP] for this version)
From: Yuka Fujii
[v1] Wed, 16 Aug 2017 13:27:51 GMT (3432kb,D)