Extrasolar Planets

Global Mapping of Surface Composition on an Exo-Earth Using Sparse Modeling

By Keith Cowing
astro-ph.EP
April 6, 2022
Filed under
Global Mapping of Surface Composition on an Exo-Earth Using Sparse Modeling
(a)–(c) Input surface distributions and (d)(e)(f)(m) inferred solutions by spin-orbit unmixing with `1-norm and TSV regularization using a cloudless Earth model, (g)(h)(i)(n) trace norm regularization, and (j)(k)(l)(o) Tikhonov regularization. The first, second, and third columns of (a)–(l) are vegetation, land, and ocean distributions, respectively. In spectra (m)–(o), the solid lines is the inferred spectra and the dotted lines represents the input spectra. (j), (k), (l), and (o) are based on Kawahara (2020).

The time series of light reflected from exoplanets by future direct imaging can provide spatial information with respect to the planetary surface.

We apply sparse modeling to the retrieval method that disentangles the spatial and spectral information from multi-band reflected light curves termed as spin-orbit unmixing. We use the ℓ1-norm and the Total Squared Variation norm as regularization terms for the surface distribution. Applying our technique to a toy model of cloudless Earth, we show that our method can infer sparse and continuous surface distributions and also unmixed spectra without prior knowledge of the planet surface. We also apply the technique to the real Earth data as observed by DSCOVR/EPIC.

We determined the representative components that can be interpreted as cloud and ocean. Additionally, we found two components that resembled the distribution of land. One of the components captures the Sahara Desert, and the other roughly corresponds to vegetation although their spectra are still contaminated by clouds. Sparse modeling significantly improves the geographic retrieval, in particular, of cloud and leads to higher resolutions for other components when compared with spin-orbit unmixing using Tikhonov regularization.

Atsuki Kuwata, Hajime Kawahara, Masataka Aizawa, Takayuki Kotani, Motohide Tamura

Comments: 26 pages, 10 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2204.01996 [astro-ph.EP] (or arXiv:2204.01996v1 [astro-ph.EP] for this version)
Submission history
From: Atsuki Kuwata
[v1] Tue, 5 Apr 2022 05:30:07 UTC (10,297 KB)
https://arxiv.org/abs/2204.01996
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