Habitable Zones

Polarized Signatures of Variable Worlds: Modeling Heterogeneous Habitable Earth- and Early Mars-like (Exo)planets

By Keith Cowing

Status Report

astro-ph.EP

September 23, 2025

Filed under astro-ph.EP, atmosphere, Biosignatures, Earth, exoplanet, habitability, Habitable Worlds Observatory, Habitable Zone, icy world, Mars, Ocean world, snowball earth

Polarized Signatures of Variable Worlds: Modeling Heterogeneous Habitable Earth- and Early Mars-like (Exo)planets — Surface (top row) and cloud (bottom row) distributions for our various Snowball Earth models. The surface was either modeled as a fully ice-covered “Hard Snowball” (top left) or contained a tropical ocean belt to simulate a “Slushball Earth” scenario (top right). Low-altitude water ice clouds (light blue) could have existed in an equatorial belt during summer months (bottom left) or only in the southern hemisphere during winter months. In winter these low-level clouds could have been fully covering the hemisphere (bottom middle left), scattered throughout the hemisphere (bottom middle right), or scattered throughout with additional high-altitude (grayish-blue) water ice clouds (bottom right). — astro-ph.EP

Determining the habitability of terrestrial exoplanets is a complex problem that represents the next major step for the astrophysical community.

The majority of current models treat these planets as homogeneous or contain heterogeneity that is constant in time. In reality, habitable exoplanets are expected to contain atmospheric and surface heterogeneities similar to Earth, with diurnal rotation, seasonal changes, and weather patterns resulting in complex, time-dependent signatures.

Due to its ability to measure light as a vector, polarimetry provides an important tool that will enhance the characterizations of heterogeneous worlds. Here we model the visible to near-infrared linear spectropolarimetric signatures, as functions of wavelength and planetary phase angle, of various heterogeneous Earth scenarios as well as the first signals of an early wet and potentially habitable Mars.

The contributions from the different atmospheric and surface properties result in asymmetric phase curves and variable spectra, with the polarization appearing to be more sensitive than flux to heterogeneities such as patchy clouds and continents moving into and out-of-view.

Our models provide important predictions of expected polarized and unpolarized signatures of heterogeneous exoplanets that will help guide the designs and observing plans of future polarimeters, including those proposed for the upcoming Habitable Worlds Observatory.

Kenneth E. Goodis Gordon, Theodora Karalidi, Kimberly M. Bott, Connor J. Vancil, Maxwell A. Millar-Blanchaer, Nicholas F. Wogan, Eric T. Wolf

Comments: 23 pages, 17 figures. Accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2509.16338 [astro-ph.EP] (or arXiv:2509.16338v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.16338
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Submission history
From: Kenneth Goodis Gordon
[v1] Fri, 19 Sep 2025 18:26:52 UTC (1,949 KB)
https://arxiv.org/abs/2509.16338

Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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