Exoplanetology: Exoplanets & Exomoons

Earth As An Exoplanet: Investigating The Effects Of Cloud Variability On The Direct-imaging Of Atmospheres

By Keith Cowing
Status Report
astro-ph.EP
March 13, 2025
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Earth As An Exoplanet: Investigating The Effects Of Cloud Variability On The Direct-imaging Of Atmospheres
The top panel shows the different rotational configurations of the exo-Earth labeled by a rotational phase. These images only depict how the portion of the surface visible to the observer changes with rotation and don’t imply that the planet is cloudless. The plots show the reflected light spectra for the different rotational phases as simulated by PSG for a cloudy and a cloud-free exo-Earth respectively. The entire wavelength bandpass is seperated into three regions – (i) ultraviolet (UV) (0.2-0.5 µm), (ii) visible (VIS) (0.5-1 µm) and (iii) near-infrared (NIR) (1-2 µm). The simulated error bars have been removed for the sake of visual clarity. The cloudy planet shows a higher continuum in the reflected light which is attributed to the enhanced albedo in the presence of clouds. The spectrum of a cloudy planet also shows a higher degree of variation between rotational phases due to variable cloud patchiness. — astro-ph.EP

A planet’s spectrum is dynamic and only represents a time-dependent snapshot of its properties. Changing atmospheric conditions due to climate and weather patterns, particularly variation in cloud cover, can significantly affect the spectrum in ways that complicate the understanding of a planet’s baseline atmospheric properties.

Variable cloud cover and cloud properties affect the detectability of atmospheric constituents, and also greatly influence the radiative transfer that determines a planet’s spectrum. This has considerable implications for direct imaging observations of potentially habitable exoplanets and thus it is critical to study and characterize the effects of clouds on their spectra.

Clouds have been extensively modeled before and their effects have been incorporated across climate frameworks spanning a spectrum of complexity. Given the challenges associated with modeling clouds, we adopt a novel approach in this work to study the effects of clouds by using real-time cloud data from Earth observations.

Treating Earth as an exoplanet and using detailed observations from the MERRA 2 data collection, we quantify the effects of cloud variability on the spectrum as well as on the detectability of atmospheric constituents, specifically biomarkers like O2, O3 and H2O. The coverage and vertical position of clouds significantly affects the SNRs of these gases and subsequently their detectability in exo-Earth atmospheres.

Moreover, we show that variations in the amount of cloud cover will potentially confound efforts to retrieve a stable baseline atmosphere for a planet. This work has important applications to future direct-imaging missions like the Habitable Worlds Observatory (HWO).
Soumil Kelkar, Prabal Saxena, Ravi Kopparapu, Joy Monteiro

Comments: Accepted for publication in PSJ, 21 pages, 7 figures, Zenodo link for attached config files – this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2503.09136 [astro-ph.EP] (or arXiv:2503.09136v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2503.09136
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Submission history
From: Soumil Kelkar
[v1] Wed, 12 Mar 2025 07:57:40 UTC (1,976 KB)
https://arxiv.org/abs/2503.09136
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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