A one-dimensional energy balance model parameterization for the formation of CO2 ice on the surfaces of eccentric extrasolar planets

Venkatesan, V. and Shields, A.L. and Deitrick, R. and Wolf, A.T. and Rushby, Andrew (2025) A one-dimensional energy balance model parameterization for the formation of CO2 ice on the surfaces of eccentric extrasolar planets. Astrobiology 25 (1), pp. 42-59. ISSN 1531-1074.

Abstract

Eccentric planets may spend a significant portion of their orbits at large distances from their host stars, where low temperatures can cause atmospheric CO2 to condense out onto the surface, similar to the polar ice caps on Mars.The radiative effects on the climates of these planets throughout their orbits would depend on the wavelength-dependent albedo of surface CO2 ice that may accumulate at or near apoastron and vary according to the spectralenergy distribution of the host star. To explore these possible effects, we incorporated a CO2 ice-albedo parame-terization into a one-dimensional energy balance climate model. With the inclusion of this parameterization, oursimulations demonstrated that F-dwarf planets require 29% more orbit-averaged flux to thaw out of global waterice cover compared with simulations that solely use a traditional pure water ice-albedo parameterization. Whenno eccentricity is assumed, and host stars are varied, F-dwarf planets with higher bond albedos relative to theirM-dwarf planet counterparts require 30% more orbit-averaged flux to exit a water snowball state. Additionally,the intense heat experienced at periastron aids eccentric planets in exiting a snowball state with a smaller increasein instellation compared with planets on circular orbits; this enables eccentric planets to exhibit warmer conditionsalong a broad range of instellation. This study emphasizes the significance of incorporating an albedo parameter-ization for the formation of CO2 ice into climate models to accurately assess the habitability of eccentric planets,as we show that, even at moderate eccentricities, planets with Earth-like atmospheres can reach surface tempera-tures cold enough for the condensation of CO2 onto their surfaces, as can planets receiving low amounts of instel-lation on circular orbits. Vidya https://orcid.org/0000-0002-5638-4344 vidyav1@uci.edu, Aomawa L. Shields, Russell Deitrick, Eric T. Wolf, and Andrew Rushby

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