The Outer Edge Of The Venus Zone Around Main-Sequence Stars

By Keith Cowing
April 26, 2022
Filed under
The Outer Edge Of The Venus Zone Around Main-Sequence Stars
A comparison of CO2 condensation zones for our various Venus analogs. Solid bold bands indicate where CO2 is condensed within the atmosphere of a given Venus analog. For a 3000 K M star, CO2 begins condensing in our Venus analog at 0.3 Seff, and for a 3400 K M star, CO2 begins condensing at 0.32 Seff. For a G star, CO2 begins condensing in our Venus analog atmosphere at 0.55 Seff, whereas a Venus analog around a K star and an F star begins CO2 condensation at 0.38 and 0.8 Seff, respectively. For M and K star profiles, CO2 condensation occurs lower in the atmosphere compared to F and G stars. As noted in Figure 1, the N2 in our Venus analogs is effective at scattering blue light that is most present in F and G stars, while CO2 is effective at absorbing light in the infrared that is most present in M and K stars, therefore maintaining heat and additionally allowing heat to be maintained to the surface.

A key item of interest for planetary scientists and astronomers is the habitable zone, or the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface.

However, when observing a system’s habitable zone, it is possible that one may instead observe a Venus-like planet.

We define “Venus-like” as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end-state of evolution for habitable worlds, requires an improved understanding of the Venus-like planet; specifically, the distances where these planets can exist.

Understanding this helps us define a “Venus zone”, or the region in which Venus-like planets could exist, and assess the overlap with the aforementioned “Habitable Zone”. In this study, we use a 1D radiative-convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types.

Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 AU, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.

Monica R. Vidaurri, Sandra T. Bastelberger, Eric T. Wolf, Shawn Domagal-Goldman, Ravi Kumar Kopparapu

Comments: Accepted for publication in the Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2204.10919 [astro-ph.EP] (or arXiv:2204.10919v1 [astro-ph.EP] for this version)
Submission history
From: Monica Vidaurri
[v1] Fri, 22 Apr 2022 20:19:20 UTC (646 KB)


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