Climate Modeling of a Potential ExoVenus

TL;DR

This study models the atmospheric evolution of Kepler-1649b, a potential exoVenus, showing it likely undergoes a runaway greenhouse effect, and discusses how future telescopes could detect such states.

Contribution

It applies a general circulation model to simulate atmospheric evolution of Kepler-1649b and assesses the detectability of its runaway greenhouse signatures with JWST.

Findings

Kepler-1649b's atmosphere rapidly diverges to a runaway greenhouse state.

Simulated transmission spectra reveal detectable atmospheric signatures.

Future telescopes like JWST can identify Venus-like atmospheric conditions.

Abstract

The planetary mass and radius sensitivity of exoplanet discovery capabilities has reached into the terrestrial regime. The focus of such investigations is to search within the Habitable Zone where a modern Earth-like atmosphere may be a viable comparison. However, the detection bias of the transit and radial velocity methods lies close to the host star where the received flux at the planet may push the atmosphere into a runaway greenhouse state. One such exoplanet discovery, Kepler-1649b, receives a similar flux from its star as modern Venus does from the Sun, and so was categorized as a possible exoVenus. Here we discuss the planetary parameters of Kepler-1649b with relation to Venus to establish its potential as a Venus analog. We utilize the general circulation model ROCKE-3D to simulate the evolution of the surface temperature of Kepler-1649b under various assumptions, including relative atmospheric abundances. We show that in all our simulations the atmospheric model rapidly diverges from temperate surface conditions towards a runaway greenhouse with rapidly escalating surface temperatures. We calculate transmission spectra for the evolved atmosphere and discuss these spectra within the context of the James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) capabilities. We thus demonstrate the detectability of the key atmospheric signatures of possible runaway greenhouse transition states and outline the future prospects of characterizing potential Venus analogs.