Geochemical attainability of high atmospheric CO2 inventories

Determine whether the atmospheric CO2 inventories considered for planets orbiting the Sun or TRAPPIST-1 are geochemically attainable and can be sustained over geological timescales, in order to establish the true extent of the outer habitable zone for each planetary system.

Background

The study derives outer habitable-zone boundaries using anoxic, CO2-dominated atmospheres with prescribed CO2 partial pressures. These calculations establish climatic behavior for specified atmospheric inventories but do not model the coupled evolution of planetary interiors, atmospheric outgassing, and weathering processes that determine whether such inventories can exist and persist over geological timescales.

Resolving this question requires coupled geochemical–climate modeling. The answer would determine whether the modeled high-CO2 climates are physically realizable and, consequently, whether the calculated outer habitable-zone boundaries represent attainable planetary states rather than only radiative-climate limits.

References

While this study explores a range of CO2 partial pressures, it does not determine whether those CO2 inventories are geochemically attainable for planets orbiting the Sun or TRAPPIST-1. Coupled geochemical and climate modeling will therefore be required to determine which atmospheric CO2 abundances can be sustained over geologic timescales and, consequently, to establish the true extent of the OHZ for a given planetary system.

— High-CO2 Climates and Observables in the Outer Habitable Zone  (2609.36697 - Pidhorodetska et al., 29 Sep 2026) in Section 4.2, subsection “Planetary Parameters”