The Effect of Land Albedo on the Climate of Land-Dominated Planets in the TRAPPIST-1 System

TL;DR

This study uses climate modeling to show how land surface albedo and composition significantly influence the climate of land-dominated exoplanets orbiting TRAPPIST-1, highlighting the importance of surface properties in climate predictions.

Contribution

It introduces a detailed analysis of land surface composition and albedo effects on exoplanet climate using empirical spectra and the CESM model, specific to TRAPPIST-1 planets.

Findings

Higher albedo materials increase surface temperature differences.

Land composition affects atmospheric circulation and heat transport.

Aquaplanet scenario leads to runaway greenhouse effect.

Abstract

Variations in the reflective properties of the bulk material that comprises the surface of land-dominated planets will affect the planetary energy balance by interacting differently with incident radiation from the host star. Furthermore, low-mass cool stars, such as nearby M8V dwarf TRAPPIST-1, emit a significant fraction of their flux in longer wavelengths relative to the Sun in regions where terrestrial materials may exhibit additional variability in albedo. Using the Community Earth System Model (CESM) we investigate the effect of the composition of the land surface and its albedo on planetary climate in the context of spatially homogeneous, entirely land-covered planets with dry atmospheres at the orbital separation of TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f. We use empirically derived spectra of four terrestrial compositional endmembers (granite, calcite, aridisol, and dune sand) and a composite spectrum of TRAPPIST-1 for these simulations and compare these model output to an aquaplanet and several Sol-spectrum control cases. We report a difference of approximately 50 K in global mean surface temperature, variations in atmospheric rotational features, and a reduction in cross-equatorial heat transport between scenarios in which materials with higher albedo in the infrared (calcite and dune sand) were used and those with more absorptive crustal material, such as granite or dry soils. An aquaplanet TRAPPIST-1d scenario results in an unstable runaway greenhouse regime. Therefore, we demonstrate that determining the composition and albedo of continental landmasses is crucial for making accurate determinations of the climate of terrestrial exoplanets.