# Comparative Climates of TRAPPIST-1 planetary system: results from a simple climate-vegetation model

## TL;DR

This study uses a simple climate-vegetation energy-balance model to analyze the potential habitability of TRAPPIST-1 planets, identifying conditions under which liquid water could exist and highlighting planet TRAPPIST-1d as the most stable candidate.

## Contribution

It introduces a simple climate-vegetation model to evaluate the habitability of TRAPPIST-1 planets, focusing on surface water potential under various conditions.

## Key findings

- TRAPPIST-1d is most likely to sustain liquid water.
- Outer planets f, g, h are unlikely to have surface liquid water.
- The model captures key climate features despite its simplicity.

## Abstract

The recent discovery of the planetary system hosted by the ultracool dwarf star TRAPPIST-1 could open new perspectives into the investigation of planetary climates of Earth-sized exoplanets, their atmospheres and their possible habitability. In this paper, we use a simple climate-vegetation energy-balance model to study the climate of the seven TRAPPIST-1 planets and the climate dependence on the global albedo, on the fraction of vegetation that could cover their surfaces and on the different greenhouse conditions. The model allows us to investigate whether liquid water could be maintained on the planetary surfaces (i.e., by defining a "surface water zone") in different planetary conditions, with or without the presence of greenhouse effect. It is shown that planet TRAPPIST-1d seems to be the most stable from an Earth-like perspective, since it resides in the surface water zone for a wide range of reasonable values of the model parameters. Moreover, according to the model outer planets (f, g and h) cannot host liquid water on their surfaces, even for Earth-like conditions, entering a snowball state. Although very simple, the model allows to extract the main features of the TRAPPIST-1 planetary climates.