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