  Terrestrial planets in temperate orbits around very low mass stars are likely
to have evolved in a very different way than solar system planets, and in
particular Earth. However, because these are the first planets that are and
will be accessible for in-depth atmosphere, clouds and surface
characterizations with existing and forthcoming telescopes, we need to develop
the best possible observational strategies to maximize the scientific return
from these characterizations. Here I discuss and expand on the recent works of
Bean et al. (2017) and Turbet et al. (2019) to show that terrestrial planets
orbiting in temperate orbits around very low mass stars are potentially an
excellent sample of planets to test how universal the processes thought to
control the habitability of solar system planets and in particular Earth are.
Precise measurements of density or atmospheric CO2 concentration for planets
located both inside and outside the Habitable Zone could be used to
statistically test habitability concepts such as the silicate-weathering
feedback, CO2 condensation, or runaway greenhouse, which have been identified
as key processes controlling the present and past habitability of Venus, Mars
and Earth.
