  With thousands of exoplanets now identified, the characterization of
habitable planets and the potential identification of inhabited ones is a major
challenge for the coming decades. We review the current working definition of
habitable planets, the upcoming observational prospects for their
characterization and present an innovative approach to assess habitability and
inhabitation. This integrated method couples for the first time the atmosphere
and the interior modeling with the biological activity based on ecosystem
modeling. We review here the first applications of the method to asses the
likelihood and impact of methanogenesis for Enceladus, primitive Earth, and
primitive Mars. Informed by these applications for solar system situations
where habitability and inhabitation is questionned, we show how the method can
be used to inform the design of future space observatories by considering
habitability and inhabitation of Earth-like exoplanets around sun-like stars.
