Small exoplanets orbiting small stars are the most common outcome of planet formation. Their occurrence is so high, in fact, that the closest rocky planets in the habitable zone of their parent stars might well be “around the corner” in astronomical terms, as the recent discovery of Proxima Cen b demonstrates.
Terrestrial exoplanets orbiting stars cooler and less massive than the Sun will be the prime targets for atmospheric characterization and the search of potential biomarkers in the near future. This because the planet/star signal ratio is sensibly increased compared to an Earth-Sun twin.
In this talk I will present a relatively recent and novel technique to observe exoplanet atmospheres based on the use of high dispersion spectroscopy (HDS). I will review past successes in characterizing giant planets, among which are the first detections of the atmospheres of non-transiting planets and the first measurements of exoplanet rotation. I will show how HDS will be used in the near future to characterize hundreds of exoplanets, including those found by TESS, and eventually combined with high-contrast imaging to hunt for biomarkers, with a particular focus on terrestrial planets orbiting M-dwarfs such as Proxima Cen b.