Terrestrial planets are common in the Milky Way. It has been estimated, in fact, that at least 30% of stars in the Solar neighborhood host a terrestrial planet, and this fraction increases to 40% considering the habitable zone around all M stars (e.g. stars with effective temperature between 2400 and 3700 degrees) of the Galaxy. The habitable zone is defined
To date (October 2019), 4073 exoplanets have been confirmed, while 4495 are still candidates. The vast majority of these exoplanets have been discovered with two techniques: the analysis of transits (e.g.: measuring the decline of stellar luminosity during the passage of the planets in across the stellar disk) and radial velocity (by detecting, thanks to the Doppler effect and spectroscopic
