Free Astronomy Magazine September-October 2019

6 SEPTEMBER-OCTOBER 2019 With all the research programs focused on identifying potentially habitable or inhab- ited planets, the overall goal was to search indiscriminately around stars of very differ- ent sizes, leaving out, at most, those of the first spectral types O, B and A, due to the fact that their brief stay on the main sequence does not give enough time for any planets around them to become definitely habitable. It is reasonable to suppose that the longer a star remains on the main sequence, the higher the probability that an orbiting Earth- like planet can host life forms. The smaller the initial mass of a star, the longer its per- manence on the main sequence, so it goes without saying that M dwarfs present them- selves as a rather interesting target, not only because their average life greatly exceeds the current age of the universe, but also be- cause they are the most common stars in the galaxy, representing at least 75% of the total stellar population. Furthermore, if we consider that M dwarfs’ weak surface brightness and small mass favor the discovery of planets both with the transit method and the radial velocity variation method, it is no surprise that the largest F or a long time considered ideal stars around which to look for biosignatures, red dwarfs are instead proving increasingly unsuitable be- cause of the vio- lent flares that characterize them and that interact with their plane- tary atmos- pheres. Above, we see a repre- sentation of it. On the left, plan- etary systems comparison. On TRAPPIST-1 plan- ets, many hopes were placed which are now fading. [NASA/ JPL-Caltech]