Free Astronomy Magazine January-February 2015

6 ASTROBIOLOGY between 0.08 and 0.6, and it goes without saying that also the diameter will be consi- derably smaller. Why would stars so differ- ent from our own represent an ideal target in the search for extraterrestrial life? The reasons are many, but saying that on the whole it is almost a compulsory choice, is not far from reality. In fact, the two meth- ods offering the greatest chances of success in the discovery of other Earths, one based on transits and one on radial velocities, pro- vide the best results when applied to sys- tems consisting of a red dwarf with planets orbiting close to it; this because the transits are more frequent, the stellar dimming pro- portionately deeper, and the anomalies pro- duced by the planetary masses on the mo- tions of their stars more obvious. In order for an Earth-sized planet orbiting a red dwarf to present conditions suitable for life as we know it, it should be at a much smaller distance from its star than that between the Earth and the Sun (1 AU), more precisely at a distance that depending on the mass of the red dwarf goes from 0.1 to 0.5 AU. The possible negative aspects of such proximity had not always been ade- quately taken into account, such that red A rtist’s repre- sentation of a protoplanetary disk. These struc- tures give birth to stars and plan- ets at different rates depending on the masses in- volved. In the case of red dwarfs, the formation times are very long. [Subaru Telescope, NAO]