Habitability of Red Dwarf Systems

Determining the habitability of red dwarf systems could help reveal the likelihood of extraterrestrial life, as red dwarfs make up most stars in the Milky Way Galaxy. While the relatively little energy output, small habitable zones, probability of tidally locked planets, and high stellar variation are postulated impediments to habitability, the ubiquity and longevity of red dwarfs are possible positive factors.

As of 2012, many factors appear to indicate that many red dwarfs, smaller than 30% of Sun's mass, have a very low probability for hosting indigenous life. Planets in the habitable zone of most red dwarfs would experience such a strong tidal heating that the hydrogen necessary for water and all known life would be 'baked out' of the planets before a stable orbit could be achieved, creating so-called 'Tidal Venuses'. Combined with other problems, such as those created by tidal locking, the variable radiation of red dwarfs, lack of planetary axial tilts, small habitable zones due to low energy output, different spectral energy distribution than the Sun (lacking ultraviolet and visible light), etc., this would indicate that the probability of red dwarf stars hosting life as we know it is very low compared to other star types. However, this does not mean that the planets around red dwarfs are 'uninhabitable' (could not be inhabited by future humans or other non-indigenous life).

A recent estimate put the number of Earth-sized planets in the habitable zones of red dwarf stars in our galaxy to number in the tens of billions. So although very improbable, the sheer number of red dwarf planets might overcome the limitations of red dwarf systems, and further scientific research and insights into astrobiology may also increase the odds of finding life around M-class stars.