Home → Exoplanets FAQ → How many Earth-like planets in the Milky Way Galaxy?
I have said that no Earth-like planets have been found so far, and I have also pointed out the difficulties with estimating the percentage of stars that host planets. However, despite these hurdles and the fact that we really have no idea how many planets are in our galaxy, some people have ventured so far as to estimate the number of habitable worlds in our Galaxy, the Milky Way. (Remember that we have actually only directly observed exoplanets in a tiny fraction of our Galaxy, so in addition to the physical uncertainties, a huge amount of extrapolation will is involved in such estimates.)
For an estimate of the possible number of habitable worlds in our Galaxy, we use the most conservative estimate of the percentage of sun-like stars that might harbor habitable planets from Catanzarite and Shao (2011) (taking the lower bound of the lowest number) of 0.4%. Then for the number of stars in the Milky Way we adopt the number 100 billion (again a conservative number). For the percentage of all stars that are sun-like, based on the criteria of Catanzarite and Shao (2011) and a census of the solar neighborhood, we adopt 23%. Multiplying all these together we get 92 million potentially habitable planets in the Milky Way. Even if this estimate is off by a factor of 1000, that would still be about 92000 planets. These are truly staggering and mind-boggling numbers.
Learn more about exoplanets with Exoplanets and Alien Solar Systems, which includes comprehensive references to the scientific literature.
File under: Earth-like planets in the Milky Way? Estimate of Habitable planets in our Galaxy.