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Astrophysics/How many habitable planets are in the Milky Way?


So I am working on worldbuilding a science fiction story and I need some consultation on how many habitable planets does the Milky Way contain?

Hi Antero,

I can give you a wild guess based on my estimates of total number of stars in the Milky Way (more than 100 billion), number of candidate stars - not too massive - usually considered in the G, K, and M spectral classes, number of stars with planets (probably greater than 50%), probability of planets of the proper composition and size (termed 'terrestrial planets'), etc. But some researchers have already done that! My favourite, from 2010, is here - Those researchers say "We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion... in the Milky Way".

So that's better than any answer I can give!


Prof. James Gort  


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James Gort


Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.


I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

StarDate, University of Texas, numerous Journal Publications

B.A. Physics and Astronomy M.Sc. Physics Ph.D. Astrophysics

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