A team of researchers has presented a new model of habitability within the Milky Way. According to their calculations, more than one in every hundred stars may have planets capable of supporting complex life within our Galaxy. Their results will be published in the journal Astrobiology.

Astronomers generally focus on exoplanets orbiting stars in the Galactic Habitable Zone (GHZ) when looking for planets that could support complex life. The GHZ has the shape of a donut: it is estimated to be 6,000 light-years thick and located 25,000 light-years away from the galactic center. This zone contains many stars similar to our Sun, containing high proportions of heavy elements: they are called metallic stars.

Michael Gowanlock from the University of Hawaii and colleagues wanted a more detailed study of habitability within our Galaxy, and examined various important factors. They took into account sterilised regions of the Galaxy caused by supernovae, and also included the time required for complex life to evolve. Finally, they considered habitability on tidally locked and non-tidally locked planets separately.

Taking all these factors into account (as well as a few others), they estimated that up to 1.2% of stars in our Galaxy could have planets with complex life. Knowing that there are between 200-400 billion stars in the Milky Way, that gives roughly 2.5 to 5 billion stars potentially having planets with complex life!

Another important detail is that there seems to be much more of these stars in the inner galaxy, about 2.7% of the stars in that region.


However, their model also predicts that about 75% of the planets orbiting these stars would be tidally locked: the same side is constantly facing their parent star, making it a burning hell, while the other side remains frozen in an everlasting night. Such planets would be uninhabitable.

Of course, there is still a lot of work to do, and the first habitable exoplanet will have to wait a long time before being discovered, and confirmed.  Many factors may influence habitability, and researchers are constantly improving their models. Thanks to studies like this one, astronomers know where to look and where Earth-like planets might be; and maybe someday, they will finally find another world much like our own.