There Are 60 Billion Habitable Planets Littering the Milky Way

By Jamie Condliffe on at

A new study suggests that there are as many as 60 billion habitable planets orbiting red dwarf stars in the Milky Way alone—twice the number previously thought and strong evidence to hint that we may not be alone.

A team of scientists has been reassessing the limits of the habitable zones around red dwarf stars, which are smaller and fainter than the sun. Based on simulations of cloud behaviour on extrasolar planets—previously ignored in calculations—the team of astrophysicists calculated new parameters for defining a habitable zone around red dwarf stars. This cloud behavior dramatically expanded the size of the zone, as Dr. Dorian Abbot from the University of Chicago explains:

“Clouds cause warming, and they cause cooling on Earth. They reflect sunlight to cool things off, and they absorb infrared radiation from the surface to make a greenhouse effect. That’s part of what keeps the planet warm enough to sustain life."

The result? Instead of there being on average approximately one Earth-size planet in the habitable zone of each red dwarf, there are in fact roughly two. In total, that means there are around 60 billion habitable planets orbiting red dwarf stars in the Milky Way.

Interestingly, because red dwarf stars are relatively small and weak, the planets now deemed habitable would have to orbit their star's once every one to two months. In turn, they'd become tidally locked—which is where one side of the planet would always face the star, like one side of the moon always faces Earth. So, better pack a jumper or two if you want to visit the other side. [The Astrophysical Journal Letters via Sci News]