The hunt for extra-terrestrials has expanded, after theoretical astrophysicists discovered that millions of planets once dismissed as inhospitable could in fact be suitable for alien life.

Earth-like planets are the obvious first place to look for life, but a large number of these orbit stars known as orange and red dwarfs, which are smaller than the Earth’s sun. Dwarf stars are extremely common—they make up more than 70% of stars in the universe—and nearly every red dwarf is thought to have a planet located within a habitable distance and with similar water levels to Earth.

But until recently, there’s been a catch—Earth-sized planets rotating dwarfs were thought to suffer from rotational lockup. That means they rotate with one side always facing the star, much like how one side of the Moon always faces the Earth. This would create a planet that was half scorching desert and half ice sheet, which is hardly ideal for life.

But research published in Science Express earlier this year found that this isn’t necessarily the case. The authors, led by Jérémy Leconte, a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics at the University of Toronto, built a three-dimensional climate model and found that a thin atmosphere would allow a planet to break free of rotational lockup and spin as it rotates around the star.

Scientists previously thought that only a large atmosphere could create a significant spin but, according to Leconte, thin atmospheres may have a larger rotational effect, because they allow more light from the star to reach the planet’s surface. This solar heat drives wind to create an atmospheric tide, which in turn creates a friction that causes the planet to rotate.

The researchers believe that an Earth-sized planet with an atmosphere similar to Earth’s would indeed spin as it rotates around small orange dwarf and some red dwarf stars. The astronomers are awaiting observational evidence to support their theory, but believe this could expand scientists’ search for life outside our solar system.

“If we are correct, there is no permanent, cold night side on exoplanets causing water to remain trapped in a gigantic ice sheet,” Leconte said in a statement. “Whether this new understanding of exoplanets’ climate increases the ability of these planets to develop life remains an open question.”