Researchers said that the Milky Way galaxy may hold between one and three exoplanets, or planets orbiting stars beyond our own solar system, that could potentially support life. Their conclusions appeared in the scientific journal Monthly Notices of the Royal Astronomical Society on Wednesday.

Astronomers discovered this by calculating the chances of planets orbiting in the “habitable zone,” or the region a certain distance from the parent star that could host watery oceans and mild temperatures. Planets that are too close to the star are too hot to support life and planets too far from the star would be deeply frozen.

Steffen Kjaer Jacobsen, Danish researcher from the University of Copenhagen, said that based on their research, a “good share” of planets in the habitable zone could allow for “liquid water.” He added that “life could exist” on those solid planets.

Their results come from NASA’s Kepler space telescope, which was launched in 2009 in search of exoplanets. The satellite discovered 1,000 planets around stars in the Milky Way, and they discovered 3,000 other potential planets.  Several stars have two to six planets, but it is possible they have more beyond the eye of the Kepler satellite.

In order to estimate the number of planets not picked up by the satellite, researchers updated and used a 250-year-old mathematical concept called Titius-Bode Law. This was the law that questioned the existence of Uranus before it was discovered, according to the Huffington Post.

According to the Titius-Bode Law, a particular ratio between the orbital periods of planets in a solar system exists. So, if the astronomers know the length of some planets’ orbits around the stars, then they can determine the positions and orbital periods of other planets. They can also determine if a planet is missing in a sequence.

Jacobsen said they decided to use this method to calculate potential positions in planetary systems where the “Kepler satellite had found between three and six planets.” He added that the law fit with the positions of planets in 124 planetary systems.

However, the team only made calculations for planets that have a “good chance” of being observed by the Kepler satellite. The scientists made a list of 77 “hidden” planets that could be spotted when they pass by their parent stars.

Scientists estimated a total of 228 planets in 151 systems. They concluded that each system could obtain one to three planets in the habitable zone. This conclusion suggested that billions of stars in the Milky Way could have planets where life could exist.