Astronomers calculate there could be billions of stars in the Milky Way galaxy that may have one to three “Goldilocks” planets each in the habitable zone, the region around a star that makes it just right for life to potentially exist on a planet.

Using the NASA’s Kepler satellite, astronomers have confirmed about 1,000 planets around stars in the Milky Way and 3,000 potential planets, to date. The Kepler satellite discovers exoplanets by observing if the light curve of a star shows a reoccurring small dip in brightness, indicating a planet obscuring its light as it orbits its host.

To estimate how many of these systems have planets in the habitable zone, researchers from the Australian National University and the Niels Bohr Institute made calculations based on an updated version of the 250-year-old the Titius-Bode law.

Comparative Life Zones of Stars. Credit: NASA/Kepler Mission/Dana Berry.

The theory states that there is a ratio between the orbital periods of planets in a solar system. Historically, it has had both success and failures in predicting the orbits of planetary bodies in our own solar system.

The scientists placed the already observed planets into the ‘pattern’ for where they should be located and slotted in others that seemed to be missing between the known planets as determine by the Titius-Bode law. One extra planet in the system beyond the outermost known planet was also added.

Using the theory, the researchers then proposed that there were a total of 228 planets across the 151 planetary systems, with each system hosting one to three planets in the habitable zone. They made a priority list with 77 planets in 40 planetary systems to further study to give more weight to their research.

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“According to the statistics and the indications we have, a good share of the planets in the habitable zone will be solid planets where there might be liquid water and where life could exist,” Steffen Kjær Jacobsen, PhD student at the Niels Bohr Institute.

The research published in the Monthly Notices of the Royal Astronomical Society states: “If you then take the calculations further out into space, it would mean that just in our galaxy, the Milky Way, there could be billions of stars with planets in the habitable zone, where there could be liquid water and where life could exist.”

Habitable zones differ in each system as they are relative to the size and brightness of the host star. Planets that orbit close around a star are too hot to have liquid water and planets that are far from the star would be too deep-frozen to support life, while the intermediate habitable zone is thought to be just right for liquid water and to support life.

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However, there are known exceptions to the rule. Scientists recently announced a discovery about Saturn’s sixth-largest moon, Enceladus, which sits well outside of our own solar system’s habitable zone.

Data from NASA's Cassini spacecraft allowed scientists to confirm that the ice moon’s south pole resemble the deep oceans on Eart h with a heated ocean exhibiting ongoing hydrothermal activity. As Enceladus is too far from the sun for to provide energy-giving heat, the hydrothermal activity within its oceans provides the third believed element needed to support life.

Jenna Pitcher is a freelance journalist writing for IGN. You can follow her on Twitter