Scientists researching nine binary star systems—like our Solar System but with two Suns—have revealed that five have “habitable zones” that could host Earth-like planets.

Binary stars were made famous in Star Wars when Luke Skywalker watched a double sunset on Tatooine. So far the only exoplanets found in binary star systems have been giant gas planets.

Published in Frontiers in Astronomy and Space Sciences, a newly developed mathematical framework allowed researchers at New York University Abu Dhabi and the University of Washington to tease-out the existence of habitable zones in these binary star systems, where they’re not expected to exist.

Contrary to what was believed, the presence of giant planets in binary star systems does not appear to preclude the existence of potentially life-supporting rocky planets.

“Our study confirms that even binary star systems with giant planets are hot targets in the search for Earth 2.0,” said corresponding author Dr Nikolaos Georgakarakos, a research associate from the Division of Science at New York University Abu Dhabi. “Watch out Tatooine, we are coming!”

The five binary star systems that host life

Found in the constellations of Lyra and Cygnus by NASA’s Kepler Space Telescope during its 2009-2018 mission to survey the Milky Way, the five systems—all binary stars systems except one, which is bizarre quadruple system—have for the first time been shown to have permanent habitable zones around them.

All have at least one giant planet the size of Neptune or greater in orbit. They are:

  • Kepler-34: two Sun-like stars 6,200 light-years away in Cygnus.
  • Kepler-35: two Sun-like stars 6,300 light-years away in Cygnus.
  • Kepler-38: a Sun-like star and a much smaller star 3,970 light-years away in Lyra.
  • Kepler-64: a quadruple star system with stars orbiting one another at its center, 4,892 light-years away in Cygnus.
  • Kepler-413: a K-type star 2,764 light-years in Cygnus.

The ‘best’ planet: Kepler-38

Among the star systems examined Kepler-35, Kepler-38, and Kepler-64 appear to offer the most benign environment, but one stands out. “Our best candidate for hosting a world that is potentially habitable is the binary system Kepler-38, approximately 3,970 light years from Earth, and known to contain a Neptune-sized planet,” said Georgakarakos.

What are binary star systems?

Just like Tatooine in Star Wars, planets have been found in binary stars systems, some of which even orbit both stars. Of the 2,662 exoplanets found by the Kepler Space Telescope during its mission, only 12 orbit a close pair of stars, but such star systems are thought to be in the majority.

However, until now only giant exoplanets have been discovered in binary systems, probably because smaller planets—like Earth—are very tricky to find.

It was thought that multi-star systems that contain giant Neptune-sized planets would make it harder for rocky Earth-like planets to survive in stable “quiet” orbits.

“We’ve known for a while that binary star systems without giant planets have the potential to harbor habitable worlds,” said coauthor Prof. Ian Dobbs-Dixon of New York University Abu Dhabi. “What we have shown here is that in a large fraction of those systems Earth-like planets can remain habitable even in the presence of giant planets.”

The importance of the ‘habitable zone’

It’s a region around stars in which liquid water could persist on the surface of any as yet undiscovered Earth-like planets and, therefore, life.

“Life is far most likely to evolve on planets located within their system’s habitable zone, just like Earth,” said Georgakarakos. “We show for the first time that Kepler-34, -35, -64, -413 and especially Kepler-38 are suitable for hosting Earth-like worlds with oceans.”

In the other binary systems they studied, the immense gravity of giant planets in those systems would destabilize the orbits of any planets. Planets that are pushed into elliptical orbits may swing in and out of a star’s habitable zone, freezing and thawing and generally making permanent liquid water impossible.

“Of course, there is the possibility that life exists outside the habitable zone or on moons orbiting the giant planets themselves,” said coauthor Dr Siegfried Eggl at the University of Washington. “But that may be less desirable real-estate for us.”

More proof that looking for life0sustaining exoplanets is much like house-hunting—it’s all about location, location, location.

Wishing you clear skies and wide eyes.