For years, planets orbiting two stars have seemed more like science fiction than reality.
The most famous example is probably Tatooine, the desert world from Star Wars with its iconic double sunsets.
But scientists are now finding that these strange worlds may be far more common than once believed.
A new study led by researchers at UNSW Sydney has identified 27 possible circumbinary planets—planets that orbit two stars instead of one. The discovery dramatically expands the number of known candidates and could change how astronomers search for planets across the galaxy.
The findings were published in the Monthly Notices of the Royal Astronomical Society.
Until now, scientists had confirmed only 18 circumbinary planets, compared to more than 6,000 known planets orbiting single stars like our own sun. Researchers say that imbalance may not reflect reality. Instead, it may simply be a result of the methods scientists have traditionally used to search for planets.
“Most of our current knowledge on planets is biased, based on how we’ve looked for them,” says Margo Thornton, the study’s lead author. “We’ve mostly found the easiest ones to detect.”
Most exoplanets are discovered using something called the transit method. This happens when a planet passes in front of its star from Earth’s point of view, causing a tiny dip in the star’s brightness. While highly successful, this method only works if the planet’s orbit lines up perfectly with our line of sight.
That means many planets may remain invisible to us simply because they orbit at different angles.
To overcome this problem, Thornton and her team used a different technique called apsidal precession. Instead of searching for planetary shadows, the method looks for subtle changes in how two stars orbit each other.
Binary stars regularly eclipse one another, creating predictable patterns of light. But if the timing of those eclipses shifts slightly, it may mean a third object—possibly a planet—is gravitationally tugging on the stars.
The researchers used data from NASA’s Transiting Exoplanet Survey Satellite, also known as TESS, to analyze 1,590 binary star systems.
To their surprise, the team quickly found 27 strong planet candidates.
“I wasn’t expecting to find 27 already at this point from the pilot study,” says Ben Montet, senior author of the study.
The candidate planets vary greatly in size. Some may be as small as Neptune, while others could be up to 10 times the mass of Jupiter.
The closest candidate system is around 650 light-years from Earth, while the farthest is about 18,000 light-years away. Even so, the researchers say these systems are still part of our broader galactic neighborhood.
The planets are currently considered “candidates” because scientists still need additional observations to confirm whether they are truly planets or perhaps larger objects such as brown dwarfs or faint stars.
Researchers are now using the Anglo-Australian Telescope to study the stars more closely and rule out other explanations.
The discovery may only be the beginning. The team estimates that around 2% of binary star systems could host planets. Since more than half the stars in the universe belong to binary or multiple-star systems, there may be thousands—or even tens of thousands—of these worlds waiting to be discovered.
Scientists are especially excited because some of these planets could potentially support life.
“If circumbinary planets do turn out to be habitable, that means life could be anywhere,” says Montet. “Life could be everywhere.”
For Thornton, the search is about more than just finding planets. It is also about understanding humanity’s place in the universe.
“We just want to understand where we came from,” she says, “and what else exists out there.”
