Imagine finishing outdoor work as the light fades, only to watch the sky brighten again — a second sun climbing the horizon where the first one just set. It’s a disorienting reality that exists somewhere out there, on worlds that orbit not one star but two.
Astronomers call them circumbinary planets, and they’re genuinely difficult to find. Now, an international team has announced 27 new candidates orbiting binary star systems in data from NASA’s TESS spacecraft — identified through a technique that had never been applied to this kind of search before.
Planets with two suns: rarer and harder to find than you’d think
Circumbinary planets orbit both stars in a two-star system simultaneously — a gravitationally complex arrangement that makes them compelling targets for researchers. Scientists are drawn to them partly because they raise fundamental questions about planetary formation: can stable worlds coalesce in environments where the gravitational landscape is constantly shifting? And if they can, could any of them support conditions for life?
Finding these worlds is no simple task. The transit method — which measures the dip in starlight when a planet passes in front of its host — requires the planet to align with both stars at once to register a detectable signal. That geometric constraint sharply limits how often a circumbinary planet reveals itself, which is why only 18 have been confirmed to date.
A new technique born from gravitational physics
The new study introduces a different approach: apsidal precession. When a planet orbits a binary pair, its gravitational influence causes the shape of the stars’ mutual orbit to gradually twist over time. That twisting leaves a measurable signature in the timing of stellar eclipses — and crucially, it doesn’t require the planet to be crossing in front of either star at the moment of observation. By sidestepping the alignment problem entirely, the method opens a much wider window for detection.
The research team applied this technique to 1,590 eclipsing binary stars already known to exhibit apsidal precession in TESS data. Lead author Margo Thornton, a PhD candidate at the University of New South Wales in Sydney, explained the motivation directly. “Identifying transits in binary systems clearly is challenging, but we’d like to know more about the range of planets that can form around two gravitationally bound stars,” she said. “So, we developed a survey to search for planets using stellar eclipses that is not limited to the orientation of the planet’s orbit.”
27 candidates that could more than double what we know
The headline result: 27 new circumbinary planet candidates identified from the TESS dataset. The word “candidate” carries real weight here — physical properties like planetary size remain inconclusive, and these worlds haven’t yet cleared the bar required for formal confirmation.
Still, the number is notable. If even a significant fraction of these 27 are eventually confirmed, they would more than double the current total of 18 confirmed circumbinary planets — a meaningful expansion of a catalog that has grown slowly for years. The path to confirmation likely runs through the radial velocity method, a well-established technique that detects the gravitational wobble a planet induces in its host stars. Follow-up observations using that approach could help determine which candidates hold up under closer scrutiny.
TESS and the legacy of planet-hunting missions
TESS launched in April 2018 as the designated successor to NASA’s Kepler mission and its follow-up K2 mission. Kepler stared at a single patch of sky for years, confirming more than 3,300 exoplanets over roughly 9.5 years of operation. TESS took a different approach — an all-sky survey designed to cast a far wider net.
So far, TESS has confirmed 855 exoplanets, with more than 7,900 additional candidates awaiting follow-up. The confirmed count trails Kepler’s, but the breadth of sky coverage gives TESS a structural advantage for searches that depend on rare configurations — like binary star systems already showing apsidal precession. That coverage is precisely what made this study possible. The research was published in the Monthly Notices of the Royal Astronomical Society.
What comes next for binary-star planet hunting
The deeper significance of this work may lie less in the 27 candidates themselves and more in what the method represents. A detection approach unconstrained by transit alignment is, in principle, faster and more broadly applicable than the transit method for this class of planets. Applied to larger datasets, it could accelerate the pace of circumbinary planet discovery considerably.
Confirmation will take time — likely years of follow-up observation. But each candidate that holds up adds to a census that remains frustratingly small given how common binary star systems are throughout the galaxy.
The habitability question lingers in the background. Can worlds orbiting two stars maintain the stable conditions life might require? The answer depends partly on having enough confirmed examples to study in detail, which makes an expanded known population a necessary first step. Future missions and ground-based observatories will have more data to work with, and the apsidal precession method gives researchers a new tool to bring to all of it.