The UniverseAnswer
What Is the Higgs Field, and Why Call Its Particle the “God Particle”?
An everywhere-present field, a fleeting particle and a famous nickname. What did CERN’s experiments actually measure?
THE QUESTION LIBRARY THE UNIVERSE
Can a Planet Orbit Two Stars?
Two stars can circle each other while a planet travels around them both. Astronomers confirmed it by watching the moving stars dim.
THE SHORT ANSWER
Yes. A planet can follow a wide orbit around a pair of stars while the stars orbit each other. Astronomers call it a circumbinary planet. Kepler-16 b takes about 229 Earth days to go around both stars, which circle each other about every 41 days. On an imagined rocky world with that arrangement, two suns could set one after the other.
- Some planets orbit both stars of a binary.
- The Kepler-16 stars circle in about 41 days, and the planet takes about 229 days.
- Astronomers observed transits across both stars and later detected the planet independently through stellar motion.
- The Kepler-47 binary has three known planets.
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About this picture
Original AI-generated illustration for God Plays Dice, imagining two suns setting over the horizon of a rocky circumbinary world.
WHERE THE EVIDENCE STANDS
How sure are we?
- Kepler-16 b orbits both of its host stars.Transits across both stars and later measurements of the brighter star’s motion support the orbit.
- A pair of stars can host multiple circumbinary planets.Three transiting planets have been identified in the Kepler-47 system.
- How common are circumbinary planets across different kinds of binary stars?Different viewing angles and orbital periods affect how many surveys can detect.
WHAT WE DON’T KNOW YET
How common these planets are is harder to measure than their existence. Detectability varies with orbital alignment, observation time, and the way the stars and planet move.
WHAT WOULD CHANGE THIS ANSWER
Longer surveys and measurements of systems viewed from different angles would sharpen estimates of how common circumbinary planets are.
Imagine one sun slipping below the horizon while another still lights the landscape. That view is possible on a world that orbits a pair of stars. In one real system, the stars complete more than five laps around each other during a single planetary year.
THE LONG ANSWER
Free long answer 3 of 3 this month.
How can one planet orbit two stars?
The two stars orbit a shared balance point called their center of mass. The planet travels on a much wider path that encloses both stars. From far enough away, their combined gravity acts roughly like the pull of a single mass at that balance point. Closer in, the changing positions of the two stars can matter much more.
A planet in a binary system can also orbit just one of the stars. When it stays close to one member of a widely separated pair, that star can dominate its motion. The word circumbinary describes the arrangement where the planet goes around both.
How did astronomers find Kepler-16 b?
From Earth’s direction, the two stars sometimes pass in front of each other. Their combined light dips during these eclipses. The Kepler-16 discovery team also saw extra dips caused by a planet crossing in front of each star at different times. The timing helped reveal the planet’s path. Because the stars themselves were moving, each crossing depended on where the planet and the star met along our line of sight.
In the resulting model, the stars orbit each other in about 41 days and the planet completes a circuit in about 229 days. A later study using changes in the brighter star’s motion (PDF) independently detected the planet and measured its mass. The Library’s guide to finding exoplanets explains how astronomers use changes in light and stellar motion.
Does the planet stay in a stable orbit?
Some paths can last a long time. In computer simulations of planets around binary stars, a planet’s chances of staying on its orbit depended on details such as how stretched the stars’ orbit was and how their masses compared. A wider orbit can help keep a planet away from the strongest variations in the stars’ pull. The simulations followed specified systems for a finite time, so they give a guide to where stability is likely.
Some pairs can even host several planets. Observations of the Kepler-47 system revealed three planets that orbit the same pair of stars.
Could you actually see two sunsets?
On a rotating rocky world with two suns, both could be visible in the same sky and could set at different times. The view would change with where the stars were in their orbits and where you stood. NASA describes Kepler-16 b as a gas giant, so the illustration imagines a different world.
Keep asking
How do astronomers find planets around other stars?
Astronomers often find exoplanets by measuring a small, repeating dip in a star’s light when a planet crosses in front of it, or by detecting the star’s slight…
New here?
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (3)
- Binary star
- A pair of stars bound by gravity that orbit a shared center of mass.
- Circumbinary planet
- A planet whose orbit takes it around both stars of a binary.
- Transit
- A crossing in front of a star, as seen by an observer, that can briefly reduce the star’s apparent brightness.
Sources & further reading
(3) · Checked Nov 8, 2026
- Kepler-16: A Transiting Circumbinary Planet ↗Science · author manuscript on arXivOriginal discovery, with transits across both stars.
- Long-Term Stability of Planets in Binary Systems ↗The Astronomical Journal · author manuscript on arXivNumerical experiments on where planetary orbits can survive around one star or both.
- Discovery of a Third Transiting Planet in the Kepler-47 Circumbinary System ↗The Astronomical Journal · author manuscript on arXivObservations of three planets circling the same pair of stars.
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