Discovered15 September 2011Kepler, Doyle et al.[2]
About the image. Drawn as a cool, banded gas giant with its two suns, an orange dwarf and a smaller red dwarf, in the distance. The colours of the stars follow their temperatures; the cloud bands are imagined.
Kepler-16 is a pair of stars, an orange dwarf and a smaller red dwarf, that orbit each other every 41 days and eclipse each other as seen from Earth. In Kepler’s data, Laurance Doyle’s team noticed something else: dips in light at moments when neither star was in front of the other. Something was passing in front of them. On 15 September 2011 they announced Kepler-16b, the first planet confirmed beyond doubt to orbit two stars.
The Smithsonian astronomers involved nicknamed it Tatooine, after Luke Skywalker’s home world with its double sunset. Standing on a moon of Kepler-16b, if it had one, you would see two suns rise and set together, one orange and one red.
A planet in the wrong place
Kepler-16b is a gas giant about the size and mass of Saturn, cold at around −100 to −70 °C. It circles both stars every 229 days. It was a surprise to theorists, who expected a planet to need about seven times the distance between the two stars to form safely around a binary. Kepler-16b orbits at about half that. It probably formed farther out and migrated inward.
Because the planet crosses two stars, its transits pinned down its size very precisely: its radius is known to within 0.3 percent. When it was announced, Doyle called it the best-measured planet outside the Solar System. In 2021 it also became the first planet orbiting two stars to be detected by the wobble it gives its stars.
Gone from view until 2042
Its orbit slowly shifts. Kepler-16b stopped crossing the dimmer star in 2014 and the brighter one in 2018. No transits should be seen again until about 2042.
The planet sits near the outer edge of the system’s habitable zone. Life on a gas giant is unlikely, but simulations suggest an Earth-sized moon could have been captured, and a moon of at least 0.07 Earth masses could hold on to an atmosphere for billions of years. No such moon has been found.
Its orbit, to scale
Kepler-16b goes around once every 229 days, at 0.7048 AU from its star. Dashed circles show Mercury and Venus around the Sun, on the same scale.
Kepler-16b: equilibrium temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
Kepler-16b is about 245 light-years away.
Light299 792 km/s245 years
Breakthrough Starshotplanned light sail, 20% of light speed1 225 years
Parker Solar Probefastest spacecraft so far, 192 km/s382 547 years
Voyager 1leaving the Solar System, 17 km/s4.3 million years
At Voyager 1's speed the trip would take about 54 007 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Your weight on Kepler-16b
On Kepler-16b
Gravity there is about 1.48× Earth's, at the cloud tops; there is no surface. Calculated from the measured mass and radius.
Gallery
A pale, banded gas giant with two small orange stars at its left edge, an impression of Kepler-16b and its two suns. AI-generated painting.A pale icy plain under two suns, one setting on the horizon and a small red one high in the sky, an impression of the view from Kepler-16b. AI-generated painting.Kepler-16b, 3D artist's impression, rendered from the interactive model.Kepler-16b, 3D artist's impression, from another angle, rendered from the interactive model.Kepler-16b, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
2011Announced on 15 September as the first confirmed planet orbiting two stars.
2014Stops crossing the dimmer star.
2018Stops crossing the brighter star.
2021Detected from its pull on the stars, a first for a planet orbiting two suns.
Questions people ask
Is Kepler-16b like Tatooine?
Yes, in that it orbits two suns. Unlike Tatooine it is a cold gas giant the size of Saturn, not a desert world.
Could life exist on Kepler-16b?
On the gas giant itself it is very unlikely. A large moon, if it had one, could in theory hold an atmosphere.