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Found: planet the size of Jupiter orbiting two Sun-like stars

Lynette Cook

Researchers using data from NASA’s Kepler space telescope have spotted the largest planet yet orbiting a two-star system. The planet — dubbed Kepler-1647b — is basically the same size as Jupiter in terms of its radius and mass. The stars it orbits are also somewhat similar to our star: one is a bit bigger than the Sun, and the other is a bit smaller. The whole planetary system is located 3,700 light-years away and is thought to be 4.4 billion years old. That’s about the same age as our Solar System!

The largest known planet orbiting a two-star system

Kepler’s discovery was detailed today at a meeting of the American Astronomical Society in San Diego. Scientists identified the planet the same way most exoplanets are found: by measuring its transit. When planets regularly pass in front of their host star, they cause a slight dip in the star’s brightness that Kepler can detect from space. Scientists can figure out the size and mass of exoplanets by measuring these light dips, and determine the world’s orbital period by timing how long it takes for the dips to occur.

Planets orbiting dual star systems are extra hard to find, though. "The transits are not regularly spaced in time and they can vary in duration and even depth," William Welsh, a coauthor on the paper detailing the discovery and an astronomer at San Diego State University, said in a statement. Additionally, Kepler-1647b has an extra long orbital period, taking 1,107 days to travel once around the two stars. That’s the longest orbit of any known exoplanet. Kepler had to observe the star system for four years to witness multiple transits.

An artist rendering of Kepler-1647b. (Lynette Cook)

Another exciting aspect of the planet’s orbit is that it actually lies in the magical "habitable zone" of the two stars. That's the area where temperatures are just right for liquid water to exist on the surface of a rocky planet. And since water is so crucial for life here on Earth, its existence elsewhere in the Universe could also support extraterrestrial life. But there’s a hitch: Kepler-1647b is a gas giant, just like its long-lost twin Jupiter, so it probably doesn’t have any aliens. But if the planet does have a moon, that world could support water since it would also be in the habitable zone.

Kepler-1647b is just one of the latest amazing discoveries from Kepler, which has been studying exoplanets from space for more than seven years. Recently, NASA researchers confirmed 1,284 planets from data that the space telescope had gathered. So far, more than 2,000 verified exoplanets have been found thanks to Kepler data.

Correction June 13th, 3:28PM ET: A previous version of this article indicated the star system was 4.4 million years old. It's billions of years old, and the article has been updated.