A team of astronomers from NASA’s Goddard Space Flight Center in Greenbelt, Maryland and San Diego State University have found a new exoplanet, dubbed Kepler-1647b, roughly 3,700 light years away that is the largest circumbinary — or “Tatooine” planet — ever discovered.
A circumbinary planet is a planet that orbits two stars, much like Luke Skywalker’s home planet of Tatooine in Star Wars — hence the nickname. Discovering Tatooine planets isn’t easy, according to SDSU astronomer William Welsh, because their transits “are not regularly spaced in time and they can vary in duration and even depth.” Such was the problem with Kepler-1647b, which was initially believed to have been discovered back in 2011 by Laurance Doyle from the SETI institute, who first noticed the Tatooine planet’s transit. But much more data, and several years of analysis, was needed to confirm that Kepler-1647b was, in fact, a planet.
“Every 11 days the stars eclipse each other, so it is like a clock.”
The astronomers announced their discovery of the Tatooine planet in San Diego yesterday at the American Astronomical Society, and their research has been accepted for publication in the Astrophysical Journal.
The team used NASA’s Kepler Space Telescope to identify Kepler-1647b. Using data from the telescope, they search for slight dips in brightness around stars that would suggest a planet was in transit around, or passing in front of a star. Though normally Tatooine planets are difficult to find, Kepler-1647b was made more difficult by the fact that it’s orbital period is longer than most circumbinary planets, said SDSU astronomer Jerome Orosz, a coauthor on the study.
“It’s a bit curious that this biggest planet took so long to confirm, since it is easier to find big planets than small ones. But it is because its orbital period is so long.”
Kepler-1647b is approximately 4.4 million years old — roughly the same age as our Earth — and has a mass and radius nearly identical to Jupiter, making it the largest transiting Tatooine planet ever found. Its dual suns are even similar to ours, with one slightly larger, and the other slightly smaller. The planet’s orbit is 1,107 days — just over three years — an unusually long orbit for Tatooine planets, which are typically found much closer to their stars. What makes Kepler-1647b particularly interesting is the fact that its orbit puts it right in the so-called habitable zone — the range of distance from a planet’s star that makes for the perfect conditions for liquid water, not too hot, and not too cold.
While potential habitable moons is but one interesting bit of information surrounding Kepler-1647b, Welsh said it’s not the most important.
“Habitability aside, Kepler-1647b is important because it is the tip of the iceberg of a theoretically predicted population of large, long-period circumbinary planets.”
Though Kepler-1647b is the largest Tatooine planet found by the Kepler Space Telescope — launched in 2009 to look for habitable planets beyond our solar system — the discovery of circumbinary planets isn’t anything new. Kepler-1647b is the 11th Tatooine planet found in the seven years since the telescope’s initial launch.
[Image via NASA/Lynette Cook]