Astronomers at SDSU and NASA announce discovery of large planet orbiting stars

SAN DIEGO (KUSI) — Astronomers at San Diego State University and NASA’s Goddard Space Flight Center announced Monday the discovery of the largest planet to orbit two stars.

Kepler-1647 b circles around the stars in the constellation Cygnus, around 3,700 light-years away.

The planet is around 4.4 billion years old, roughly the same age as the Earth, according to the scientists, who made their announcement on the second day of the American Astronomical Society’s 228th annual meeting at the Hilton San Diego Bayfront hotel.

Planets that orbit two stars are called circumbinary planets, or sometimes "Tatooine” planets, after Luke Skywalker’s homeland in "Star Wars.” Using NASA’s Kepler telescope, astronomers look for slight dips in brightness that hint a planet might be crossing the front of a star, blocking some of the star’s light.

"But finding circumbinary planets is much harder than finding planets around single stars,” said SDSU astronomer William Welsh, one of the paper’s co-authors. "The transits are not regularly spaced in time and they can vary in duration and even depth.”

It took researchers using advanced computer programs about five years to confirm the discovery.

According to the scientists, one of the stars is slightly larger than our sun and the other a bit smaller. The planet has a mass and radius nearly identical to that of Jupiter, making it the largest transiting circumbinary planet ever found, the researchers said.

"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,” said SDSU astronomer Jerome Orosz. "It took so long to confirm because its orbital period is so long.”

Kepler-1647 b takes around three of our years to orbit its host stars, the longest period of any confirmed transiting exoplanet found so far. The planet is also much farther away from its stars than any other circumbinary planet, breaking with the tendency for circumbinary planets to have close-in orbits.

While its orbit puts the planet within the so-called habitable zone, Kepler-1647 b is a gas giant like Jupiter, making it unlikely to host life, though any large moons could potentially be suitable for life.

"Habitability aside, Kepler-1647 b is important because it is the tip of the iceberg of a theoretically predicted population of large, long-period circumbinary planets,” Welsh said.

The research has been accepted for publication in the Astrophysical Journal with Veselin Kostov, a NASA Goddard postdoctoral fellow, as lead author.

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