Kepler-1647b: The Largest ‘Tatooine’ Planet With 2 Suns Discovered


Graphic showing Kepler-1647b's size compared to that of all other two-star planets discovered by NASA's Kepler space telescope to date. (Image: Lynette Cook)

Using the Kepler Space Telescope, a team of astronomers from NASA’s Goddard Space Flight Center and San Diego State University (SDSU) were able to identify the new planet Kepler-1647b. Planets that orbit two stars are called circumbinary planets; however, some call them “Tatooine” planets, after Luke Skywalker’s homeland in Star Wars.

To discover planets, astronomers look for slight dips in brightness, which indicate a planet may be transiting in front of a star, blocking some of the star’s light. NASA’s Kepler telescope has been instrumental in this process.

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Kepler-1647b with two host stars.
Artist’s illustration of the newfound exoplanet Kepler-1647b crossing the face of one of its two host stars. (Image: via Lynette Cook)

William Welsh, an astronomer from San Diego State University and one of the paper’s co-authors, said in a statement:

“But finding circumbinary planets is much harder than finding planets around single stars.

“The transits are not regularly spaced in time and they can vary in duration and even depth.”

After astronomers find a candidate, advanced computer programs are then used to determine if it really is a planet. Laurance Doyle, an astronomer from the SETI Institute and also a co-author on the paper, was the first to notice a transit in 2011. However, to confirm the transit was caused by a circumbinary planet, astronomers needed more data and several years of analysis before they could make the confirmation.

Kepler-1647b’s estimated mass

A network of amateur astronomers in the KELT Follow-Up Network also provided additional observations, which helped researchers to estimate the planet’s mass. Kepler-1647b is approximately 4.4 billion years old, which is roughly the same age as the Earth, and sits 3,700 light-years away. The planet stars are similar to our sun, although one is slightly larger, and the other is slightly smaller.

Kepler-1647b's orbit.
The orbits of all previously known circumbinary planets are shown as gray circles. Kepler-1647 b’s much larger orbit is the red circle. (Image: B. Quarles via Univ. Oklahoma)

SDSU astronomer Jerome Orosz, another co-author on the study, 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.

“It took so long to confirm because its orbital period is so long.”

The giant takes 1,107 days (a little over 3 years) to orbit its host stars, making it the longest period of all confirmed exoplanets. Kepler-1647b is also much further away from its stars than any other circumbinary planet (circumbinary planets have a tendency to have close-in orbits).

This puts the exoplanet within the so-called habitable zone; however, because Kepler-1647b is a gas giant, it is unlikely to host any life. “Yet if the planet has large moons, they could potentially be suitable for life,” SDSU wrote.

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