Scientists officially call them circumbinary planets, but even they can’t help but dub them ‘Tatooine’ planets. The latest ‘Tatooine’ planet discovered is also the largest found orbiting a pair of stars. This is Kepler-1647b.
A comparison image showing how Kepler-1647b stacks up against other known circumbinary planets.
Astronomers from NASA’s Goddard Space Flight Center and San Diego State University (SDSU) spotted the massive world 3,700 light-years away from Earth. Obviously, we can’t see it with the naked eye, but head outside tonight and look towards the constellation Cygnus. It’s nestled in there.
So, what do we know about Kepler-1647b and its stars? Astronomers estimate it’s around the same age as Earth at 4.4 billion years old. And while the planet is large, its stars are pretty normal. One of them is a little larger than our sun, while the other is a little smaller.
As for the planet itself? Imagine a world with the mass and radius of Jupiter. That should have made it easier to spot, right? Not so fast. SDSU astronomer William Welsh explains why ‘Tatooine’ worlds are harder to spot than worlds around a single star.
“But finding circumbinary planets is much harder than finding planets around single stars,” said Welsh. “The transits are not regularly spaced in time and they can vary in duration and even depth.”
Did You Know: You don’t need a massive telescope to detect far-flung planets. Kepler had a little help from the appropriately named Kilodegree Extremely Little Telescope, or KELT. There are two of theses in the world. One in Arizona. The other in South Africa. Each night it takes images of thousands of stars looking for small dips in brightness. With the help of this small telescope (seen below) astronomers were able to estimate the mass for Kepler-1647b.
Credit: Vanderbilt University
Another challenge was Kepler-1647b’s orbital period. Using Kepler, astronomers tend to find planets with close orbital periods. Shorter time between transits means faster confirmation of a planet. Kepler-1647b takes more than three years (1,107 days) to complete one orbit.
This planet marks the first time a ‘Tatooine’ planet has been detected so far away from its star pair. All the planets orbiting two stars discovered so far tend to be much closer to their host stars. Here’s a graphic comparing Kepler-1647b’s orbit (red) with similar planets. Earth’s orbit is shown in blue.
Because it sits in a binary system, Kepler-1647b resides inside the habitable zone (where liquid water can pool on the surface). While the planet probably doesn’t host life (it’s a gas giant), any moons orbiting it could.
The Kepler mission continues to march forward. And with the full backing of NASA. The space agency recently announced Kepler will continue its search for planets through the end of the 2019 fiscal year. After that, its supply of onboard fuel is expected to run out.
Look for that number of confirmed exoplanets to keep heading higher over the next two years and beyond.