One of the most iconic scenes in Star Wars was of the two setting suns over Tatooine's dusty plains. Now, after years of searching, we've discovered that such a vista could exist outside science fiction. Scientists at NASA today announced the discovery of what they're describing as the very first confirmed, unambiguous example of a "circumbinary planet," orbiting not one, but two stars — just like Tatooine.
Meet Kepler-16b (K-16b). See those two blazing balls of gas in the video? Those are K-16b's twin suns. The larger of the two is roughly 69% the mass of our Sun, while the smaller, red star is closer to 20% of our Sun's mass.
The trio was recently discovered going about its business some 200 light years away by NASA's exoplanet-hunting Kepler Space Telescope. According to astronomer Laurance Doyle, who led the Kepler team that first observed the planetary system, the planet is half rock and half gas; comparable to Saturn in both size and mass; and experiences temperatures in the range of -100 to -150 F, "kind of like a nippy day on Mars."
"We don't expect anything like Luke Skywalker to be living on K-16b," quipped Nick Gautier, a Kepler project scientist from NASA's Jet Propulsion Laboratory, during a press conference held earlier this afternoon. "But if you were to visit you would see two suns just like Luke did."
And the planet's twin suns would be quite a sight to behold. Kepler-16b orbits its parent stars every 229 days, but the stars themselves orbit one another every 41 days. The astronomers don't know anything about K-16b's rotation period, so they're not sure about the frequency of the planet's sunrises and sunsets, but they do know that the irregularity of the system's multiple orbits probably makes for some absolutely jaw-dropping sights.
"Sometimes the red sun would set first, sometimes they'd set touching each other, sometimes they'd set at the same time; it's a very dynamic sunset — no two would be the same," explained Doyle. "You'd have, of course, two shadows — but If you wanted to tell the time by them, you'd probably need calculus."
The planet's unique relationship with its binary star system is what led the Kepler team to the discovery. Over the last several years, the Kepler mission has observed hundreds of examples of what are known as "eclipsing binary" systems, wherein two orbiting stars take turns eclipsing one another relative to the Kepler telescope's line of sight. Every time one star eclipses the other, it results in a temporary decrease in the stars' combined brightness. Eventually, a pattern of dimming and brightening called a "light curve" emerges, like the one featured here (via).
But the readouts for Kepler-16b's eclipsing binary were different. "We kept seeing extra dips in the light curve," recalls Doyle. The team didn't know it at first, but the extra dips were coming from none other than K-16b, which kept passing in between the orbiting stars and Kepler's line of sight, mucking with the characteristic dips in brightness that the team is accustomed to seeing from eclipsing binaries.
After an extensive analysis of the curious light curve and the duration of each dimming period — the details of which are published today in the journal Science — Doyle's team concluded that the only possible explanation for the pattern was a planetary system comprising two closely-orbiting suns that were, in turn, orbited by a planetary body — that is to say by K-16b (check the video for a high-definition, overhead depiction of the planetary system).
"This particular planet is far enough away from the two stars that it's effectively feeling them [from a gravitational standpoint] like one star" explains Astrophysicist Greg Laughlin, a professor of astronomy at UC Santa Cruz. "This planet should be able to orbit for many billions of years to come without encountering any significant difficulties."
"There's no indication [K-16b] is going to go unstable," echoed Doyle. And it's a good thing, too. According to him, K-16b will serve as a brand new experimental "laboratory" for about half a dozen astrophysical fields, ranging from stellar formation to stellar modelling:
When we find [new systems like K-16b], it allows us to calibrate all our previously-known systems...This is an example of another planetary system, a planetary system of a completely different type than any we've ever seen before. That's why everybody is so excited.
The feeling of excitement was one shared by all the interviewees at today's press conference, which included John Knoll, the visual effects supervisor for Industrial Light and Magic.
"When I was a kid I never imagined that it would be possible to make discoveries like this," said Knoll. "K-16b is unambiguous and dramatic proof that planets really do form around binaries; it's possible that there's a real Tatooine out there, that a planet like that really exist."
"I think I speak for everybody," resonated Laughlin, "when I say that it's been remarkable that the whole Kepler team has brought these exotic environments that used to exist only in science fiction firmly into the realm of science fact."
Top image and videos via NASA/JPL-Caltech