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Long after 'Star Wars,' real-life Tatooine discovered

DULUTH - Evocative. Soul-stirring. Who can forget the moment Luke Skywalker walks from his igloo-abode, kicks the sand in frustration and then stops to watch the sunset from his home planet Tatooine in "Star Wars." This is no ordinary sunset. We ...

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This real-life Tatooine orbits much closer to its binary suns than is considered possible. In the gravitational chop created by the dual suns revolving about their common center of gravity, planets have to keep a safe distance to remain in stable orbits. BrainerdDispatch.com Illustration

DULUTH - Evocative. Soul-stirring. Who can forget the moment Luke Skywalker walks from his igloo-abode, kicks the sand in frustration and then stops to watch the sunset from his home planet Tatooine in "Star Wars." This is no ordinary sunset. We look out across the desert landscape at twin suns -- one white, one yellow -- in one of the most alien and yet believable scenes ever incorporated into a movie. The camera focuses on Luke's moody gaze in the slanting light. The music swells. His expression changes. In that moment, Luke realizes there's more to life than farming for moisture on Tatooine. His destiny lies in greater things ... somewhere in a galaxy far, far away.

When that scene from "Episode IV -- A New Hope" was filmed in the mid-1970s, Pluto was still a planet, and not a single extrasolar planet had been discovered. Now we know of more than 2,011 planets that orbit stars other than the sun. Of that number, only 19 are circumbinary planets, the term astronomers use to describe a planet that orbits two suns, as the fictional Tatooine does.

The first confirmed, unambiguous example of this special class of planets, Kepler-16 (AB) b, was discovered in the constellation Cygnus the Swan 200 light years from Earth on Sept. 15, 2011, by the orbiting Kepler Space Telescope. Kepler looks for repeating dips in a star's light when a planet transits or passes in front of the star. By measuring how much the planet dims its host star's light, astronomers can determine its size and orbit.

In the case of the Kepler planet, astronomers were able to measure its mass by watching how the planet causes changes in the times of the two stars eclipsing one another. Only a very slight gravitational pull was detected, one that only could be caused by a small mass.

At 66,000 miles across and a third as massive as Jupiter, Kepler-16 (AB) b is similar to Saturn with a climate that bears little resemblance to the brutal if survivable heat of Tatooine. It orbits 64.6 million miles from its twin suns once every 229 days at the outer edge of the binary's habitable zone, where liquid water could exist on its surface. While that distance is similar to Venus' distance from the sun, the parent stars, Kepler AB, are both smaller and fainter than our sun.

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Kepler-16 (AB) b is a cold "gas giant" -- a planet heavy on atmosphere with a small, rocky core -- with a surface temperature between 50 and 94 degrees below zero. Positively Antarctic.

But the planet's most amazing attribute is that it's there at all. This real-life Tatooine orbits much closer to its binary suns than is considered possible. In the gravitational chop created by the dual suns revolving about their common center of gravity, planets have to keep a safe distance to remain in stable orbits.

It was once thought that any circumbinary planets had to orbit at least seven times as far from the stars as the stars are from each other. Kepler 16-b orbits at just half that distance.

Scientists have turned up newer Tatooines since 2011, including Kepler-453b, discovered earlier this year. It's the 10th circumbinary planet found by the Kepler Mission, and a gas giant some 49,000 miles across or 60 percent bigger than Neptune.

The more the merrier. Finding planets around double suns puts a positive spin on prospects for life on exoplanets given that 85 percent of stars in the Milky Way are believed to be binaries. Once thought to be a difficult environment for a planet to survive, double-sun worlds may be as common as single stars like our sun.

Tatooine may be hot, lawless and overrun by Hutt gangsters, but it was there that Luke aspired to more. Perhaps astronomers will find a real Tatooine someday, one that aspired to the formation of life, the real power behind the Force.

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By Bob King, Forum News Service

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