When a typical planet orbits a typical star, it stays confined within a flat oval like our own orbital path around the sun. Even in binary systems with two stars, a planet -- like, say, Tatooine from Star Wars -- probably traces the same kind of disk around one or both of its stars. But perhaps things aren’t so normal after all: The planet could be spiraling around an invisible axis as it bounces between the two stars, New Scientist reports.
Auburn University’s Eugene Oks developed a planetary model inspired by rare molecules known as one-electron Rydberg quasimolecules. Under electromagnetism, the orbits of their electrons are corkscrew-shaped, and Oks wondered if there might be planets out there that act the same way.
To understand Oks’s model, visualize a corkscrew that's held horizontally, and not vertically as if you were about to uncork a bottle of wine. First, you have to imagine a straight line connecting two stars, and then a planet tracing a corkscrew around that line. The planet travels from one star to the other and then back again along this strange orbit. (I find it easier to imagine a slinky for this next part.) As the planet moves closer to one star, the spirals get closer and closer together as the planet moves more slowly, New Scientist explains, until the planet turns and moves back toward the other star. In the middle, it traces wild, fast curves around the axis.
Oks looked to the binary stars of the Kepler-16 system (pictured above) to provide illustrative numerical data. Kepler-16b was the first planet known to orbit two stars; the so-called circumbinary planet was discovered by NASA’s Kepler mission back in 2011. Viewed from Earth, the pair of orbiting stars occasionally block each other: When the smaller one partially obstructs the larger one, you get a primary eclipse, and a second eclipse occurs when the larger one completely blocks out the smaller one. When astronomers were observing the Kepler-16 system, they noticed that the brightness sometimes dipped even when the stars were not eclipsing each other. That’s when they discovered a third body, the Saturn-sized world of Kepler-16b.
Astronomers don’t know whether Kepler-16b follows the corkscrew orbit that Oks proposes; he just wanted to show that such worlds are possible. If these hypothetical planets with what are called stable conic-helical orbits do exist, they’d be bizarre places. Only a small section of the planet would ever experience nighttime, and the seasons would come and go quickly.
"I'm delighted at the likelihood that somewhere in our vast universe there surely must be some screwball planets like these in binary star systems," says UC Berkeley’s Geoff Marcy, who wasn’t involved with the study. "What a discovery -- wacky but undoubtedly true!"
The findings were published in The Astrophysical Journal last week.
1
