Previously, six other planets had been found circling double stars, but "this is the first planet discovered in a four-star system," Yale planetary astronomer Megan Schwamb said Monday at a meeting of the American Astronomical Society's Division for Planetary Sciences in Reno, Nevada.
PH1, which is about 6.2 times Earth's width, orbits two of the stars, which are themselves orbited by a second pair.
One of the primary stars is superbright and 1.7 times larger than our sun. The other is dimmer and is only 41 percent the width of our sun. PH1 circles these two at about two-thirds the distance of Earth from our sun.
The other stars are far, far away—approximately 30 times the distance between Neptune and our sun. From that range, the stars would simply appear as a pair of brilliant pinpoints.
But don't expect that sunset scene in Star Wars: None of the four suns would be visible from the planet's surface.
That's because PH1 is a gas giant—about half as massive as Jupiter—and its surface would be shrouded with thick clouds, which would make seeing stars difficult.
Even if there were a cloudless atmosphere, Schwamb added, the light from a nearby superbright star would likely make stargazing impossible on PH1.
Odd Planet a Milestone
The odd planetary system is a milestone for a few reasons. For one, it challenges conventional notions of how planets form, Schwamb said.
"The discovery of these systems is forcing us to go back to the drawing board to understand how such planets can assemble and evolve in these dynamically challenging environments," she said in a statement.
What's more, PH1 is also the first planet found by participants in the Planet Hunters project, a collaboration of Yale University and the Zooniverse, a website that supports citizen science.
As part of that program, amateur scientists scan data from NASA's Kepler Space Telescope, looking for the tiny variations in starlight that occur when planets pass between us and their host stars.
Such planets can be tricky to spot in multiple star systems, Schwamb said, because the stars themselves are passing in front or behind each other, causing additional fluctuations in the light seen from Earth.
"The traditional method would have made this hard to do," said Schwamb. "With citizen science, you get a lot of pairs of eyes to stare at this."