Spotted: A planet 10 times the size of Jupiter with four suns

Extremely rare discovery: a planet in a quadruple star system

Astronomers have discovered a massive planet with four suns only 125 light-years from Earth.

The planet is at least 10 times as big as Jupiter, and scientists say it probably has no actual surface to stand on. But if you could fly a spacecraft into its atmosphere and look up, you would see one primary sun, a bright red dot, and another star shining more brightly than Venus does in our night sky. 

If you pulled out a telescope, the smallest white star would be revealed to be a binary system of two stars.  

"It would depend on what kind of sky you had, but chances are that at least one of them would be up at any given time," said Lewis Roberts, an astronomer at the Jet Propulsion Laboratory, who helped discover the rare quadruple system.

Astronomers discovered the system known as 30 Ari several years ago, but until recently they thought it was composed of one planet and three stars. They were only able to make out the fourth star in the group after fitting the telescopes at the Palomar Observatory in San Diego with a Robo-AO adaptive optics system.

Adaptive optics allow ground-based telescopes to "see" better by removing the effects of the atmosphere that cause the stars to look like they are twinkling.

"You can almost get to the quality of what you would get from a telescope in space," Roberts said. "So now we can pick out faint stars that couldn't be seen before."

In a paper published in the Astronomical Journal, the researchers describe Ari 30 as a pair of binary systems. A large planet travels around the star known as 30 Ari B, taking about 355 days to complete its orbit.  The newly discovered star is locked in a gravitational dance with 30 Ari B from a distance of less than 30 astronomical units away. (One astronomical unit is the distance between the sun and the Earth).

About 1,670 astronomical units away lie another pair of stars in a system known as 30 Ari A. The two binary systems orbit a common center of mass that lies in between them.

Only one other planet in a quadruple star system has been discovered before, but Roberts said that more may soon be detected.

"There are other known quadruple systems -- there are even known quintuple systems," he said. "As we find more and more exo-planets, we'll probably find some of them in systems like these."

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