Newly Discovered Planet Has Four Parent Stars

Artist interpretation of 30 Ari. Credit: Karen Teramura, UH IfA

Earth only has one parent star, but other planets exist in systems much different than our own. Binary star systems are more common than single stars, and though planets in triple star systems are more rare, they are not unheard of. However, researchers have now identified a planet that is only the second one to ever be discovered in a quadruple star system. The existence of the planet was confirmed through observations from the Palomar Observatory in California. The research has been described in the Astronomical Journal.

The planet, which is considered a "hot Jupiter," has been dubbed 30 Ari and exists in the constellation Aries, 136 light-years from Earth. It is not habitable, as it is incredibly close to its primary star. It only takes three Earth days for the planet to complete one orbit. 

"About four percent of solar-type stars are in quadruple systems, which is up from previous estimates because observational techniques are steadily improving,” co-author Andrei Tokovinin from the Cerro Tololo Inter-American Observatory said in a press release.

Despite the number of quadruple star systems out in the galaxy, 30 Ari is only the second exoplanet in such a system to be confirmed. It follows the 2013 discovery of KIC 4862625, which is about 5,000 light-years away. The planet was discovered via observations from NASA’s Kepler Space Telescope. It is hoped that more planets in unconventional systems will be discovered in order to increase the body of knowledge on how planets form under a variety of conditions.

"Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems," added lead author Lewis Roberts of Jet Propulsion Laboratory. "It's amazing the way nature puts these things together.”

This system is fairly odd, however, because the stars in the system are a long distance away from one another. The primary and secondary star are 44,000 astronomical units (AU) away from one another. One AU is the average distance from the Earth to the sun. The third star in the system is closer to the primary, as it is 28 AU away. The fourth star discovered is the most proximal, at 23 AU. 

Though it seems counterintuitive, the fourth—and closest—star is not believed to have played a role in 30 Ari’s formation. However, the complex gravitational pull from the other three are believed to have influenced the planet’s size.

"This result strengthens the connection between multiple star systems and massive planets," Roberts concluded.

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