According to a team of astronomers headed by Dr Lewis Roberts from NASA’s Jet Propulsion Laboratory in Pasadena, an extrasolar gas giant called 30 Arietis Bb (30 Ari Bb) is the second known example of a planet residing in a system with four stars.
The exoplanet 30 Ari Bb orbits its primary star, yellow, in about a year’s time; the star, 30 Ari B, has a companion – the small red dwarf shown at upper left; this pair of stars is itself locked in a long-distance orbit with another pair of stars, upper right, known as 30 Ari A. Image credit: Karen Teramura / UH IfA.
While 30 Ari Bb was known before, it was thought to reside in a system of three stars, not four.
The system, called 30 Ari, is located in the constellation Aries, approximately 136 light-years away.
“Star systems come in myriad forms. There can be single stars, binary stars, triple stars, even quintuple star systems. It’s amazing the way nature puts these things together,” Dr Roberts said.
The planet itself is enormous, with 9.88 times the mass of Jupiter. It orbits its primary star, 30 Ari B, every 335 days. This star has a relatively close partner star, which the planet does not orbit.
The pair, in turn, is locked in a long-distance orbit with another pair of stars about 1,670 AU away.
“It’s highly unlikely that this planet, or any moons that might circle it, could sustain life,” Dr Roberts and his colleagues said.
The first four-star planet, Ph1b, was discovered in the star system Kepler-64 (KIC 4862625) in 2013 by astronomers using data from NASA’s Kepler mission.
The latest discovery, reported in the Astronomical Journal (arXiv.org preprint), suggests that exoplanets in quadruple star systems might be less rare than once thought.
The similarity between Kepler-64 and 30 Ari is that both systems are quadruples consisting of two relatively close pairs that are widely separated.
In fact, recent studies have shown that this type of star systems is itself more common than previously believed.
“About 4% of Sun-like stars are in quadruple systems, which is up from previous estimates because observational techniques are steadily improving,” said team member Dr Andrei Tokovinin of the Cerro Tololo Inter-American Observatory in Chile.
The scientists also reported on a triple-star planetary system, HD 2638, which hosts a so-called hot-Jupiter.
This giant planet, named HD 2638b, orbits its primary star tightly, completing one lap every 3 days.
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Lewis C. Roberts, Jr. et al. 2015. Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars. Astronomical Journal, accepted for publication; arXiv: 1503.01211
