One Planet Three Stars

One planet, three stars: has the first circumtriple planet ever been found?

Could you imagine watching multiple sunrises and sunsets on a three-star planet? New scientific findings indicate this could be reality for many planets out there in the universe.


Until recently, we had only detected planets orbiting one or, at most, two stars. Even in multiple star systems, the planets’ orbits are limited to one or two stars at once, remaining far away from the others. Astronomers used to debate whether the reason for this is the intrinsic instability of three-or-more star systems or the difficulty in observing the phenomenon. But the mystery seems to be solved now.

“In physics and classical mechanics, the three-body problem is the problem of taking the initial positions and velocities (or momenta) of three-point masses and solving for their subsequent motion according to Newton’s laws of motion and Newton’s law of universal gravitation. The three-body problem is a special case of the n-body problem. Unlike two-body problems, no general closed-form solution exists, as the resulting dynamical system is chaotic for most initial conditions, and numerical methods are generally required. Historically, the first specific three-body problem to receive extended study was the one involving the Moon, Earth, and the Sun. In an extended modern sense, a three-body problem is any problem in classical mechanics or quantum mechanics that models the motion of three particles”. Wikipedia

GW Orionis’ innermost dust ring.

Exoplanets are planets that exist beyond our solar system.  The first exoplanet orbiting three stars, or circumtriple planet, found by scientists resides in the GW Orionis system, a trinary system still in formation that houses planets of its own. Its observation was made possible by a state-of-the-art network of radio telescopes, the best tool for imaging discs of rock, dust, and other material that collide to form what are called protoplanets.

“The Atacama Large Millimeter/submillimeter Array (ALMA) became fully operational in 2013”. Alma Observatory.

GW Orionis is located 1,300 light-years from Earth, in the constellation of Orion. Two of the three stars orbit each other at approximately the Earth-Sun distance of 150 million kilometers, and the third orbits the pair – at nearly the same vast distance that separates Earth and Saturn. Like other young star systems still forming planets, it is surrounded by a big disc of dust and gas, like the one we see around Saturn, but extending up to approximately 400 times the Earth-Sun distance. Unlike Saturn, though, GW Orionis’ disc is split, with a huge gap between the two parts. And this gap intrigued astronomers.

GW Orionis’ rings.

The protoplanetary disc in GW Orionis is the largest and most impressive system of dust rings ever seen. There are three concentric rings of material, none of which align with any of the orbits of the stars. Their outer portion, albeit concentric, does not even align with the other rings, since it is tilted at about 38 degrees as it orbits the stars. The big gap carved in the disc indicates that most of the material there has been cleared out, which usually indicates that planets might be forming there. Scientists have argued whether the gap arose due to a planet’s formation or as the result of the bizarre three-star system dynamics. Upon refined modeling, though, they have concluded that a gas planet as massive as Jupiter is the reason behind the gap in GW Orionis’ disc.


Thus, it seems that GW Orionis houses the first known exoplanet orbiting a trio of stars, in its first million years of existence. This finding was published in September in the Monthly Notices of the Royal Astronomical Society. The study, led by Dr. Jeremy Smallwood, showed that there could be no other way in which the dynamics of the three-star system were responsible for the gap in the disc – in other words, that the gravitational torque of the stars cleared space inside the disc. Instead, the gap is evidence of the first circumtriple planet (or planets) and circumstellar dust rings ever found to orbit around three stars at once.


Unfortunately, if you lived on this strange world, you would not be able to see all three stars at once since the two innermost stars orbit so closely to one another that they would look like a single body in the sky, explains Dr. Rebecca Nealon, from the University of Warwick in England. Yet, she adds, as the planet rotates, the sunrises and sunsets would probably be fascinating and unlike those on any other known world.


Despite the novelty of the discovery, GW Orionis’ observation indicates the phenomenon is not only possible, but it may actually be fairly frequent.  Dr. Alison Young, from the University of Leicester in England, reported that the existence of such a planet could reinforce the notion that planet formation is common in the universe. Furthermore, it could mean that planets are born even in the most unusual systems known to humans. Yet, this research only provides indirect evidence, and directly spotting this new world might be tricky in such a complex system. Scientists still need to find out whether these orbits will remain stable over time. Nonetheless, astronomy research has boomed in the past few decades, and, who knows, maybe we are on the verge of observing a truly unique young world.

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