A massive exoplanet orbiting in a double star system 336 light-years away may be similar to the alleged “Planet Nine” that may exist on the outskirts of our solar system, according to a new study.
The exoplanet, or planet located outside of our solar system, is called HD106906 b and it’s 11 times the mass of Jupiter, the largest known planet in our solar system. It takes 15,000 Earth years for the exoplanet to complete one orbit around the pair of stars.
The study published in The Astronomical Journal Thursday.
Although the exoplanet was discovered in 2013 using the Magellan Telescopes at the Las Campanas Observatory in Chile, researchers were unable to determine its orbit. This led them to question if it was orbiting the two stars or if it was a rogue planet traveling away from the system, unattached to any star.
The Hubble Space Telescope, however, provided accurate measurements of the planet’s movements over a 14-year period.
This is the first time scientists have been able to measure the movement of such a massive planet orbiting so distantly from its star. It’s also the only planet known to be so separated from its stars.
The exoplanet is so far away from its young host stars that the distant is equivalent to 730 times the distance from Earth to the sun. And it explains why this exoplanet’s orbit has been so difficult to track – it’s moving incredibly slowly because of its distance from the host stars, so their gravitational pull on the planet is much weaker.
The young pair of stars, only about 15 million years old compared to our 4.5 billion-year-old sun, are surrounded by a dusty disk of debris. The disk represents the remnants of what it took to create the stars and the same dust from which planets are born. Astronomers have studied this system for the last 15 years because they think planets could be forming in this disk.
Compared to the stars and this disk, the exoplanet is traveling along a rather extremely angled and elongated orbit, tilted about 21 degrees.
“It would be bizarre if, say, Jupiter just happened to be inclined 30 degrees relative to the plane that every other planet orbits in. This raises all sorts of questions about how HD 106906 b ended up so far out on such an inclined orbit,” said lead study author Meiji Nguyen, a junior specialist in astronomy at the University of California, Berkeley, in a statement.
So how did the exoplanet end up in this orbit? It’s likely that it originally formed much closer to the pair of stars, and its orbit brought the planet so close to their stars that their combined gravity essentially knocked the planet away.
This gravitational force could have sent the planet careening out of the star system, but if another star passed by, it would have nudged the exoplanet back into orbit in its home system.
This would have created the unusual orbit the planet has today. The researchers used data from the European Space Agency’s Gaia space observatory to identify several potential stars that may have passed by this system.
The mystery of Planet Nine
If this kind of gravitational dance can impact an exoplanet, it could have occurred during the history of our own solar system, too.
Some scientists believe there is a Planet Nine on the edge of our solar system, farther out than the frozen rocky fragments in the Kuiper Belt beyond Pluto. Given the strange orbits of some of these celestial bodies and dwarf planets beyond Neptune, astronomers think there is a massive, unseen planet that pushed them into a cluster and governs their movements.
Astronomers suggested the planet’s existence in 2012 to explain the phenomenon. But it hasn’t been spotted yet.
However, it’s also possible that these orbits occurred because the objects are exerting their gravitational influence on each other.
“Despite the lack of detection of Planet Nine to date, the orbit of the planet can be inferred based on its effect on the various objects in the outer Solar System,” said study coauthor Robert De Rosa, an astronomer at the European Southern Observatory in Chile, in a statement.
“This suggests that if a planet was indeed responsible for what we observe in the orbits of trans-Neptunian objects it should have an eccentric orbit inclined relative to the plane of the Solar System. This prediction of the orbit of Planet Nine is similar to what we are seeing with HD 106906b.”
Planet Nine, if it exists, likely formed in the inner solar system along with the other planets before Jupiter’s massive gravity kicked Planet Nine out beyond Pluto. And passing stars could have kept Planet Nine in our solar system – just on an orbit that takes it far from our inner solar system.
Astronomers believe the planet is 10 times the size of Earth and moving along an eccentric orbit.
The double star system shows that distant planets can exist and suggests that planets can form early on in the lifetime of a star. It’s not unlikely that our solar system looked like this distant system 4.5 billion years ago.
“We are slowly accumulating the evidence needed to understand the diversity of extrasolar planets and how that relates to the puzzling aspects of our own solar system,” said study coauthor Paul Kalas, an adjunct professor of astronomy at the University of California, Berkeley, in a statement.
In the future, NASA’s James Webb Space Telescope, scheduled for launch in October 2021, could help answer questions about the distant exoplanet orbiting the twin stars.
“There are still a lot of open questions about this system,” De Rosa said. “For example, we do not conclusively know where or how the planet formed. It is likely that both observers and theorists alike will be studying HD 106906 for years to come, unraveling the many mysteries of this remarkable planetary system.”