Astronomers confirm that the planet’s bound orbit is far from its star, demonstrating that distant planets exist.
In the far reaches of our solar system, scientists are still searching for a hypothetical ‘Planet Nine,’ but an exoplanet 336 light-years from Earth is gradually looking like the star system’s Planet Nine.
Earth Nine, which, in an extremely eccentric orbit around the Sun, could be ten times the size of Earth and orbits well beyond Neptune, was suggested in 2012 to describe anomalies in the orbits of dwarf planets just beyond the orbit of Neptune, so-called detached objects of the Kuiper Belt.
If it exists, it has not yet been found.
In 2013, far from the star HD 106906, the only known planet at such a great distance, a similarly unusual extrasolar planet was discovered.
While much heavier than the projected mass of Planet Nine – maybe 11 times the mass of Jupiter or 3,500 times the mass of Earth – it too sat in a very unexpected position, well above the dust plane of the solar system and tilted at an angle of about 21 degrees.
So far, the major question has been whether the planet, named HD 106906 b, is in an orbit forever bound to a binary star, which is just 15 million years old, compared to our sun’s 4.5 billion-year-old period, or is on its way out of the solar system, never to return.
Astronomers are finally offering an answer to that question in a paper published in The Astronomical Journal in December 2020.
By closely observing the location of the planet over 14 years, they determined that in a 15,000-year, highly eccentric orbit, it is possibly locked to the star, making it a distant cousin of Planet Nine.
If it is in a highly eccentric orbit around the binary star, “that raises the question of how these planets got to such large distances,” said Meiji Nguyen, a graduate student at UC Berkeley and the paper’s lead author. “Were they scattered from the inner solar system? Or did they form out there?”
According to the first scientist, Paul Kalas, an associate professor of astronomy at the University of California, Berkeley, the resemblance to the orbit of the proposed Planet Nine indicates that such distant planets can actually exist and that they can form within the first tens of millions of years of the existence of a star.
And the planet appears to support a scenario in which passing stars also play a part, based on the team’s other recent observations about HD 106906.
“Something happens very early that starts nudging planets and comets outward, and then you have passing stars stabilizing their orbits,” he said. “We’re slowly accumulating the evidence we need to understand the diversity of extrasolar planets and how that relates to the puzzling aspects of our own solar system.”
A dusty, young star with a mysterious planet
HD 106906 is a cluster of binary stars located in the Crux constellation.
Over the past 15 years, astronomers have thoroughly studied it because it has a prominent dust disk that may give birth to planets. Our solar system may have looked like HD 106906 around 4.5 billion years ago, when planets formed from the formation of the Sun in the swirling disk of debris left over.
Surprisingly, the star photos taken by Magellan’s telescopes in Chile in 2013 showed a planet glowing at an extremely large distance from the binary star from its own internal heat: 737 times farther away from the binary star than Earth is from the Sun (737 astronomical units, AU).
That is 25 times farther away from the star than the Sun is from Neptune.
Kalas, who searches for planets and dust disks around young stars, led a team that used the Gemini Planet Imager on the Gemini South Telescope to obtain the first images of the star’s debris disk.
These observations provided evidence in 2015 that led theorists to conclude that the planet formed near the binary star and was ejected because of gravitational interactions with the binary.
Proof: the outer dust disk of the star and the inner comet belt are askew, indicating that the alignment was broken by something – the world.
The theory is that the material is thrown into the disk once the planet approaches the binary star,”The idea is that every time the planet approaches the binary star, it throws up the material in the disk,”