Astronomers have discovered an exoplanet that orbits its parent stars once every 15,000 years. Its elongated orbit is somewhat reminiscent of the alleged orbit of the hypothetical Planet Nine, a large trans-Neptunian object on the edge of the solar system. As reported in The Astronomical Journal, in the past, the distant gas giant could have been "saved" from escaping from the planetary system by a passing star. The same could have happened with the Ninth planet.
In early 2016, astronomers Michael Brown and Konstantin Batygin presented new evidence for the existence of Planet Nine. Researchers studied the movement of asteroids and minor planets in the Kuiper belt, an area of the solar system beyond the orbit of Neptune, and found anomalies in it that indicated the presence of a large celestial body. According to calculations, the mass of the "invisible" object should be about 10 Earth's, and it should move in a very elongated orbit. It takes 15 thousand years for a body to complete one complete revolution around the Sun, and it does not come closer to it than 300 astronomical units (one astronomical unit is equal to the average distance from the Earth to the Sun).
HD106906 b, a gas giant that may be analogous to Planet Nine, was discovered in 2013 by Magellanic Telescopes at the Las Campanas Observatory in Chile's Atacama Desert. It orbits a binary star in the constellation Southern Cross, located 336 light years from the Sun. The exoplanet's mass is about 11 times the mass of Jupiter, and its age is about 350 times less than the age of the Earth - only 13 million years.
Until now, astronomers did not know anything about the orbital characteristics of the planet. To identify them, Meiji Nguyen of the University of California at Berkeley and colleagues used the Hubble Telescope, which observed HD106906 b for 14 years. It turned out that the celestial body is very far from the parent stars - 730 times farther than the Earth from the Sun. It moves in an inclined and very elongated orbit, making one revolution around two stars in 15 thousand years - like the Ninth Planet around the Sun.
The researchers suggest that HD106906 b formed much closer to its parent stars, at a distance of about three astronomical units. However, due to the action of the force of gravity in the rotating protoplanetary disk, it migrated to its inner edge. Then, the tidal force of the parent stars nearly threw the exoplanet out of the nascent planetary system. A passing star helped to save it from migrating into interstellar space, which stabilized the elongated orbit of HD106906 b (astronomers previously found several candidates in a survey carried out by the Gaia telescope).
Similar events could have happened in the solar system. According to one scenario, Planet Nine formed in the inner part of the solar system, and then was thrown out of it as a result of gravitational interaction with Jupiter. However, Jupiter would most likely push Planet Nine far beyond Pluto. In this case, passing stars could stabilize the orbit of a distant object and prevent it from leaving the solar system.
In the future, astronomers hope to obtain additional data on HD106906 b using the James Webb telescope. This will allow us to understand how the exoplanet was formed, as well as clarify the characteristics of its motion.