Was Planet 9 born of a different star?
A team of researchers from Lund University, Sweden, has run a series of computer simulations to test the likelihood that the as-of-yet undiscovered Planet 9 formed in the orbit of an alien star. Whilst the planet has not yet been directly observed, evidence of its gravitational influence may have been observed perturbing the orbits of six Kuiper Belt objects, leading some to assert that Planet 9 boasts a mass around 10 times that of Earth.
There are three leading theories on how such a planet could have come to settle in the highly eccentric and distant orbit it is thought to traverse today. One theory holds that Planet 9 could have been a rogue planet traveling through space alone prior to being captured by our Sun's gravity. Alternatively, the planet could have formed in our solar system, and was subsequently forced out by the influence of neighboring planets, and the gravity of a passing star.
It is also possible that the planet may have been captured from a passing star originating from the same cluster in which our Sun was born. As the alien star traveled close to our own, the Sun's gravitational influence could have ripped the young exoplanet away from its stellar host.
According to the researchers behind the new study, for Planet 9 to be stolen by our Sun it must have traversed a distant orbit from its parent star, and was therefore only tenuously bound. Furthermore, at the point of transfer, the two stars must have passed at a distance of around 150 astronomical units so as not to disturb icy bodies in the Kuiper Belt.
The team input these constraints and ran computer simulations using software designed to calculate the gravitational interactions between planets and stars. In a number of the simulations Planet 9 was wrestled from the alien star, and came to rest in a heliocentric orbit similar to the one that the phantom planet is thought to lay in today.
If Planet 9 is indeed an exoplanet orbiting at the fringes of our solar system, then it could grant astronomers the ability to make unprecedented observations of alien worlds that matured around distant stars.