The object, a 200-mile-wide rock with the rather inelegant name of 2015 TG387, is some 7.9 billion miles from the sun.
Prof Trujillo, of Northern Arizona University, ran computer simulations for different hypothetical Planet X orbits that explained how 2015 TG387 would actually be shepherded by its gravity.
The theoretical Planet Nine is based on the gravitational pull it exerts on these bodies, with astronomers confident it will be found in the coming years. "The statistics get better and better that this planet is likely out there". Astronomers first observed the dwarf planet in 2015, from the Subaru telescope at Hawaii's Mauna Kea Observatories. The images were taken about 3 hours apart. Only 2012 VP113 and Sedna at 80 and 76 AU respectively have more-distant perihelia than 2015 TG387. Sheppard, along with colleagues at the University of Hawaii, the University of Oklahoma and Northern Arizona University, found the Goblin. But the Goblin, obviously, is under the gravitational influence of a large, undetected object. For context, Pluto's distance is around 34 AU, so 2015 TG387 is about two-and-a-half times further away from the sun than Pluto is right now.
The dwarf planet is estimated to reach some 2,300 Astronomical Units (AU) from the sun at maximum, putting it more than twice as far out as Sedna. So 2015 TG387 is way, way out there.
Given the object's slow movement along an elongated orbit, it took Sheppard and his team a few years of observing to understand the Goblin and its orbit.
"This clustering can only be maintained if the solar system hosts an additional, yet unseen, super-Earth type planet", Batygin said.
The orbits of the newfound extreme dwarf planet 2015 TG387 and its fellow Inner Oort Cloud objects 2012 VP113 and Sedna, as compared with the rest of the solar system.
It's believed to be 300km (186 miles) across, which puts it at the small end of qualifying as a dwarf planet.More news: Everyone in the USA got a text message from President Trump today
That said, little is known about The Goblin. We were lucky we caught The Goblin when we did, says Sheppard, because it's only visible to use with current technology less than one percent of the time.
The few that we do know of behave in a curious way, though.
But going back to the orbit: The Goblin's is similar in key ways to those of some other extremely distant bodies - particularly in an element called "longitude of perihelion".
If Planet X is found, many new questions in the scientific world would arise, such as where did it all come from or if there any possible signs of life.
Confirming the orbit of 2015 TG387 required repeated observations, through May 2018, because the planet moves so slowly. "It turns out that Planet Nine provides a natural avenue for their generation". That has led them to propose the existence of an undiscovered planet several times larger than Earth orbiting far beyond Pluto at hundreds of AU.
At the very edge of our solar system, scientists have discovered a new, extremely distant object billions of miles beyond Pluto.
"We think there are thousands of these, and majority are too distant to detect", Sheppard said.
A look at the relative distance of 2015 TG387.