A team of astronomers claims to have compelling new evidence that a planet, larger than the Earth, lies undiscovered in our Solar System.
They say the existence of the new world – dubbed Planet X or Planet Nine – is given away by the effect it has on a smaller object dubbed the Goblin that they have found far beyond Neptune and Pluto.
The new icy body, whose discovery was only revealed today, got its nickname because its catalogue label is 2015 TG387 and it was first spotted around Halloween.
Since that find, three years ago, astronomers have been secretly monitoring the movement of the Goblin to determine the shape of its 40,000-year long orbit around the Sun.
It appears to be part of a swarm of asteroid-like objects, on the fringes of the Solar System, called the Oort Cloud. The Goblin is currently more than twice as far away as Pluto, at a distance 80 times that of the Earth from the Sun. (The mean distance of the Earth from the Sun is known as an Astronomical Unit, or AU).
But it travels on a very elongated orbit. It never gets closer than 65 AU, when it is at perihelion, and recedes to an incredible distance of 2,300 AU.
The Goblin is far enough away that its orbit does not get disturbed significantly by the gravitational pull of the giant planets, such as Jupiter and Neptune. Only two other bodies in the Solar System, called Sedna and 2012 VP113, are known to have orbits that never bring them closer to the Sun.
Pluto is a dwarf planet that stands like a gatekeeper to a zone packed with countless icy objects, called the Kuiper Belt. Bodies like Sedna, and now the Goblin, which like beyond this collection of debris, are known as Scattered Disk Objects by astronomers.
Further out still lies a vast reservoir of billions of icy bodies, called the Oort Cloud. It forms a ghostly shell around the whole of the Solar System. The cloud has never been directly observed, but is named after Jan Oort, a Dutch astronomer who suggested its existence in 1950. The cloud is thought to begin about a light-year from the Sun and may stretch a third of the way to the nearest star. It is a region filled with frozen fragments of water, ammonia and methane left over from the formation of the Solar System.
One of the Goblin’s co-discoverers, Scott Sheppard of the Carnegie Institution for Science, in Washington, DC, said: “These so-called Inner Oort Cloud objects like 2015 TG387, 2012 VP113, and Sedna are isolated from most of the Solar System’s known mass, which makes them immensely interesting.
“They can be used as probes to understand what is happening at the edge of our Solar System.”
Sheppard and colleague Chad Trujillo, of Northern Arizona University, also discovered VP113 in 2012. They subsequently noticed that its orbit, and that of several other extremely remote minor bodies in the Solar System, followed similar orbits. This led them to suggest that their orbits were being controlled by a new giant planet in the depths of the Solar System.
David Tholen, of the University of Hawaii, was also part of The Goblin’s discovery team, which is surveying the sky for new icy objects in the outer Solar System.
He said: “We think there could be thousands of small bodies like 2015 TG387 out on the Solar System’s fringes, but their distance makes finding them very difficult.
“Currently we would only detect 2015 TG387 when it is near its closest approach to the Sun. For some 99 per cent of its 40,000-year orbit, it would be too faint to see.”
Sheppard added: “These distant objects are like breadcrumbs leading us to Planet X. The more of them we can find, the better we can understand the outer Solar System and the possible planet that we think is shaping their orbits. ” He said such a discovery “would redefine our knowledge of the Solar System’s evolution.”
The Goblin is probably itself only about 300 km (200 miles) wide. Its discovery has not been announced earlier because the discovery team needed time to confirm its orbit. They first spotted it on images taken in October 2015 with the Japanese Subaru 8-meter telescope located on Mauna Kea in Hawaii.
Confirmation images which helped map its orbit were made using the Magellan telescope at Carnegie’s Las Campanas Observatory in Chile and the Discovery Channel Telescope in Arizona in 2015, 2016, 2017 and 2018.
Mapping of its orbit revealed that 2015 TG387 reaches perihelion in a similar region of the sky to 2012 VP113, Sedna, and most other known extremely remote trans-Neptunian objects. The team say that this suggests Planet X is shepherding them into similar types of orbits.
Trujillo ran computer simulations with Nathan Kaib, of the University of Oklahoma. These showed that the smaller bodies’ orbits could be influenced by a super-Earth-mass planet on an elongated orbit, several hundred AU from the Sun. The existence of such a world was proposed by Caltech’s Konstantin Batygin and Michael Brown in 2016.
Trujillo commented: “What makes this result really interesting is that Planet X seems to affect 2015 TG387 the same way as all the other extremely distant Solar System objects. These simulations do not prove that there’s another massive planet in our solar system, but they are further evidence that something big could be out there.”
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