Our solar system is home to far more worlds than you might think. While there are only eight known planets, there could be thousands of dwarf planets – Pluto-sized or smaller – lurking at the very edges of the Sun's influence. Now, astronomers have spotted a new distant dwarf with an incredibly wide orbit, lending further evidence to the idea that a much bigger "Planet X" is out there somewhere.
Although the object is officially known as 2015 TG387, it was apparently given the much-catchier nickname "The Goblin" because it was first spotted near Halloween. It's pretty puny, even by dwarf planet standards – with a diameter of less than 300 km (186 mi) it's only roughly a tenth the size of our Moon.
But the really amazing thing about the Goblin dwarf is its extremely long orbit. TG387 only completes one trip around the Sun every 40,000 years, and at the furthest point of its journey it swings out to a distance of 2,300 Astronomical Units (AU). For reference, the Earth is 1 AU from the Sun, and even Pluto only ever gets as far away as 49 AU.
That said, the Goblin is relatively close right now, at a distance of "only" 80 AU. At its absolute closest point the dwarf planet gets to within 65 AU of the Sun. Given how tiny the object is, there's a good chance we'd never have seen it at all if it was at a different point in its journey.
"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," says David Tholen, co-author of a study describing the object. "Currently we would only detect 2015 TG387 when it is near its closest approach to the Sun. For some 99 percent of its 40,000-year orbit, it would be too faint to see."
The Goblin was first observed in October 2015, with follow-up observations to plot out its orbit taking place over the three years since. It was discovered as part of an ongoing search for objects on the fringes of the solar system, with a particular focus on Planet X. This hypothetical world is believed to have the mass of several Earths and orbit a few hundred AU from the Sun, but it's never been directly detected.
That said, the evidence is continuing to mount that this heavyweight is hiding out there. Mathematical models have found that the unusual orbits of objects beyond Neptune could be explained by the gravitational tug of a Super-Earth from the shadows, and its influence might even be visible in the tilt of the Sun.
The team behind the new discovery say that simulating the Goblin's odd orbit adds further evidence of Planet X. The perihelion of this new dwarf seems to line up suspiciously well with that of other known distant objects, which could suggest that something is pushing them into similar paths.
"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," says Chad Trujillo, co-author of the study. "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."
Of course, it's all still conjecture until we actually find the damn thing. Other scientists suggest the weird orbits of Kuiper Belt objects might just be them jostling each other like bumper cars, while yet others say there might be even a Mars-sized 10th planet out there too. The search will no doubt continue.
The research was submitted for publication in The Astronomical Journal.
Source: Carnegie Institution for Science
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