Astronomers have discovered a new dwarf planet at the outer limits of the solar system, about two and a half times farther from the Sun than Pluto. This far-flung world is officially named 2015 TG387, but has earned the nickname “Goblin” because it was first observed around Halloween 2015. It is estimated to be some 200 miles (300 kilometers) in diameter, and it takes 40,000 years to complete one trip around the Sun.
The discovery of the dwarf planet was announced Tuesday by the International Astronomical Union's Minor Planet Center, and will be described in a forthcoming paper in The Astronomical Journal, led by Carnegie Institution for Science astronomer Scott Sheppard.
"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," said co-author David Tholen, an astronomer at the University of Hawaii, in a statement. "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 detection of Goblin is the result of a wider effort to root out outer solar system objects, including a mysterious hypothetical Neptune-scale world, nicknamed Planet Nine or Planet X. This speculative planet has not been directly detected, but since 2016, scientists have observed its gravitational pull on objects in the distant solar system. Simulations of Goblin’s orbit, for instance, suggest that the dwarf planet is among the objects that are tugged slightly off-course by Planet X—or some other kind of large mass.
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"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,” co-author Chad Trujillo, an astronomer at Northern Arizona University, said in a statement. “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.”
Sheppard commented that distant worlds like Goblin are “breadcrumbs leading us to Planet X.” As exciting as it is to find this new tiny world, the implication that it might lead to an even bigger planetary catch is just as tantalizing.
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