Even smaller and fainter than Pluto, 2012 VP113 was first spotted a year and a half ago by Scott Sheppard and Chadwick Trujillo, friends who met in grad school at the University of Hawaii and collaborators for 15 years. "There was a chance we'd find a bunch of nothing so it's definitely exciting," Sheppard says of the discovery.
In the time since then, the pair has gathered enough data on the new find, now detailed in a new study in Nature. It's an icy ball of water and methane that measures just 15 degrees above absolute zero. It has a pinkish hue and is 280 miles in diameter—about the size of the state of Wisconsin.
They've even come up with a better name for it than the technical 2012 VP113. Since it has "VP" in the name, they call it "Biden."
Right now, Biden is about 80 times farther away from the sun than the Earth is. From that distance, the sun looks just like a bright star in the sky, Sheppard says. And that's as close as Biden gets. The object has an elongated orbit that can carry it as far away as 450 times the distance between Earth and Sun.
Orbit diagram for the outer solar system. Sedna's orbit is shown in orange while 2012 VP113's orbit is shown in red.
Dwarf planets are the class that now include several objects around the solar system, including Pluto, that are round and big enough to be planets but have not "cleared their neighborhood." Prior to the discovery of Biden, the last such outpost of the solar system was a dwarf planet known as Sedna, which was discovered in 2003. "This is just another Sedna-like object," says Hal Levison, a scientist who studies the formation and evolution of the solar system at the Southwest Research Institute in Colorado.
The discovery means that there could be a swarm of such objects waiting to be discovered out beyond Pluto, Sheppard says, in the area beyond the Kuiper Belt, an icy ring of objects where Pluto is located. "They're in this no-man's-land area. Originally people didn't think there would be anything there," he says. The fact that there are now two large objects found there, Sedna and Biden, has broad implications for how scientists understand both the current and early Solar System.
Peculiarities in the orbits of these two tiny objects hint at more discoveries waiting to be made. Researchers are bound to find more like them, Sheppard says, and some could be very big, "even as big as Mars or Earth." He says there's even the possibility that a super-Earth—10 times the size of our planet—lurks out there. Now, Sheppard and Trujillo are not the first to suggest the existence of an unknown planet in far-flung regions of the solar system. Clyde Tombaugh, for example, discovered Pluto in 1930, looking for a planet thought to be influencing Neptune's orbit and several other distant objects have been proposed to explain everything from comets to mass extinctions. But Levison is guardedly intrigued, even though past searches for a large, faraway planet turned up nothing. "It's seducing me," he says.
These images show the discovery of the new inner Oort cloud object 2012 VP113 taken about 2 hours apart on November 5, 2012. Images by Scott S. Sheppard, Carnegie Institution for Science.
In addition to changing how we think about the current solar system, Sheppard says that the discovery shows what the solar system looked like in the first 100 million years of its existence, when the planets formed around the sun. "It means the solar system was different than it was today, probably more chaotic," he says. Flung way out to edges of the Sun's gravitational field, Biden and Sedna are pieces of forensic evidence that help scientists such as Levison determine this history of the solar system. "It's like a bloody murder scene," Levison says. "Sometimes the blood spattering on the walls tells you more than the bodies on the floor."
If 2012 VP113 is to officially become a dwarf planet, fully sanctioned by the Minor Planet Center, they will have to pick a new name for it ("Biden" will definitely be out of the running). Because it comes from such a cold region, Sheppard is considering looking to Inuit mythology for inspiration, similar to how the names for the major planets come from Roman mythology.
But to get to that point the scientists still need to get in several more years of observations before it fades off into the farthest reaches of the solar system. It won't return for about 4000 years, but perhaps the next time it comes back it'll bring along a bigger sister.