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Far Out! Icy World Widens Our Solar System's Frontier

An artist's conception shows the icy world Sedna with a moon. Another Sedna-like object has now been detected, suggesting that there could be a substantial population of "inner Oort cloud objects" on the solar system's rim. R. Hurt / NASA / JPL-Caltech

More than a decade after an oddball world named Sedna was discovered on the solar system's far frontier, a fresh discovery reveals that it's not so odd after all. Sedna and the newly found object, called 2012 VP113, may well be the first of a huge new class of celestial bodies.

"This is definitely an evolving field that hopefully will start to get a lot more interesting," said co-discoverer Scott Sheppard, an astronomer at the Carnegie Institution for Science.

Other researchers said the discovery of 2012 VP113 also revives speculation about a bigger world that may be orbiting the sun at a distance of tens of billions of miles, known as Planet X. "This actually is consistent with the existence of such a thing," said UCLA astronomer David Jewett, who did not play a role in the latest discovery.

Sheppard and Chad Trujillo, an astronomer at the Gemini Observatory in Hawaii, describe their find in Thursday's issue of the journal Nature. The discovery is based on a year's worth of observations from telescopes in Chile.

Eccentric and isolated

Like Sedna, 2012 VP113 traces an eccentric orbit that never comes anywhere close to the big planets we all know and love. Neptune, for example, lies 30 astronomical units away from the sun — in other words, 30 times farther away than the Earth-sun distance of 93 million miles (150 million kilometers). 2012 VP113 is more than twice as distant as Neptune. It comes no closer than 80 AU and ranges as far out as 452 AU.

That places the icy world in a region known as the inner Oort cloud, between the Kuiper Belt (a ring of icy worlds including Pluto, at 30 to 50 AU) and the outer Oort cloud (a vast haze of comets surrounding the sun, starting at about 1,500 AU). The zone is considered a "no-man's land" in the solar system.

Image: Outer solar system
This orbital diagram highlights the outer solar system. The sun and terrestrial planets are represented by a speck at the center. The orbits of the four giant planets, Jupiter, Saturn, Uranus and Neptune, are shown by purple solid circles. The Kuiper Belt (including Pluto) is indicated by the dotted light blue region just beyond the giant planets. Sedna's orbit is shown in orange, while 2012 VP113's orbit is shown in red. Scott S. Sheppard / Carnegie Institution for Science

Back in 2004, astronomers were amazed to find Sedna swinging through the inner Oort cloud. At the time, they couldn't definitively explain how it got there.

"People thought, 'If there's one, there's usually more,'" Sheppard told NBC News. "But it took 10 years to find the next one."

Sedna is about 600 miles (1,000 kilometers) wide, with an orbit ranging between 76 and 937 AU from the sun. 2012 VP113 is significantly smaller. Based on its brightness, it's thought to be roughly 200 miles (450 kilometers) wide. Both worlds might qualify as dwarf planets under the International Astronomical Union's definition.

What else is out there?

2012 VP113's significance goes beyond the mere fact of its discovery.

Astronomers have long debated how Sedna, and now this new object, could have gotten into the solar system's no-man's land. Sheppard noted that there are three scenarios in play:

  • A passing star may have disrupted the orbits of the solar system's infant planets, perhaps during a time when the sun was just one of scores or hundreds of stars in a cluster that has since dissipated.
  • Sedna and 2012 VP113 might have been ejected from a different star system and just happened to wander within our sun's gravitational influence.
  • Gravitational interactions during the solar system's formation may have pushed out a rogue planet that disrupted the Kuiper Belt enough to scatter objects like Sedna. This is the Planet X scenario.

Results from NASA's Wide-field Infrared Survey Explorer recently ruled out the existence of a Planet X as big as Jupiter or Saturn. But Trujillo and Sheppard suggest that an as-yet-undetected planet, bigger than Earth but not as big as Neptune, could have done the trick from a distance of hundreds of astronomical units.

Image: Discovery images for 2013 VP113
This composite image shows 2012 VP113, which has the most distant orbit known in our solar system. Three images of the night sky, each taken about two hours apart, have been combined into one. The first image was artificially colored red, the second green and the third blue. 2012 VP113 moved between each image as seen by the red, green and blue dots. The background stars and galaxies did not move, and thus their red, green and blue images combine to show up as white sources. Scott S. Sheppard / Carnegie Institution for Science

The astronomers also report that the orbital angles for far-out solar system objects seem to cluster in a way that suggests most of them were perturbed during a single strong gravitational encounter. "That's really interesting, because it's quite unexpected," Jewitt told NBC News.

Sheppard said it's too early to pick the most promising scenario for the scattering of objects like Sedna and 2012 VP113, but more revelations may be on the way.

"We have several more candidates," Sheppard said from Chile, where he was in the midst of another data-gathering campaign. "It takes about a year of observing to determine whether an orbit is Sedna-like or not."

Sheppard and Trujillo are using the Dark Energy Camera on the NOAO 4-meter telescope in Chile to conduct their survey. Based on the amount of sky covered so far, he and Trujillo estimate that there may be 900 objects in the inner Oort cloud as big as Sedna. They say the total number of objects in what was once thought to be a no-man's land may well exceed the population of the main asteroid belt or the Kuiper Belt.

"It points to the fact that the solar system, even though it's our backyard, is still completely in a phase of discovery," said Jewitt, who was one of the discoverers of the second Kuiper Belt object (after Pluto) in 1992. "We're discovering new realms, and the farther you get from the sun, the less we know — and the more interesting things get."

Update for 2:25 p.m. ET March 26: The discoverers of 2012 VP133 say the object is "affectionately called 'Biden' because of the VP in the provisional name." But Vice President Joe Biden shouldn't get overly excited about that unofficial nickname: The IAU's rules dictate that minor planets can't be named after military or political leaders until they've been dead for 100 years.

The Nature paper by Trujillo and Sheppard is titled "A Sedna-like Body With a Perihelion of 80 Astronomical Units."