CAPE CANAVERAL, FLORIDA – Astronomers have found a dwarf planet far beyond the orbit of Pluto and can only guess how it got there.
The diminutive world, provisionally called 2012 VP113 by the international Minor Planet Center, is estimated to be about 450 kilometers (280 miles) in diameter — one-eighth the width of the moon and less than half the size of a neighboring dwarf planet named Sedna, which was discovered a decade ago. By comparison, Earth is about 12,700 kilometers (7,900 miles) across.
Unlike red and shiny Sedna, the newfound object is pinker and much fainter, which made it hard to detect. Its pink tinge comes from ice, methane and carbon dioxide that have been damaged by radiation.
Sedna and VP are the first objects found in a region of the solar system that previously was believed to be devoid of planetary bodies. The no man’s land extends from the outer edge of the Kuiper Belt, home to the dwarf planet Pluto and more than 1,000 other small icy bodies, to the Oort cloud, which orbits the sun some 10,000 times farther away than Earth’s average of 150 million kilometers (93 million miles).
The inner Oort cloud is where some comets such as the sun-diving Comet ISON are thought to originate. ISON broke apart late last year after brushing too close to the sun.
“When Sedna was discovered 10 years ago, it kind of redefined what we thought about the solar system,” astronomer Scott Sheppard of the Carnegie Institution of Washington said in an interview.
Nothing in the appearance of the modern-day solar system can account for Sedna and VP’s existence, say astronomers who published their findings on Wednesday in the journal Nature.
Sedna’s 11,400-year orbit takes it only as close as 76 times the distance of Earth’s orbit. VP’s closest approach is 80 times farther than Earth’s orbit — roughly twice as far as the Kuiper Belt.
“In the current architecture of the solar system, Sedna and 2012 VP113 should not be there,” wrote astronomer Megan Schwamb, of the Academia Sinica in Taipei, in a separate Nature article.
“Effectively frozen in place and untouched as the solar system evolved to its present state,” the dwarf planets “preserve the dynamical signature of whatever event scattered these bodies to such distances,” Schwamb wrote. In doing so, she said, they act as “fingerprints at a crime scene,” allowing scientists to test their theories on the formation of the sun and planets.
Computer simulations provide a few potential scenarios.
Lead researcher Chad Trujillo favors the idea that a sibling star forming in the same stellar nursery as the sun gravitationally elbowed some Oort Cloud residents inward as it flew by.
Sheppard suggests that another planet at least as massive as Earth got bumped out of the solar system, taking some Kuiper Belt bodies with it along the way. That renegade planet or planets actually may still be lurking in the farthest reaches of the solar system, too dim and remote to be detected by currently available telescopes and cameras, Sheppard said.
A third option is that the sun has a companion with large planets in distant orbits whose gravity is pinning Sedna, VP and potentially millions of other dwarf-like planets in unusual and distant orbits.
“With our discovery of one more object, we can’t rule out one theory or another,” Trujillo said.
More residents of the region, now known as the inner Oort Cloud, soon may make their presence known.
Astronomers are working to confirm six other Sedna-like objects found last year. That requires imaging the mini-planets several times over a year or longer to measure how much they have moved relative to background stars.
“They’re really hard to find,” Trujillo said.
The objects are hard to spot because they are so far away and it takes a long time for them to swing nearer the sun. Sedna and VP were spotted at their closest approach to the sun.
Astronomers suspect there may be 150 million Sedna-like dwarf planets measuring between 50 and 8,000 kilometers (31 and 5,000 miles) in diameter, a larger population than the Kuiper Belt objects.
“Finding Sedna so far away seemed odd and potentially a fluke. But this one is beginning to make it look like that might be a typical place for objects to be. Not at all what I would have guessed,” Mike Brown, an astronomer at the California Institute of Technology, said in an email. Brown led the Sedna team but was not part of the new discovery.
VP is currently the third-farthest object in the solar system, after dwarf planet Eris and Sedna, but it has an eccentric, elongated orbit that can take it out to 68 million kilometers (42 billion miles) from the sun. Sedna can loop out as far as 135 million kilometers (84 billion miles) from the sun at its farthest point.
VP is jokingly nicknamed “Biden” after U.S. Vice President Joe Biden because of its initials. The rules of the International Astronomical Union prevent researchers from naming objects in space after politicians, so they are considering a name from Eskimo mythology because the planet is extremely cold, Sheppard said.