Wednesday, November 11, 2015

Astronomers Discover Most Distant Solar System Object Ever

A moving blip in a forest of stars, V774104 was spotted last month by the Subaru telescope in Hawaii. Credit: Subaru Telescope by Scott Sheppard, Chad Trujillo, and David Tholen

Astronomers have found the most distant object ever in our solar system, three times farther away than Pluto. The dwarf planet, which has been designated V774104, is between 500 and 1,000 kilometers across. It will take another year before scientists pin down its orbit, but it could end up joining an emerging class of extreme solar system objects whose strange orbits point to the hypothetical influence of rogue planets or nearby stars.

“We can’t explain these objects’ orbits from what we know about the solar system,” says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., who announced the discovery on Nov. 10 at a meeting of the American Astronomical Society in National Harbor, Maryland. V774104 currently sits 15.4 billion kilometers from the sun, or 103 astronomical units (AU) away.

But astronomers have not tracked the newfound object for long enough to know its full path, and there is a chance that it will travel much closer to the Sun than its current distance of 103 AU. That would make it less interesting to astronomers.

“There’s no reason to be excited yet,” says Michael Brown, a planetary scientist at the California Institute of Technology in Pasadena.

The same deep sky survey, conducted with the Subaru telescope in Hawaii and the Dark Energy Survey Camera in Chile, has also turned up about a dozen other objects around 80 to 90 AU from the sun. Since these distant bodies move around the sky slowly, it will take about a year of follow up observations to understand their orbits – and their origins.

If it turns out their paths will take them inward near Neptune’s orbit, they were probably kicked out of the inner solar system after a brush with Neptune. But Sheppard hopes that some will turn out to belong to a class of true weirdos: the inner Oort Cloud.

Only two other known objects are thought to be members of this exclusive club: Sedna, discovered in 2003, and 2012 VP113, found in 2012. Neither of them ever comes closer to the sun than 50 AU. The rest of the Oort Cloud, which is thought to be a storage lot for long-period comets, extends out a hundred or even a thousand times farther than these objects.

“Sedna and VP113 are the only object in the known solar system whose orbits cannot be explained by things in the known solar system,” says Michael Brown of the California Institute of Technology. They are far enough away from the giant planets to avoid gravitational tweaks to their orbits, and close enough to the sun that they don’t respond to other passing stars.

One explanation for the strange orbits is the pull of a massive but very dark rocky planet. “Something might be shepherding the objects,” Sheppard says.

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