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World at solar system's edge
An artist’s conception shows an object in the distant Kuiper Belt. The newly reported object is beyond the Kuiper Belt, in a region known as the inner Oort Cloud. (Credit: G. Bacon / STScI / NASA)

Astronomers say they’ve identified the most distant celestial object in our solar system – a speck of light more than three times farther out than Pluto, called V774104.

The object is smaller than Pluto or Eris, which rank as the largest known worlds beyond Neptune with diameters of a little less than 1,500 miles (2,400 kilometers). V774104’s brightness suggests that it’s just 300 to 600 miles (500 to 1,000 kilometers) wide. But based on a limited number of observations by the Subaru Telescope in Hawaii, astronomers estimate its distance at more than 9.5 billion miles, or 103 times the distance between the sun and Earth.

The sun-Earth distance, known as an astronomical unit or AU, provides the best measuring stick for distant objects in the solar system. Pluto is currently 33 AU from the sun, and Eris’ distance is 96 AU. V774104 is farther out, in a twilight zone that’s between the belt of icy material called the Kuiper Belt and a halo of comets called the Oort Cloud.

Scott Sheppard, an astronomer at the Carnegie Institution for Science, told what he knew about the object today at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences in National Harbor, Md. But so far, there’s very little that’s known about V774104 – and very much that Sheppard and his colleagues want to find out.

“We don’t know anything about its orbit,” New Scientist quoted Sheppard as saying. “We just know it’s the most distant object known.”

The orbit is key to knowing how to classify V774104: On one hand, it could be an icy world that periodically comes much closer to Neptune’s orbit. If that’s the case, it’s most likely one of the thousands of Kuiper Belt objects that were thrown into crazy orbits through gravitational interactions with the bigger planets. On the other hand, it could be perpetually stuck in the twilight zone – like two other mysterious worlds, Sedna and 2012 VP113 (also co-discovered by Sheppard and known informally as Biden).

If the latter alternative is the case, it adds one more piece to a planetary puzzle: How did those objects get into their current orbits? One suggestion is that there’s an as-yet-undetected “Monster Planet” that’s throwing objects like Sedna out of whack in the inner Oort Cloud. That brings to mind way-out concepts ranging from Planet X to doomsday planet Nibiru.

An alternate suggestion is that Sedna and other objects on the solar system’s fringe were disrupted into weird orbits by a passing star that came close to or even plowed right through the Oort Cloud. To take a walk on the woo-woo side of that idea, do a search for Nemesis or Death Star.

The tamest scenario is that there were merely some unaccounted-for dynamical twists in the development of the solar system that left a few objects orphaned between the Kuiper Belt and the Oort Cloud.

If it turns out that V774104 is one of the orphans, that just might help astronomers figure out which scenario is closest to the mark. Sheppard and his colleagues are continuing their survey of the solar system’s edge, and they expect to have a much better fix on V774104’s orbit a year from now.

Although V774104 now holds the record for most distant known world in the solar system, it’s not the solar system’s most distant identified object: That distinction belongs to NASA’s Voyager 1 probe, which is currently 133 AU from the sun and heading out toward the Oort Cloud. And to put all this in cosmic perspective, the Oort Cloud extends from about 2,000 AU to 50,000 AU or more. The nearest star beyond our sun, Proxima Centauri, is more than 4.2 light-years or 265,000 AU away.

Hat tip to Science’s Eric Hand, Nature’s Alexandra Witze and New Scientist’s Joshua Sokol.

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