Astronomers have spotted the most distant object ever seen in the Solar System: a frigid world that currently lies 103 times as far from the Sun as Earth is. It breaks a record previously held by the dwarf planet Eris, which had been seen at 90 times the Earth-Sun distance.
Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington DC, reported the object on November 10 at the American Astronomical Society’s Division for Planetary Sciences meeting in National Harbor, Maryland.
The object's extreme perch—beyond the edge of the Kuiper belt (home to Eris and Pluto) and into the inner fringes of the next part of the Solar System, known as the Oort cloud—suggests that it could be of scientific significance. Bodies in this primordial realm travel orbits that have remained undisturbed for billions of years.
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But astronomers have not tracked the 103 AU object long enough to know its full path, and there is a chance that it will travel much closer to the Sun than it is currently. 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. “I’d be willing to bet it has some more mundane explanation.”
The long view
Still, the object's discovery gives a rare glimpse at the fringes of the Solar System. Only two worlds are known in the inner Oort cloud: an object called Sedna, discovered by Brown and his colleagues, and another one known as 2012 VP113, popularly nicknamed ‘Biden’ and discovered by Sheppard and Chadwick Trujillo of Gemini Observatory in Hilo, Hawaii.
Sedna never gets closer to the Sun than 76 AU; VP113’s closest approach is 80 AU. If 103 AU is just about as close as the newfound world ever gets to the Sun, it will join the other two objects as a scientifically fascinating resident of the inner Oort cloud.
But if the 103 AU object moves closer to the Sun, past the outer edge of the Kuiper belt at about 50 AU, it will join the ranks of many other, more mundane Kuiper belt denizens whose orbits are particularly stretched-out because of the gravitational influence of the planet Neptune.
Inner Oort cloud objects are more intriguing than Kuiper belt objects because they lie too far away from Neptune to have ever been influenced by its pull, says Sheppard. Instead, their orbits likely reflect primordial conditions in the Solar System, which formed more than 4.5 billion years ago — making them tantalizing targets for astronomers.
Sheppard and Trujillo discovered the 103 AU object using the Subaru telescope atop Mauna Kea, Hawaii. The body is probably well over 500 kilometres—perhaps 800 kilometres—across. The researchers plan to look for the object again next week using the Magellan telescopes in Chile, and then again in a year to calculate its orbit and learn whether it is a true inner Oort cloud object.
This article is reproduced with permission and was first published on November 10, 2015.