Inexplicable path
On Dec. 13, another group said they'd found an object half the mass of Pluto orbiting twice as far from the Sun as Neptune. The object's path has them puzzled.
The faraway world is catalogued as 2004 XR 190 and known temporarily as Buffy. It was discovered as part of the Legacy Survey on the Canada France Hawaii Telescope.
"It was quite bright compared to the usual Kuiper Belt Objects we find," said the University of British Columbia's Lynne Allen, who was part of the international discovery team. "But what was more interesting was how far away it was."
Buffy never gets closer than 52 astronomical units (AU) from the Sun, or 52 times the distance from Earth to the Sun. Neptune is 30 AU from the Sun. Pluto ranges from 30 to 50 AU.
What makes Buffy special is its nearly circular path, which extends out to just 62 AU.
"To find the first known object with a nearly circular orbit beyond 50 AU is indeed intriguing," said Brian Marsden, who runs the Minor Planet Center where all of these objects are catalogued.
Most other known KBOs are on highly elliptical orbits and off-center orbits, typically coming to within 38 AU of the Sun and then soaring out beyond 50 AU. Theory suggests Neptune has acted on them like a gravitational slingshot to produce these eccentric paths.