is the minor planet with the farthest known perihelion in the Solar System, greater than 's. Though its perihelion is farther, has an aphelion only about half of Sedna's. It is the second discovered sednoid, with semi-major axis beyond and perihelion greater than. The similarity of the orbit of to other known extreme trans-Neptunian objects led Scott Sheppard and Chad Trujillo to suggest that an undiscovered object, Planet Nine, in the outer Solar System is shepherding these distant objects into similar type orbits. It has an absolute magnitude of 4.0, which makes it likely to be a dwarf planet, and it is accepted as a dwarf planet by some. It is expected to be about half the size of Sedna and similar in size to Huya. Its surface is thought to have a pink tinge, resulting from chemical changes produced by the effect of radiation on frozen water, methane, and carbon dioxide. This optical color is consistent with formation in the gas-giant region and not the classical Kuiper belt, which is dominated by ultra-red colored objects.
History
Discovery
was first observed on 5 November 2012 with NOAO's 4-meter Víctor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Carnegie's 6.5-meter Magellan telescope at Las Campanas Observatory in Chile was used to determine its orbit and surface properties. Before being announced to the public, it was only tracked by Cerro Tololo Inter-American Observatory and Las Campanas Observatory. It has an observation arc of about 5 years. Two precovery measurements from 22 October 2011 have been reported. A primary issue with observing it and finding precovery observations of it is that at an apparent magnitude of 23, it is too faint for most telescopes to easily observe.
has the largest perihelion distance of any known object in the Solar System. Its last perihelion was around 1979, at a distance of ; it is currently from the Sun., only nine other Solar System objects are known to have perihelia larger than : Sedna, , , , , , , and . The paucity of bodies with perihelia at appears not to be an observational artifact. It is possibly a member of a hypothesized Hills cloud. It has a perihelion, argument of perihelion, and current position in the sky similar to those of Sedna. In fact, all known Solar System bodies with semi-major axes over and perihelia greater than Neptune's have arguments of perihelion clustered near. This could indicate a similar formation mechanism for these bodies. was the first such object discovered. It is currently unknown how acquired a perihelion distance beyond the Kuiper belt. The characteristics of its orbit, like those of Sedna's, have been explained as possibly created by a passing star or a trans-Neptunian planet of several Earth masses hundreds of astronomical units from the Sun. The orbital architecture of the trans-Plutonian region may signal the presence of more than one planet. could even be captured from another planetary system. However, it is considered more likely that the perihelion of was raised by multiple interactions within the crowded confines of the open star cluster in which the Sun formed.
