2015 TH₃₆₇

The object's discovery telescope, Subaru (Japanese name for the Pleiades) on the far left, alongside the twin Keck telescopes and NASA's Infrared Telescope Facility

2015 TH₃₆₇ was first observed by Scott Sheppard, Chad Trujillo, and David Tholen on 13 October 2015 using the Subaru Telescope, a large reflecting telescope at the Mauna Kea Observatories on the summit of Mauna Kea with a primary mirror 8.2 meters (27 ft) in diameter.[2] In 2015 it was only observed for 26 days,[2] which is a very short observation arc for a trans-Neptunian object as objects far from the Sun move very slowly across the sky. It is calculated that it will remain in the constellation of Aries from 1994 until 2077. It was announced on 13 March 2018 alongside several other trans-Neptunian objects with a current heliocentric distance greater than 50 AU.[8] The trans-Neptunian objects 2015 TG₃₈₇, 2015 TJ₃₆₇, and V774104 were also discovered by this team on 13 October 2015.

The orbit of 2015 TH₃₆₇ is poorly constrained, as it has only been observed 8 times over less than 1 year due to how dim it is.[3] At a visual apparent magnitude of 26.2,[2] it is about 75 million times fainter than what can be seen with the naked eye,[lower-alpha 2] and it is one of the dimmest asteroids ever observed, only being able to be seen by the largest modern telescopes. It is estimated to have come to perihelion (closest approach to the Sun) around the year 1893±77.[3]

The precise distance of 2015 TH₃₆₇ still remains unknown due to its poorly understood orbit. It is currently outbound roughly 89±4 AU from the Sun,[7] and will require further observations to better refine the orbit. The object has not been observed since October 2016.[1] At magnitude 26, it is only observable with a small number of telescopes that are capable of following it up and refining its orbit. It is expected to come to opposition in the constellation of Aries around 3 November 2018 when it should have a solar elongation of roughly 175°.

There are only 4 known minor planets further from the Sun than 2015 TH₃₆₇ under its nominal orbit as of March 2018, 2014 UZ224 (90.9 AU), Eris (96.1 AU), 2018 VG18 (123.8 AU), and "FarFarOut" (~140 AU).

Observed Solar System objects that periodically become more distant than 89 AU from the Sun include Sedna (which is much larger in size), 2000 CR105, 2012 DR30, 2013 BL76, and 2005 VX3. There are 804 known objects that have aphelia more than 89 AU from the Sun as of March 2018.[9] This distance is about double the outer limit of the torus-shaped Kuiper belt that lies outside Neptune's orbit. Far beyond this region is the vast spherical Oort cloud enshrouding the Solar System, whose presence was deduced from the orbits of long-period comets.

Another distant object publicly known as V774104 was purportedly discovered at around 103 AU on 13 October 2015 by the same team, but public press releases may have confused its distance with 2015 TG387 (V302126).[10][11]

Study of the population of Solar System objects that are significantly more distant than 2015 TH₃₆₇ will likely require new instruments. The proposed Whipple spacecraft mission is designed to determine the outer limit of the Kuiper belt and directly detect Oort cloud objects out to 10,000 AU. Such objects are too small to detect with current telescopes except during stellar occultations. The proposal involves use of a wide field of view and rapid recording cadence to allow detection of many such events.[12]

• List Of Centaurs and Scattered-Disk Objects by the Minor Planet Center
• 2015 TH367 at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 2015 TH367 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters