2015 TG387

2015 TG387
Brett Gladman/CFHT/Canadian Astronomy Data Centre (processed by User:Nrco0e) · CC BY-SA 4.0 · source
Name	2015 TG387
Discoverer	David J. Tholen, Scott S. Sheppard, Chad Trujillo
Discovery site	Mauna Kea Observatories
Discovery date	13 October 2015
Mp category	Trans-Neptunian object, Detached object, Sednoid
Epoch	31 May 2020 (JD 2459000.5)
Observation arc	4.99 years
Aphelion	≈ 2100 AU
Perihelion	64.94 AU
Semimajor	≈ 1080 AU
Eccentricity	0.940
Inclination	11.66°
Asc node	300.80°
Arg peri	118.17°
Mean anomaly	0.29°
Mean motion	0° 0m 0.03s / day
Abs magnitude	5.5
Albedo	≈ 0.15 (assumed)
Diameter	≈ 300 km (est.)

2015 TG387 is an extreme trans-Neptunian object and a member of the sednoid population, characterized by its exceptionally distant and elongated orbit around the Sun. Discovered in 2015, its orbit suggests gravitational influences from unseen masses in the outer Solar System, contributing to the ongoing Planet Nine hypothesis. The object's great distance and faintness make it a challenging target for observation, offering valuable clues about the dynamics of the Solar System's frontier.

Discovery and observation

The discovery of 2015 TG387 was announced in 2018 by a team of astronomers including David J. Tholen, Scott S. Sheppard, and Chad Trujillo. Initial observations were made using the Subaru Telescope located at the Mauna Kea Observatories in Hawaii. Follow-up observations to confirm its orbit were conducted with the Magellan Telescopes at the Las Campanas Observatory in Chile. Its detection was part of a broader survey searching for distant Solar System objects, which has also identified other extreme bodies like 2012 VP113 and 90377 Sedna. The object's extremely long orbital period means it has been observed over only a tiny fraction of its path, requiring precise astrometry to calculate its trajectory.

Orbit and classification

2015 TG387 possesses one of the most distant known orbits, with a perihelion of about 65 AU, placing it far beyond Neptune even at its closest approach to the Sun. Its aphelion is estimated to be around 2100 AU, resulting in an orbital period of roughly 40,000 years. This extreme, highly eccentric orbit classifies it as a detached object, meaning it never comes close enough to the giant planets for significant gravitational interaction. It is specifically categorized as a sednoid, a group named for 90377 Sedna, whose members share similar orbital characteristics that cannot be easily explained by perturbations from known planets alone. The clustering of the arguments of perihelion for 2015 TG387 and other sednoids is a key line of evidence cited by proponents of the Planet Nine hypothesis.

Physical characteristics

Due to its immense distance, direct measurement of 2015 TG387's physical properties is extremely difficult. Its apparent magnitude is very faint, and its size is estimated based on an assumed albedo similar to other moderately red trans-Neptunian objects. Current estimates suggest a diameter of approximately 300 kilometers, making it a likely dwarf planet candidate. Its color, inferred from photometry, appears moderately red, which is common among cold classical Kuiper belt objects and other distant bodies, possibly indicating surface compositions rich in organic tholins. Spectroscopic studies from facilities like the Very Large Telescope have been attempted but remain challenging, limiting knowledge of its precise surface composition.

Significance and context

The discovery of 2015 TG387 holds significant importance for understanding the structure and evolution of the outer Solar System. Its orbit, along with those of 90377 Sedna and 2012 VP113, provides dynamical evidence suggesting the possible presence of a massive, undiscovered planet—the hypothetical Planet Nine—in the Solar System's distant reaches. Studying its orbital parameters helps constrain models of the early Solar System, including theories of stellar encounters within the Sun's birth cluster in the Milky Way. As one of the known sednoids, it represents a population of objects whose origins are debated, with proposed formation scenarios involving gravitational scattering by Neptune, capture from other stars, or the influence of a primordial fifth giant planet. Continued observations will refine its orbit and help test these fundamental planetary science hypotheses.

Category:Sednoids Category:Trans-Neptunian objects Category:Astronomical objects discovered in 2015