Astronomy:2015 TG387

2015 TG₃₈₇

2015 TG387 has an elongated orbit (at lower right); it has the greatest aphelion of the three known sednoids
Discovery
Discovered by	David J. Tholen Scott S. Sheppard Chad Trujillo
Discovery date	October 13, 2015
Designations
MPC designation	2015 TG387
Alternative designations	V302126
Minor planet category	TNO · E-SDO · sednoid
Orbital characteristics
Epoch 2018-Mar-23 (JD 2458200.5)
Uncertainty parameter 4
Observation arc	949 days (2.60 yr)
|{{{apsis}}}|helion}}	2037 AU
|{{{apsis}}}|helion}}	64.8 AU
Semi-major axis	1051 AU
Eccentricity	0.94
Orbital period	34080 years
Mean anomaly	359.4°
Mean motion	0.00002892°/day
Inclination	11.66°
Longitude of ascending node	300.90°
|{{{apsis}}}|helion}}	118.3°
Physical characteristics
Dimensions	~300 km (190 mi)
Absolute magnitude (H)	5.3

2015 TG₃₈₇ (also known under its provisional designation V302126, nicknamed The Goblin for the letters TG and because its discovery was near Halloween), is a trans-Neptunian object and sednoid in the outermost part of the Solar System. It was first observed on October 13, 2015, by astronomers David J. Tholen, Scott S. Sheppard, and Chad Trujillo with the Subaru Telescope at Mauna Kea Observatories, and publicly announced on October 1, 2018.

Physical characteristics

2015 TG₃₈₇ is estimated to be 300 km (190 mi) in diameter. A precise size estimate is difficult to determine due to its faintness, comparable to one of Pluto's smaller moons (24th magnitude in the late 2010s when it was identified). The current size estimate is based on assumptions about 2015 TG₃₈₇'s albedo: if it is a darker object then it would also have to be larger; a higher reflectivity would demand that it be smaller.

By observing 2015 TG₃₈₇'s color and apparent brightness, in combination with various methods and other known data about Trans-Neptunian objects, it is possible to develop a model based on the predicted size, reflectivity, and spectrum:

Examples of various Trans-Neptunian objects for comparison

Sedna, another body hundreds of AU from the sun, is relatively dark and red compared to icy bodies, which tend to be brighter and whiter. One way to understand TG387 is to compare observations in the infrared and visible light with a telescope using a spectrometer.

Orbit

2015 TG₃₈₇ is the third sednoid to be discovered, following 90377 Sedna and 2012 VP113.

Implications of orbit

Along with the similar orbits of other distant trans-Neptunian objects, the orbit of 2015 TG₃₈₇ suggests, but does not prove, the existence of a hypothetical Planet Nine in the outer Solar System.

(As of 2018), the object is 80 AU from the Sun; about two-and-a-half times farther out than Pluto's current location. As with Sedna, it would not have been found had it not been on the inner leg of its long orbit. This suggests that there may be many similar objects, most too distant to be detected by contemporary technological methods. Following the discovery of 2015 TG₃₈₇, Sheppard et al. concluded that it implies a population of about 2 million inner Oort cloud objects larger than 40 km (25 mi), with a combined total mass of 1×10²² kg, which is several times the mass of the asteroid belt.

Visualizations

• 

  Simulated view of solar system as seen from 2015 TG₃₈₇, showing the orbits of major planets and positions of other extreme trans-Neptunian objects.

• 

  View of 2015 TG₃₈₇ from earth, showing retrograde loops every year, with current position near γ Pegasi

See also

• List of Solar System objects most distant from the Sun in 2018
• List of Solar System objects by greatest aphelion

See also

• List of Solar System objects by greatest aphelion

External links

• 2015 TG387 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters