(48639) 1995 TL8

(48639) 1995 TL₈ is a binary trans-Neptunian object from the scattered disc in the outermost regions of the Solar System. It was discovered by Arianna Gleason in 1995 and measures approximately 176 kilometers in diameter. Its 80-kilometer minor-planet moon was discovered on 9 November 2002.^[5]

(48639) 1995 TL₈

1995 TL8 and its satellite (unresolved) imaged by the Hubble Space Telescope
Discovery[1][2]
Discovered by	A. Gleason (Spacewatch)
Discovery site	Kitt Peak National Obs.
Discovery date	15 October 1995
Designations
MPC designation	(48639) 1995 TL8
Alternative designations	1995 TL8
Minor planet category	TNO[1] · Other TNO[3] detached[4] · distant[2]
Orbital characteristics[1]
Epoch 17 December 2020 (JD 2459200.5)
Uncertainty parameter 2
Observation arc	25.26 yr (9,225 days)
Aphelion	65.218 AU
Perihelion	39.937 AU
Semi-major axis	52.578 AU
Eccentricity	0.2404
Orbital period (sidereal)	381.25 yr (139,251 days)
Mean anomaly	46.972°
Mean motion	0° 0m 9.36s / day
Inclination	0.2499°
Longitude of ascending node	260.007°
Argument of perihelion	84.397°
Known satellites	1 (D: 80 km)[5]
Physical characteristics
Dimensions	176 km[5] 420.27 km (calculated)[6] 495 km (estimated)[7]
Geometric albedo	0.07 (estimated)[7] 0.10 (assumed)[6] 0.369[5]
Spectral type	RR[8] · C (assumed)[6]
Absolute magnitude (H)	4.667±0.091 (R)[9] · 4.8[1][6] · 5.1[7] · 5.290±0.060[a]

Discovery

1995 TL₈ was discovered on 15 October 1995, by American astronomer Arianna Gleason as part of UA's Spacewatch survey at Kitt Peak National Observatory, near Tucson, Arizona.^[2]

It was the first of the bodies presently classified as a scattered-disc object (SDO)^{[3][failed verification]} to be discovered, preceding the SDO prototype (15874) 1996 TL66 by almost a year.^[10]

Satellite

Animation of two Hubble images of 1995 TL₈'s satellite in August 2001

Comparison of mean separation distances and diameters of trans-Neptunian close binaries, including 1995 TL₈

A companion was discovered by Denise C. Stephens and Keith S. Noll, from observations with the Hubble Space Telescope taken on 9 November 2002, and announced on 5 October 2005. The satellite is relatively large, having a likely mass of about 10% of the primary. Its orbit has not been determined, but it was at a separation of only about 420 kilometres (260 mi) to the primary at the time of discovery, with a possible orbital period of about half a day and an estimated diameter of 161 kilometres (100 mi).^[5]

A relative size and distance comparison of the 1995 TL₈ system with the Earth–Moon system. The scale of the Earth–Moon system has been reduced so Earth appears the same size as the 1995 TL₈ primary.

Scattered–extended object

1995 TL₈ is classified as detached object (scattered–extended) by the Deep Ecliptic Survey, since its orbit appears to be beyond significant gravitational interactions with Neptune's current orbit.^[4] However, if Neptune migrated outward, there would have been a period when Neptune had a higher eccentricity.

Simulations made in 2007 show that 1995 TL₈ appears to have less than a 1% chance of being in a 3:7 resonance with Neptune, but it does execute circulations near this resonance.^[11]

Left: The near 3:7 resonance pattern of 1995 TL₈ with Neptune only moves clockwise. It never halts and reverses course (i.e. librates).
Right: The orbital period of 1995 TL₈ missing the 7:3 (2.333) resonance of Neptune

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 20 November 2002.^[12] As of 2025, it has not been named.^[2]

See also

• 3753 Cruithne (orbital circulations due to near resonant perturbations with Earth)
• (131696) 2001 XT254 – to see a proper 3:7 resonance with Neptune

Notes

1. Lellouch (2013): observations on 11 February 2011 gave an absolute magnitude of 5.290±0.060. Summary figures for (48639) at LCDB not found at ADS (2013A&A...557...60L)