(82158) 2001 FP185

(82158) 2001 FP₁₈₅ (provisional designation 2001 FP₁₈₅) is a highly eccentric trans-Neptunian object from the scattered disc in the outermost part of the Solar System, approximately 330 kilometers in diameter. It was discovered on 26 March 2001, by American astronomer Marc Buie at Kitt Peak National Observatory in Arizona, United States.^[2]

(82158) 2001 FP₁₈₅

Discovery[1][2]
Discovered by	M. W. Buie
Discovery site	Kitt Peak National Obs.
Discovery date	26 March 2001
Designations
MPC designation	(82158) 2001 FP185
Alternative designations	2001 FP185
Minor planet category	TNO[1] · SDO[3] · distant[2]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 2
Observation arc	16.25 yr (5,937 days)
Aphelion	420.18 AU
Perihelion	34.280 AU
Semi-major axis	227.23 AU
Eccentricity	0.8491
Orbital period (sidereal)	3425.31 yr (1,251,096 days)
Mean anomaly	1.4289°
Mean motion	0° 0m 1.08s / day
Inclination	30.763°
Longitude of ascending node	179.31°
Argument of perihelion	7.1638°
Physical characteristics
Dimensions	222.59 km (derived)[4] 332±31 km[3][5] 336 km (radiometric)[6]
Geometric albedo	0.046±0.007[5] 0.05 (radiometric)[6] 0.10 (assumed)[4]
Spectral type	IR[3][7] · C[4] B–R = 1.38[3] B–V = 0.860±0.040[8] · 0.820±0.048[9] · 0.820±0.020[7] V–R = 0.520±0.040[8] · 0.572±0.038[9] · 0.580±0.020[7] V–I = 1.070±0.060[8] · 1.013±0.072[9] · 1.060±0.010[7]
Absolute magnitude (H)	5.94±0.03 (R)[8] · 5.940±0.053 (R)[10] · 6.2[1] · 6.38[4][11] · 6.4[6]

Orbit and classification

2001 FP₁₈₅ is a scattered-disc object which belong to the most distant and coldest objects in the Solar System and are thought to be source of most periodic comets.

It orbits the Sun at a distance of 34.3–420.2 AU once every 3425 years and 4 months (1,251,096 days). Its orbit has an eccentricity of 0.85 and an inclination of 31° with respect to the ecliptic.^[1] A first precovery was taken by the Sloan Digital Sky Survey in March 1999, extending the body's observation arc by 2 years prior to its official discovery observation at Kitt Peak.^[2]

Planet Nine co-orbital

If a massive trans-Neptunian object exists, such as the hypothetical Planet Nine, 2001 FP₁₈₅ may be co-orbital with it.^[12][13]

Physical characteristics

Spectra and colors

2001 FP₁₈₅'s color has extensively been measured.^[7][8][9] The object has a determined BR and IR spectra, which are intermediate classes of the very blue BB and very red RR spectra.^[3][7]

Diameter and albedo

According to astronomer Michael Brown and based on radiometric observations, 2001 FP₁₈₅ measures 336 kilometers in diameter and its surface has an (assumed) albedo of 0.05.^[6] Observations with the PACS-instrument of the Herschel Space Observatory during a survey of scattered-disc objects ("TNO are cool") found a similar diameter of 332 kilometer with an albedo of 0.046.^[5] The Collaborative Asteroid Lightcurve Link assumes a higher albedo of 0.10 and consequently derives a much shorter diameter of 222 kilometers based on an absolute magnitude of 6.38.^[4] Brown considers 2001 FP₁₈₅ to be possibly a dwarf planet (see list).^[6]

Lightcurve

No rotational lightcurve of 2001 FP₁₈₅ has been obtained from photometric observations. The body's rotation period, pole axis and brightness amplitude remains unknown.^[4]

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 4 May 2004.^[14] As of 2025, it has not been named.^[2]

See also

• List of Solar System objects by greatest aphelion