(528381) 2008 ST₂₉₁, provisional designation 2008 ST₂₉₁, is a 1:6 resonant trans-Neptunian object located in the outermost region of the Solar System that takes almost a thousand years to complete an orbit around the Sun.[5] It was discovered on 24 September 2008 by American astronomers Megan Schwamb, Michael Brown and David Rabinowitz at the Palomar Observatory in California, with no known earlier precovery images.[1]

(528381) 2008 ST₂₉₁

Orbit of (528381) 2008 ST291
Discovery[1][2]
Discovered by	M. E. Schwamb M. E. Brown D. L. Rabinowitz
Discovery site	Palomar Obs.
Discovery date	24 September 2008
Designations
MPC designation	(528381) 2008 ST291
Alternative designations	2008 ST291
Minor planet category	TNO · SDO res 1:6[3]
Orbital characteristics[4]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 3
Observation arc	9.27 yr (3,385 d)
Aphelion	157.437 AU (23.5522 Tm)
Perihelion	42.3114440 AU (6.32970193 Tm)
Semi-major axis	99.8742972 AU (14.94098220 Tm)
Eccentricity	0.5763530
Orbital period (sidereal)	998.30 yr (364,629 d)
Mean anomaly	23.349°
Mean motion	0° 0m 3.6s / day
Inclination	20.758°
Longitude of ascending node	330.97°
Argument of perihelion	324.65°
Physical characteristics
Mean diameter	549 km (est.)[5] 584 km (est.)[3] 612 km[6][7][lower-alpha 1] 345–773 km[7][lower-alpha 2]
Geometric albedo	0.09 (assumed)[3][5]
Apparent magnitude	22.24[6]
Absolute magnitude (H)	4.4[1][4] 4.3[6] 4.6[5]

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 18 May 2019 (M.P.C. 114657).[8] As of 2019, it has not been named.[1]

Orbit and classification

2008 ST₂₉₁ is located at the 1:6 Neptune resonance of 99 AU meaning that it completes roughly 1 orbit for every 6 orbits Neptune makes.[3] It orbits the Sun at a distance of 42.3–157.5 AU once every 998 years and 4 months (semi-major axis of 99.89 AU). Its orbit has an eccentricity of 0.58 and an inclination of 21° with respect to the ecliptic.[4] Currently located at 60.9 AU from the Sun,[6] the object came to perihelion in 1954.[4]

Physical characteristics

Based on an absolute magnitude of 4.4,[1] 2008 ST₂₉₁ is estimated by the Johnston's Archive to be about 584 kilometres (363 mi) in diameter, assuming a typical albedo of 0.09 for trans-Neptunian objects.[3] Astronomer Mike Brown estimates a slightly smaller 549 km from the same albedo and a fainter 4.6 magnitude.[5] The Asteroid Dynamic Site records a brighter 4.3 magnitude, which calculates to 612 km using the same albedo (and same formula as Johnston's); using the average of these magnitudes and a standard assumed minor planet albedo range of 0.25 ~ 0.05, possible sizes of 345 to 773 km are produced.

See also

• List of Solar System objects most distant from the Sun
• List of trans-Neptunian objects

Notes

References

External links

• Orbit Fit and Astrometric record for 528381, Marc W. Buie, SwRI
• List Of Centaurs and Scattered-Disk Objects, Minor Planet Center
• (528381) 2008 ST291 at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• (528381) 2008 ST291 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

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