(9928) 1981 WE9
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9928 1981 WE9
Discovery [1]
Discovered byPerth Obs.
Discovery sitePerth Obs.
Discovery date16 November 1981
MPC designation(9928)
main-belt[1][2] · Flora[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc65.74 yr (24,012 days)
Aphelion2.6101 AU
Perihelion1.8246 AU
2.2174 AU
3.30 yr (1,206 days)
0° 17m 54.6s / day
Physical characteristics
Dimensions km[4]
3.11 km (calculated)[3]
0.24 (assumed)[3]
14.4[5] · 14.60[4][6] · 14.7[1][3]

, provisional designation , is a stony Florian asteroid from the inner regions of the asteroid belt, approximately 3 kilometers in diameter. It was discovered on 16 November 1981, by astronomers at Perth Observatory in Bickley, Australia.[2]

Orbit and classification

Orbit of (blue), with the inner planets and Jupiter

The stony S-type asteroid is a member of the Flora family, one of the largest groups of asteroids in the main-belt. It orbits the Sun at a distance of 1.8-2.6 AU once every 3 years and 4 months (1,206 days).

Its orbit has an eccentricity of 0.18 and an inclination of 3° with respect to the ecliptic.[1] A first precovery was taken at Palomar in 1951, extending the body's observation arc by 30 years prior to its official discovery observation at Bickley.[2]

Physical characteristics

In December 2014, astronomer Maurice Clark obtained a rotational lightcurve from photometric observations at Preston Gott Observatory. Lightcurve analysis gave an ambiguous rotation period of 18.3980 hours with a brightness variation of 0.41 magnitude, suggesting a non-spheroidal shape (U=2+). The alternative period solution is 9.14 hours with an amplitude of 0.32 magnitude.[8] The results supersede a previously obtained period of 5.547 hours (U=2).[7]

Diameter and albedo

According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the asteroid measures between 2.44 and 3.00 kilometers in diameter, and its surface has an albedo between 0.283 and 0.428.[4][5][6] The Collaborative Asteroid Lightcurve Link assumes an intermediate albedo of 0.24 - derived from 8 Flora, the largest member and namesake of this asteroid family - and calculates a diameter of 3.11 kilometers with an absolute magnitude of 14.7.[3]

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 2 February 1999.[9] As of 2018, it has not been named.[2]


  1. ^ a b c d e "JPL Small-Body Database Browser: 9928 (1981 WE9)" (2017-05-05 last obs.). Jet Propulsion Laboratory. Retrieved 2017.
  2. ^ a b c d "9928 (1981 WE9)". Minor Planet Center. Retrieved 2017.
  3. ^ a b c d e f g "LCDB Data for (9928)". Asteroid Lightcurve Database (LCDB). Retrieved 2017.
  4. ^ a b c d Nugent, C. R.; Mainzer, A.; Masiero, J.; Bauer, J.; Cutri, R. M.; Grav, T.; et al. (December 2015). "NEOWISE Reactivation Mission Year One: Preliminary Asteroid Diameters and Albedos". The Astrophysical Journal. 814 (2): 13. arXiv:1509.02522. Bibcode:2015ApJ...814..117N. doi:10.1088/0004-637X/814/2/117. Retrieved 2017.
  5. ^ a b c d Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results" (PDF). The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved 2017.
  6. ^ a b c d Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 2017.
  7. ^ a b Clark, Maurice (June 2008). "Asteroid Lightcurves from the Chiro Observatory". The Minor Planet Bulletin. 35 (2): 42-43. Bibcode:2008MPBu...35...42C. ISSN 1052-8091. Retrieved 2017.
  8. ^ a b c Clark, Maurice (July 2015). "Asteroid Photometry from the Preston Gott Observatory". The Minor Planet Bulletin. 42 (3): 163-166. Bibcode:2015MPBu...42..163C. ISSN 1052-8091. Retrieved 2017.
  9. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 2018.

External links

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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