5642 Bobbywilliams, provisional designation 1990 OK1, is an eccentric, stony asteroid and Mars-crosser from the inner regions of the asteroid belt, approximately 4.7 kilometers in diameter.

5642 Bobbywilliams
Discovery [1]
Discovered byH. E. Holt
Discovery sitePalomar Obs.
Discovery date27 July 1990
MPC designation(5642) Bobbywilliams
Named after
Bobby G. Williams
(JPL engineer)[2]
1990 OK1
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc41.97 yr (15,330 days)
Aphelion3.0867 AU
Perihelion1.5454 AU
2.3161 AU
3.52 yr (1,287 days)
0° 16m 46.56s / day
Physical characteristics
Dimensions4.71 km (calculated)[4]
4.8341±0.0003 h[5]
0.20 (assumed)[4]
14.0[1][4] · 14.24±0.23[6]

It was discovered on 27 July 1990, by American astronomer Henry E. Holt at Palomar Observatory in California, United States.[3] The asteroid was named for JPL engineer Bobby Williams.[2]


Orbit and classificationEdit

Bobbywilliams orbits the Sun in the inner main-belt at a distance of 1.5–3.1 AU once every 3 years and 6 months (1,287 days). Its orbit has an eccentricity of 0.33 and an inclination of 25° with respect to the ecliptic.[1] A first precovery was taken at the Australian Siding Spring Observatory in 1975, extending the body's observation arc by 15 years prior to its official discovery at Palomar.[3]

Physical characteristicsEdit

Rotation periodEdit

In July 2011, a rotational lightcurve of Bobbywilliams was obtained from photometric observations by astronomer Julian Oey at both the Australian Kingsgrove (E19) and Leura (E17) observatories. Lightcurve analysis gave a well-defined rotation period of 4.8341 hours with a brightness variation of 0.05 magnitude (U=3).[5]

Diameter and albedoEdit

The Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 4.71 kilometers with an absolute magnitude of 14.0.[4]


This minor planet was named for Jet Propulsion Laboratory engineer Bobby G. Williams (born 1951), specialized in celestial mechanics and the navigation of space probes. He has been a leading navigation manager when NEAR Shoemaker had its rendezvous with the asteroids 253 Mathilde and 433 Eros,[2] The official naming citation was published by the Minor Planet Center on 28 July 1999 (M.P.C. 35483).[7]


  1. ^ a b c d e "JPL Small-Body Database Browser: 5642 Bobbywilliams (1990 OK1)" (2017-03-29 last obs.). Jet Propulsion Laboratory. Retrieved 21 June 2017.
  2. ^ a b c Schmadel, Lutz D. (2007). "(5642) Bobbywilliams". Dictionary of Minor Planet Names – (5642) Bobbywilliams. Springer Berlin Heidelberg. pp. 478–479. doi:10.1007/978-3-540-29925-7_5346. ISBN 978-3-540-00238-3.
  3. ^ a b c "5642 Bobbywilliams (1990 OK1)". Minor Planet Center. Retrieved 1 August 2016.
  4. ^ a b c d e f "LCDB Data for (5642) Bobbywilliams". Asteroid Lightcurve Database (LCDB). Retrieved 1 August 2016.
  5. ^ a b Oey, Julian (July 2012). "Lightcurve Analysis of Asteroids Observed in 2011 from Leura and Kingsgrove Observatories". The Minor Planet Bulletin. 39 (3): 145–147. Bibcode:2012MPBu...39..145O. ISSN 1052-8091. Retrieved 1 August 2016.
  6. ^ Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 1 August 2016.
  7. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 1 August 2016.

External linksEdit