4951 Iwamoto

4951 Iwamoto
Discovery [1]
Discovered byY. Mizuno
T. Furuta
Discovery siteKani Obs. (403)
Discovery date21 January 1990
(4951) Iwamoto
Named after
Masayuki Iwamoto
(Japanese astronomer)[2]
1990 BM · 1931 UQ
1985 QN6 · 1985 RH5
1989 WS3
main-belt · (inner)[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc85.45 yr (31,210 days)
Aphelion2.6318 AU
Perihelion1.8824 AU
2.2571 AU
3.39 yr (1,239 days)
0° 17m 26.52s / day
Known satellites1[4][a] (≥ 0.76 Ds/Dp; P: 118 h)
Physical characteristics
Dimensions4.39±0.02 km[4]
5.192±0.043 km[5]
5.515±0.033 km[6]
5.528 km (revised WISE)[7]
5.53 km (taken)[3]
118 h[8]
118.0±0.2 h[b]
0.1844 (revised WISE)[7]
SMASS = S[1] · S[3]
V–R = 0.480±0.030[b]
13.3[1] · 13.74±0.06[3][7][b] · 13.74[6] · 14.01±1.40[9]

4951 Iwamoto, provisional designation 1990 BM, is a stony, synchronous binary[a] asteroid and slow rotator from the inner regions of the asteroid belt, approximately 5.5 kilometers in diameter. It was discovered on 21 January 1990, by Japanese astronomers Yoshikane Mizuno and Toshimasa Furuta at Kani Observatory (403) in Japan.[10]


Animation of 4951 Iwamoto's orbit
   Sun ·    Earth ·   Mars ·    4951 Iwamoto

Iwamoto orbits the Sun in the inner main-belt at a distance of 1.9–2.6 AU once every 3 years and 5 months (1,239 days). Its orbit has an eccentricity of 0.17 and an inclination of 8° with respect to the ecliptic.[1] It was first identified as 1931 UQ at Lowell Observatory in 1931, extending the body's observation arc by 59 years prior to its official discovery observation at Kani.[10]

Physical characteristics[]

In the SMASS classification, Iwamoto is a common S-type asteroid.[1]

Diameter and albedo[]

According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Iwamoto measures 5.192 and 5.515 kilometers in diameter, and its surface has an albedo of 0.218 and 0.186, respectively.[6][5] The Collaborative Asteroid Lightcurve Link adopts Petr Pravec's revised WISE-data, that is, an albedo of 0.1844 and a diameter of 5.528 kilometers with on an absolute magnitude of 13.74.[3][7]

Slow rotator[]

From 25 December 2006 to 23 March 2007, photometric observations of Iwamoto were obtained by the international community of photometrists at Badlands Observatory (SD, USA), Ondřejov Observatory (Czech Republic), Modra Observatory (Slovakia), Carbuncle Hill Observatory (RI, USA), Sonoita Research Observatory (AZ, USA), Kharkiv Observatory (Ukraine), McDonald Observatory (TX, USA), Ironwood Observatory (HI, USA), Leura Observatory (Australia), Skalnaté pleso Observatory (Slovakia), Shed of Science Observatory (MN, USA), Pic du Midi Observatory (France).[a]

Lightcurve analysis gave a rotation period of 118 hours with a brightness variation of 0.34 magnitude (U=3).[b] In May 2011, astronomers Etienne Morelle, Raoul Behrend obtained another lightcurve with a concurring period of 118 hours and an amplitude of 0.38 magnitude.(U=3).[8] With such a long period, Iwamoto is also a slow rotator, as the vast majority of asteroids have a much shorter rotation period of 2.2 to 20 hours.

Binary system[]

During the photometric observations in 2006/7, it was revealed that Iwamoto ("primary") is a synchronous binary system with a minor-planet moon ("secondary") orbiting it every 4.917 days (or 118 hours, which identical to the primary's rotation). Based on the secondary-to-primary mean-diameter ratio (Ds/Dp) of at least 0.76, it was estimated that Iwamoto and its moon measure 4.0 and 3.5 kilometers, respectively.[b] The diameter of Iwamoto has since increased to 5.5 kilometers (see above). The "Jonstonarchive" estimates that the moon has a semi-major axis of 31 kilometers.[4]


This minor planet was named in honor of Japanese astronomer Masayuki Iwamoto (born 1954), a discoverer of minor planets at the Tokushima Observatory (872).[2] The approved naming citation was published by the Minor Planet Center on 5 March 1996 (M.P.C. 26763).[11]


  1. ^ a b c Central Bureau for Astronomical Telegrams
    IAUC 8836 – (4951) Iwamoto
    Photometric observations from 25 December 2006 to 23 March 2007, revealed that (4951) Iwamoto is a synchronous binary asteroid with a rotation period of 118.0±0.2 hours. The combined rotational lightcurve has a brightness variation of 0.34 magnitude. Superimposed mutual occultation/eclipsing events indicate a lower Ds/Dp limit of 0.76. It has an estimated mean abs. magnitude of 13.26±0.05 (Cousins R system), and a measured V–R color index of 0.48±0.03, giving an absolute visual magnitude of 13.74±0.06. This gives a mean-diameter of 4.0 and 3.5 kilometers (± 20%) for the primary and secondary, respectively, assuming a geometric visual albedo of 0.20±0.07 the S-type classified body in the SMASS II taxonomy. The system's parameters are extraordinary in comparison with other known small binaries, in terms of system angular momentum and evolution to its present synchronous state; thus, further observations are warranted.
    Reported by:
  2. ^ a b c d e Pravec (2007) web: rotation period 118.0±0.2 hours with a brightness amplitude of 0.34 mag. Quality code = 3. Summary figures at Collaborative Asteroid Lightcurve Link (CALL) and Pravec, P.; Wolf, M.; Sarounova, L. (2007)


  1. ^ a b c d e f "JPL Small-Body Database Browser: 4951 Iwamoto (1990 BM)" (2017-03-29 last obs.). Jet Propulsion Laboratory. Retrieved 4 July 2017.
  2. ^ a b Schmadel, Lutz D. (2007). "(4951) Iwamoto". Dictionary of Minor Planet Names – (4951) Iwamoto. Springer Berlin Heidelberg. p. 426. doi:10.1007/978-3-540-29925-7_4831. ISBN 978-3-540-00238-3.
  3. ^ a b c d e "LCDB Data for (4951) Iwamoto". Asteroid Lightcurve Database (LCDB). Retrieved 29 March 2017.
  4. ^ a b c Johnston, Robert (21 September 2014). "(4951) Iwamoto". johnstonsarchive.net. Retrieved 29 March 2017.
  5. ^ a b c Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121. Retrieved 29 March 2017.
  6. ^ 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". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
  7. ^ a b c d Pravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026. Retrieved 29 March 2017.
  8. ^ a b Behrend, Raoul. "Asteroids and comets rotation curves – (4951) Iwamoto". Geneva Observatory. Retrieved 29 March 2017.
  9. ^ 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 29 March 2017.
  10. ^ a b "4951 Iwamoto (1990 BM)". Minor Planet Center. Retrieved 29 March 2017.
  11. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 29 March 2017.

External links[]