5331 Erimomisaki, provisional designation 1990 BT1, is a background asteroid on an eccentric orbit from the central regions of the asteroid belt, approximately 10 kilometers (6 miles) in diameter. It was discovered on 27 January 1990, by Japanese amateur astronomers Kin Endate and Kazuro Watanabe at the Kitami Observatory on Hokkaidō, Japan.[1] The asteroid has a longer-than-average rotation period of 24.26 hours.[8] It was named after Cape Erimo at the southern tip of Hokkaidō.[1]

5331 Erimomisaki
Discovery [1]
Discovered byKin Endate
K. Watanabe
Discovery siteKitami Obs.
Discovery date27 January 1990
MPC designation(5331) Erimomisaki
Named after
Cape Erimo[1]
(Hokkaidō, Japan)
1990 BT1 · 1984 YY2
main-belt[1][2] · (middle)
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc33.33 yr (12,174 d)
Aphelion3.8450 AU
Perihelion1.6826 AU
2.7638 AU
4.59 yr (1,678 d)
0° 12m 52.2s / day
Physical characteristics
Mean diameter
9.208±0.323 km[4][5]
9.549±2.062 km[6]
10.57±0.15 km[7]
16.81 km (calculated)[8]
24.233±0.004 h[9]
24.26±0.02 h[10]
0.057 (assumed)[8]


Orbit and classificationEdit

Erimomisaki is a non-family asteroid from the main belt's background population.[3] It orbits the Sun in the central main-belt at a distance of 1.7–3.8 AU once every 4 years and 7 months (1,678 days; semi-major axis of 2.76 AU). Its orbit has a relatively high eccentricity of 0.39 and an inclination of 12° with respect to the ecliptic.[2]

The body's observation arc begins with its first observation as 1984 YY2 at Crimea–Nauchnij in December 1984, more than 5 years prior to its official discovery observation at Kitami.[1]

Physical characteristicsEdit

Erimomisaki's spectral type is unknown.[3] The Collaborative Asteroid Lightcurve Link (CALL) generically assumes it to be a carbonaceous C-type asteroid (as its semi-major axis is larger than 2.7 AU).[8] However, based on the body's albedo (see below), it is rather a stony S-type asteroid.

Rotation periodEdit

In December 2007, two rotational lightcurve of Erimomisaki were obtained from photometric observations by international collaboration between astronomers Silvano Casulli, Russel Durkee, Caleb Boe, Fiona Vincent and David Higgins.[9][10] Lightcurve analysis gave a longer-than-average rotation period of 24.233 and 24.26 hours with a brightness amplitude of 0.42 and 0.27 magnitude, respectively (U=2/3-). CALL adopts the longer period as its best result.[8] While not being a slow rotator, Erimomisaki's period is longer than that of most other asteroids, which have spin rates between 2 and 20 hours.

Diameter and albedoEdit

According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Erimomisaki measures between 9.208 and 10.57 kilometers in diameter and its surface has an albedo between 0.2018 and 0.253.[4][5][6][7] CALL generically assumes a carbonaceous albedo of 0.057 and consequently calculates a much larger diameter of 16.81 kilometers based on an absolute magnitude of 12.6.[8]


This minor planet was named after Cape Erimo (Japanese: Erimo-misaki) at the south end of Hokkaidō, Japan. The official naming citation was published by the Minor Planet Center on 1 September 1993 (M.P.C. 22508).[12]


  1. ^ a b c d e f "5331 Erimomisaki (1990 BT1)". Minor Planet Center. Retrieved 15 May 2018.
  2. ^ a b c d "JPL Small-Body Database Browser: 5331 Erimomisaki (1990 BT1)" (2018-04-23 last obs.). Jet Propulsion Laboratory. Retrieved 15 May 2018.
  3. ^ a b c "Asteroid 5331 Erimomisaki". Small Bodies Data Ferret. Retrieved 15 May 2018.
  4. ^ a b c Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Dailey, J.; et al. (November 2011). "Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters". The Astrophysical Journal. 741 (2): 20. arXiv:1109.4096. Bibcode:2011ApJ...741...68M. doi:10.1088/0004-637X/741/2/68.
  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". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. (catalog)
  6. ^ a b c d Masiero, Joseph R.; Nugent, C.; Mainzer, A. K.; Wright, E. L.; Bauer, J. M.; Cutri, R. M.; et al. (October 2017). "NEOWISE Reactivation Mission Year Three: Asteroid Diameters and Albedos". The Astronomical Journal. 154 (4): 10. arXiv:1708.09504. Bibcode:2017AJ....154..168M. doi:10.3847/1538-3881/aa89ec.
  7. ^ a b c d Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. Retrieved 15 May 2018. Online catalog
  8. ^ a b c d e f g h "LCDB Data for (5331) Erimomisaki". Asteroid Lightcurve Database (LCDB). Retrieved 15 May 2018.
  9. ^ a b Behrend, Raoul. "Asteroids and comets rotation curves – (5331) Erimomisaki". Geneva Observatory. Retrieved 15 May 2018.
  10. ^ a b Boe, Caleb; Durkee, Russell I.; Casulli, Silvano; Vincent, Fiona; Higgins, David (October 2008). "The Lightcurve of Asteroid 5331 Erimomisaki". The Minor Planet Bulletin. 35 (4): 143. Bibcode:2008MPBu...35..143B. ISSN 1052-8091.
  11. ^ 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.
  12. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 15 May 2018.

External linksEdit