950 Ahrensa

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950 Ahrensa
Discovery [1]
Discovered by K. Reinmuth
Discovery site Heidelberg Obs.
Discovery date 1 April 1921
MPC designation 950 Ahrensa
Named after
Ahrens family
(friends of discoverer)[2]
1921 JP · 1955 SU2
1974 VG3 · A904 RF
main-belt · Phocaea[3]
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc 111.60 yr (40761 days)
Aphelion 2.7477 AU (411.05 Gm)
Perihelion 1.9958 AU (298.57 Gm)
2.3717 AU (354.80 Gm)
Eccentricity 0.15851
3.65 yr (1334.1 d)
0° 16m 11.424s / day
Inclination 23.477°
Earth MOID 1.00255 AU (149.979 Gm)
Jupiter MOID 2.22677 AU (333.120 Gm)
Jupiter Tisserand parameter 3.417
Physical characteristics
Dimensions 15.03±1.8 (IRAS:15) km[4]
16.21±0.53 km[5]
14.299±0.070 km[6]
16.66±0.41 km[7]
15.34 km (derived)[3]
Mean radius
7.515±0.9 km
202±1 h,[8] 202 h (8.4 d)[1]
0.1793±0.054 (IRAS:15)[1][4]
0.2727 (derived)[3]

950 Ahrensa, provisional designation 1921 JP, is a stony asteroid and slow rotator from the inner regions of the asteroid belt, about 15 kilometers in diameter. It was discovered on 1 April 1921, by German astronomer Karl Reinmuth at Heidelberg Observatory in southern Germany.[9]

The S-type asteroid, classified as a Sa-subtype in the SMASS taxonomic scheme, is a member of the Phocaea family, a group of asteroids with similar orbital characteristics. It orbits the Sun at a distance of 2.0–2.7 AU once every 3 years and 8 months (1,334 days). Its orbit shows an eccentricity of 0.16 and is tilted by 23 degrees to the plane of the ecliptic.

A photometric light-curve analysis at the U.S. Palmer Divide Observatory in 2009, showed that the body has an exceptionally long rotation period of 202 hours.[8] According to the surveys carried out by the Infrared Astronomical Satellite, IRAS, the Japanese Akari satellite, and the U.S. Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the surface of the asteroid has an albedo in the range of 0.16 to 0.23, while the Collaborative Asteroid Lightcurve Link derives an even higher value of 0.27 for the stony body.[3][4][5][6][7]

The minor planet was named in honor of friends of the discoverer Karl Reinmuth, the Ahrens family, who helped him financially at the Heidelberg Observatory. Reinmuth also named the minor planet 909 Ulla after Ulla Ahrens, a member of this family.[2]


  1. ^ a b c d e "JPL Small-Body Database Browser: 950 Ahrensa (1921 JP)" (2015-10-30 last obs.). Jet Propulsion Laboratory. Retrieved 2 May 2016. 
  2. ^ a b Schmadel, Lutz D. (2003). Dictionary of Minor Planet Names – (950) Ahrensa. Springer Berlin Heidelberg. p. 84. ISBN 978-3-540-29925-7. Retrieved 4 January 2016. 
  3. ^ a b c d e "LCDB Data for (950) Ahrensa". Asteroid Lightcurve Database (LCDB). Retrieved 4 January 2016. 
  4. ^ a b c Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. Bibcode:2004PDSS...12.....T. Retrieved 4 January 2016. 
  5. ^ a b c 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 4 January 2016. 
  6. ^ a b c 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:1109.6407free to read. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved 4 January 2016. 
  7. ^ a b c 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:1209.5794free to read. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 4 January 2016. 
  8. ^ a b Warner, Brian D. (January 2010). "Asteroid Lightcurve Analysis at the Palmer Divide Observatory: 2009 June-September". The Minor Planet Bulletin. 37 (1): 24–27. Bibcode:2010MPBu...37...24W. ISSN 1052-8091. Retrieved 4 January 2016. 
  9. ^ "950 Ahrensa (1921 JP)". Minor Planet Center. Retrieved 4 January 2016. 

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