12923 Zephyr

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12923 Zephyr
Discovered byLONEOS
Discovery siteAnderson Mesa Stn.
Discovery date11 April 1999
(12923) Zephyr
Named after
(Greek mythology)
1999 GK4
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc61.75 yr (22,554 days)
Earliest precovery date21 April 1955
Aphelion2.9267 AU
Perihelion0.9964 AU
1.9615 AU
2.75 yr (1,003 days)
0° 21m 31.68s / day
Earth MOID0.0211 AU (8.2 LD)
Physical characteristics
Mean diameter
3.891 h[a]

12923 Zephyr (prov. designation: 1999 GK4) is a stony asteroid, classified as potentially hazardous asteroid and near-Earth object of the Apollo group, approximately 2 kilometers (1.2 miles) in diameter. It was discovered on 11 April 1999, by astronomers of the Lowell Observatory Near-Earth Object Search at Anderson Mesa Station near Flagstaff, Arizona.[3] The asteroid was named after the deity Zephyrus from Greek mythology.[2]

Orbit and classification[edit]

Zephyr orbits the Sun at a distance of 1.0–2.9 AU once every 2 years and 9 months (1,003 days). Its orbit has an eccentricity of 0.49 and an inclination of 5° with respect to the ecliptic.[1] The body's observation arc begins with a precovery taken at Palomar Observatory in April 1955, almost 44 years prior to its official discovery observation at Anderson Mesa.[3]

Close encounters[edit]

This near-Earth asteroid has an Earth minimum orbital intersection distance of 0.0211 AU (3,160,000 km), which corresponds to 8.2 lunar distances.[1] This short distance as well as its sufficiently large size makes it a potentially hazardous asteroid. In September 2010, the asteroid approached Earth at 0.2546 AU (38,100,000 km); it will make close encounters with Earth again in 2021, 2032 and 2043.[1]


This minor planet was named after the god of the west wind, Zephyrus, from Greek mythology. The name was suggested by M. Smitherman.[2] The official naming citation was published by the Minor Planet Center on 28 September 2004 (M.P.C. 52768).[13]

Physical characteristics[edit]

In the SMASS classification, Zephyr is a common S-type asteroid.[1] The body is also characterized as a stony asteroid by the Infrared Telescope Facility,[10] and in the Tholen classification (noisy spectrum).[11]

Rotation period[edit]

In April 1999, a rotational lightcurve of Zephyr was obtained from photometric observations by Czech astronomer Petr Pravec at Ondřejov Observatory. Lightcurve analysis gave a well-defined rotation period of 3.891 hours with a brightness amplitude of 0.18 magnitude (U=3).[a]

Diameter and albedo[edit]

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer and the ExploreNEOs survey of the Spitzer Space Telescope, Zephyr measures between 1.86 and 2.062 kilometers in diameter and its surface has an albedo between 0.1764 and 0.21.[5][6][7][8][9]

The Collaborative Asteroid Lightcurve Link adopts Petr Pravec's revised WISE data, with albedo of 0.1764 and a diameter of 2.06 kilometers based on an absolute magnitude of 15.93.[11]


  1. ^ a b c Pravec (1999) web: rotation period 3.891 hours with a brightness amplitude of 0.18 mag. Summary figures for (12923) Zephyr at LCDB and Ondrejov Asteroid Photometry Project (data sheet)


  1. ^ a b c d e f g h i j "JPL Small-Body Database Browser: 12923 Zephyr (1999 GK4)" (2017-01-19 last obs.). Jet Propulsion Laboratory. Retrieved 17 October 2017.
  2. ^ a b c Schmadel, Lutz D. (2006). "(12923) Zephyr [1.96, 0.49, 5.3]". Dictionary of Minor Planet Names – (12923) Zephyr, Addendum to Fifth Edition: 2003–2005. Springer Berlin Heidelberg. p. 76. doi:10.1007/978-3-540-34361-5_734. ISBN 978-3-540-34361-5.
  3. ^ a b c d "12923 Zephyr (1999 GK4)". Minor Planet Center. Retrieved 17 October 2017.
  4. ^ "zephyr". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  5. ^ a b c Harris, A. W.; Mommert, M.; Hora, J. L.; Mueller, M.; Trilling, D. E.; Bhattacharya, B.; et al. (March 2011). "ExploreNEOs. II. The Accuracy of the Warm Spitzer Near-Earth Object Survey" (PDF). The Astronomical Journal. 141 (3): 10. Bibcode:2011AJ....141...75H. doi:10.1088/0004-6256/141/3/75.
  6. ^ a b c Mainzer, A.; Grav, T.; Bauer, J.; Masiero, J.; McMillan, R. S.; Cutri, R. M.; et al. (December 2011). "NEOWISE Observations of Near-Earth Objects: Preliminary Results". The Astrophysical Journal. 743 (2): 17. arXiv:1109.6400. Bibcode:2011ApJ...743..156M. doi:10.1088/0004-637X/743/2/156.
  7. ^ 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.
  8. ^ 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.
  9. ^ a b Thomas, C. A.; Trilling, D. E.; Emery, J. P.; Mueller, M.; Hora, J. L.; Benner, L. A. M.; et al. (September 2011). "ExploreNEOs. V. Average Albedo by Taxonomic Complex in the Near-Earth Asteroid Population". The Astronomical Journal. 142 (3): 12. Bibcode:2011AJ....142...85T. doi:10.1088/0004-6256/142/3/85.
  10. ^ a b Thomas, Cristina A.; Emery, Joshua P.; Trilling, David E.; Delbó, Marco; Hora, Joseph L.; Mueller, Michael (January 2014). "Physical characterization of Warm Spitzer-observed near-Earth objects". Icarus. 228: 217–246. arXiv:1310.2000. Bibcode:2014Icar..228..217T. doi:10.1016/j.icarus.2013.10.004.
  11. ^ a b c d "LCDB Data for (12923) Zephyr". Asteroid Lightcurve Database (LCDB). Retrieved 17 October 2017.
  12. ^ 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.
  13. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 17 October 2017.

External links[edit]