12923 Zephyr

12923 ZephyrDiscovery[1]

Discovered by| LONEOS
Discovery site| Anderson Mesa Stn.
Discovery date| 11 April 1999
Designations

MPC designation

| (12923) Zephyr
Pronunciation| /ˈzɛfər/[4]
Named after| Zephyrus[2]
(Greek mythology)

Alternative designations

| 1999 GK4
Minor planet category|

* NEO
* Apollo[1][3]
* PHA[1][3]

Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc| 61.75 yr (22,554 days)
Earliest precovery date| 21 April 1955
|{{{apsis}}}|helion}}| 2.9267 AU
|{{{apsis}}}|helion}}| 0.9964 AU

Semi-major axis

| 1.9615 AU
Eccentricity| 0.4920
Orbital period| 2.75 yr (1,003 days)
Mean anomaly| 199.23°
Mean motion| 0° 21m 31.68s / day
Inclination| 5.3045°
Longitude of ascending node| 168.21°

|{{{apsis}}}|helion}}

| 147.06°
Earth MOID| 0.0211 AU (8.2 LD)
Physical characteristics
Mean diameter|

* 1.86±0.46 km[5]
* 2.060±0.013 km[6][7]
* 2.062 km[8]

Rotation period| 3.891 h[lower-alpha 1]
Geometric albedo|

* 0.1764[8]
* 0.199±0.034[6][7]
* 0.20±0.16[9]
* 0.21±0.17[5]

Spectral type

* SMASS = S:[1]
* S[10][11]

Absolute magnitude (H)|

* 15.40±0.1 (R)[lower-alpha 1]
* 15.77±0.24[12]
* 15.8[1][7]
* 15.93±0.078[8][11]

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]

## Contents

* 1 Orbit and classification
* 1.1 Close encounters
* 2 Naming
* 3 Physical characteristics
* 3.1 Rotation period
* 3.2 Diameter and albedo
* 4 Notes
* 5 References
* 6 External links

## Orbit and classification

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

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]

## Naming

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

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

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 ({{{1}}}).[lower-alpha 1]

### Diameter and albedo

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]

## Notes

1. ↑ 1.0 1.1 1.2 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)

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 "JPL Small-Body Database Browser: 12923 Zephyr (1999 GK4)". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012923. Retrieved 17 October 2017.
2. ↑ 2.0 2.1 2.2 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. ↑ 3.0 3.1 3.2 3.3 "12923 Zephyr (1999 GK4)". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=12923. Retrieved 17 October 2017.
4. ↑ zephyr (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=zephyr (Subscription or UK public library membership required.)
5. ↑ 5.0 5.1 5.2 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". The Astronomical Journal 141 (3): 10. doi:10.1088/0004-6256/141/3/75. Bibcode: 2011AJ....141...75H. https://authors.library.caltech.edu/22857/1/Harris2011p13012Astron_J.pdf.
6. ↑ 6.0 6.1 6.2 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. doi:10.1088/0004-637X/743/2/156. Bibcode: 2011ApJ...743..156M.
7. ↑ 7.0 7.1 7.2 7.3 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. doi:10.1088/0004-637X/741/2/90. Bibcode: 2011ApJ...741...90M.
8. ↑ 8.0 8.1 8.2 8.3 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. doi:10.1016/j.icarus.2012.07.026. Bibcode: 2012Icar..221..365P.
9. ↑ 9.0 9.1 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. doi:10.1088/0004-6256/142/3/85. Bibcode: 2011AJ....142...85T.
10. ↑ 10.0 10.1 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. doi:10.1016/j.icarus.2013.10.004. Bibcode: 2014Icar..228..217T.
11. ↑ 11.0 11.1 11.2 11.3 "LCDB Data for (12923) Zephyr". Asteroid Lightcurve Database (LCDB). http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=12923|Zephyr. 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. doi:10.1016/j.icarus.2015.08.007. Bibcode: 2015Icar..261...34V.
13. ↑ "MPC/MPO/MPS Archive". Minor Planet Center. https://www.minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html. Retrieved 17 October 2017.

## External links

* (12923) Zephyr at NEODyS-2
* Asteroid Lightcurve Database (LCDB), query form (info )
* Dictionary of Minor Planet Names, Google books
* Asteroids and comets rotation curves, CdR - Observatoire de Genève, Raoul Behrend
* 12923 Zephyr at NeoDyS-2, Near Earth Objects—Dynamic Site
* Ephemeris * Obs prediction * Orbital info * MOID * Proper elements * Obs info * Close * Physical info * NEOCC
* 12923 Zephyr at ESA–space situational awareness
* Ephemerides * Observations * Orbit * Physical Properties * Summary
* 12923 Zephyr at the JPL Small-Body Database
* Close approach * Discovery * Ephemeris * Orbit diagram * Orbital elements * Physical parameters

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