# 917 Lyka
**917 Lyka** is a main-belt asteroid, roughly 30 km across, that was discovered on 5 September 1915 by the astronomer G. N. Neujmin at the Simeis Observatory and carries the provisional designation 1915 S4.[1](https://astronomia.zcu.cz/planety/planetka-917) It is a dark, X-type body with a rotation period of about 7.88 hours, and its diameter has been measured both by stellar occultations and by thermal-radiometry estimates.[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family)
| Key fact | Detail |
|---|---|
| Discovery | 5 September 1915 by G. N. Neujmin at Simeis; provisional designation 1915 S4[1](https://astronomia.zcu.cz/planety/planetka-917) |
| Name origin | Named after a girl-friend of the sister of the discoverer, per N. S. Chernykh[3](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf) |
| Orbit | Semimajor axis 2.3815 au, eccentricity 0.2002, inclination 5.1243°, orbital period 3.675 years[1](https://astronomia.zcu.cz/planety/planetka-917) |
| Distance range | Perihelion 1.905 au, aphelion 2.858 au[1](https://astronomia.zcu.cz/planety/planetka-917) |
| Size | 35.61 ± 0.135 km with geometric albedo 0.043 (occultation-based value); JPL lists 34.878 ± 0.184 km from H = 11.6[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family) • [4](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf) |
| Rotation | Synodic period about 7.88 hours, lightcurve amplitude around 0.11 to 0.14 mag[4](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf) |
| Spectral class | X type[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family) |
## Discovery and naming
The asteroid was found at Simeis, on the Crimean coast, on 5 September 1915, and received the provisional designation 1915 S4 before being cataloged as minor planet number 917.[1](https://astronomia.zcu.cz/planety/planetka-917) The *Dictionary of Minor Planet Names* records that it was named after a girl-friend of the sister of the discoverer, citing the astronomer N. S. Chernykh as the source of that account.[3](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)
## Orbit
Lyka orbits in the main asteroid belt with a semimajor axis of 2.3815 au and an eccentricity of 0.2002, so its distance from the Sun ranges from 1.905 au at perihelion to 2.858 au at aphelion.[1](https://astronomia.zcu.cz/planety/planetka-917) One orbit takes 3.675 years, or 1,342.3 days, and the orbit is inclined 5.1243° to the ecliptic.[1](https://astronomia.zcu.cz/planety/planetka-917) Its Tisserand parameter with respect to Jupiter is 3.5, a value typical of main-belt rather than comet-like orbits.[1](https://astronomia.zcu.cz/planety/planetka-917)
The observation record is long: as of May 2026 the [Minor Planet Center](https://www.edgepedia.org/minor-planet-center) data used by the Czech Planetky project list 9,383 observations across 52 oppositions, with the asteroid observed every year from 1926 to 2026.[1](https://astronomia.zcu.cz/planety/planetka-917) An astrometric solution prepared for the 2010 occultation used 1,066 observations spanning 30 August 1926 to 26 March 2010, with 54 rejected.[5](https://www.occultations.org.nz/planet/2010/updates/100415_917_20783_u.htm)
## Physical properties
**Size and albedo.** Published diameters differ with method. The JPL Small-Bodies Database Browser lists a diameter of 34.878 ± 0.184 km based on an absolute magnitude H of 11.6 (JPL, 2019).[4](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf) A study of the inner main-belt primordial family, drawing on the Minor Planet Physical Properties Catalogue, gives 35.61 ± 0.135 km with a geometric visible albedo of 0.043 and an X spectral class, citing Lazzaro et al. (2004).[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family) [Occultation](https://www.edgepedia.org/occultation) chords from a 2005 event give a triaxial outline of 28 ± 4, 31 ± 1, and 30 ± 3 km.[6](https://www.asteroidoccultation.com/observations/Asteroid_Dimensions_from_Occultations.html) Occultation predictions in 2010 and 2023 used a rounder 28 km figure, the latter citing the astorb catalog's mean diameter of 28.1 km.[5](https://www.occultations.org.nz/planet/2010/updates/100415_917_20783_u.htm) • [7](https://astro.kretlow.de/cora/events/sodis/2023-05-03/UCAC4%20584-027327/%28917%29%20Lyka/) The albedo of 0.043 places Lyka among the dark main-belt surfaces.[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family)
**Rotation.** Several independent photometric campaigns converge on a synodic rotation period just under 7.9 hours. Bernasconi (2005) obtained 7.8672 ± 0.0055 h and Conjat (2018) 7.883 ± 0.0003 h, values published through Behrend's (2018) web compilation.[4](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf) Observations from Znith Observatory on 2018 October 26 and 30 and November 7 and 22 gave 7.881 ± 0.002 h with an amplitude of 0.14 mag, consistent with both earlier results.[4](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf) An OBAS campaign over 2018 October 3 to 5 found 7.889 ± 0.007 h with an amplitude of 0.11 mag, and classified Lyka in the Erigone group in the Warner et al. family scheme.[8](https://mpbulletin.org/issues/MPB_46-2.pdf) A shape-modeling study of a 4 Gyr collisional family derived a new shape solution for Lyka, listing a period of 7.88167 h and identifying it as a prograde rotator with ecliptic pole coordinates of λ = 44°, β = 49°.[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family)
## Occultations
Because Lyka is large enough to hide a star for several seconds, it has been a recurring occultation target. On 2010 April 15 UT it occulted an 11.3-magnitude star in Scorpius along a path across Australia from Innisfail in northern [Queensland](https://www.edgepedia.org/queensland) to Port Hedland in [Western Australia](https://www.edgepedia.org/western-australia); the combined light was predicted to drop 3.6 mag to 14.9 for at most 6.2 seconds, with the asteroid's shadow moving at 4.5434 km/s and a projected path width of about 29 km.[5](https://www.occultations.org.nz/planet/2010/updates/100415_917_20783_u.htm) A second 2010 event on August 30 crossed Western Australia near Margaret River and Bunbury, occulting a 9.8-magnitude star.[9](https://www.occultations.org.nz/planet/2010/updates/100830_917_22286_u.htm) On 2023 May 3, observers in the Czech Republic recorded a occultation of UCAC4 584-027327, with reported chord durations of 0.53 and 0.78 seconds corresponding to chord lengths of 18.9 and 27.8 km.[7](https://astro.kretlow.de/cora/events/sodis/2023-05-03/UCAC4%20584-027327/%28917%29%20Lyka/)
## Relation to other asteroids
A study of the source region of asteroid [162173 Ryugu](https://www.edgepedia.org/162173-ryugu) (1999 JU3) compared Ryugu's spectrum with candidate source populations and included 917 Lyka among the comparison objects, finding that the available spectral and color information favored a background source over the Polana family.[10](https://www.researchgate.net/publication/258305515_THE_ORIGIN_OF_ASTEROID_162173_1999_JU3) The spin-state study cited above treats Lyka as a member of an ancient inner main-belt collisional family and lists it among the prograde rotators of that group.[2](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family)
## References
1. [Planetka Lyka (917), Planety sluneční soustavy, University of West Bohemia](https://astronomia.zcu.cz/planety/planetka-917)
2. [Asteroid spin-states of a 4 Gyr collisional family, Astronomy & Astrophysics](https://www.researchgate.net/publication/362292094_Asteroid_spin-states_of_a_4_Gyr_collisional_family)
3. [Lutz D. Schmadel, Dictionary of Minor Planet Names, 5th edition](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)
4. [Brincat, Galdies, Stone, Grech (2019). Photometric observations of main-belt asteroids 917 Lyka, 5703 Hevelius, (6638) 1989 CA and 8073 Johnharmon. The Minor Planetary Bulletin, 46, 230-232.](https://www.um.edu.mt/library/oar/bitstream/123456789/44896/1/Brincat%2C%20Galdies%2C%20Stone%2C%20Grech%20%282019%29%20MPB%2046.pdf)
5. [RASNZ Occultation Section, Lyka occultation update, 2010 April 15](https://www.occultations.org.nz/planet/2010/updates/100415_917_20783_u.htm)
6. [Asteroid Dimensions from Occultations, asteroidoccultation.com](https://www.asteroidoccultation.com/observations/Asteroid_Dimensions_from_Occultations.html)
7. [Cora Occultation archive: 2023-05-03 / UCAC4 584-027327 / (917) Lyka](https://astro.kretlow.de/cora/events/sodis/2023-05-03/UCAC4%20584-027327/%28917%29%20Lyka/)
8. [OBAS lightcurves of eleven main-belt asteroids, Minor Planet Bulletin 46(2)](https://mpbulletin.org/issues/MPB_46-2.pdf)
9. [RASNZ Occultation Section, Lyka occultation update, 2010 August 30](https://www.occultations.org.nz/planet/2010/updates/100830_917_22286_u.htm)
10. [The origin of asteroid 162173 (1999 JU3)](https://www.researchgate.net/publication/258305515_THE_ORIGIN_OF_ASTEROID_162173_1999_JU3)
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*Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Main-belt asteroids and numbered minor planets › Middle-belt asteroids › Asteroids named for people*
*Initially written Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license