896 Sphinx

896 Sphinx /ˈsfɪŋks/ is a background asteroid from the inner regions of the asteroid belt, that measures approximately 13 kilometers (8 miles) in diameter. It was discovered on 1 August 1918, by astronomer Max Wolf at the Heidelberg-Königstuhl State Observatory in southwest Germany.[1] The asteroid has a rotation period of 21.0 hours and is one of few low-numbered objects for which no spectral type has been determined. It was named after the Sphinx, a creature from Greek and Egyptian mythology.[2]

896 Sphinx
Modelled shape of Sphinx from its lightcurve
Discovery [1]
Discovered byM. F. Wolf
Discovery siteHeidelberg Obs.
Discovery date1 August 1918
Designations
(896) Sphinx
Pronunciation/ˈsfɪŋks/
Named after
A918 PE · 1918 DV
AdjectivesSphinxian /ˈsfɪŋksiən/[6]
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc101.50 yr (37,074 d)
Aphelion2.6588 AU
Perihelion1.9128 AU
2.2858 AU
Eccentricity0.1632
3.46 yr (1,262 d)
211.73°
0° 17m 6.72s / day
Inclination8.1903°
254.18°
1.9628°
Physical characteristics
Mean diameter
  • 11.974±0.071 km[7]
  • 13.07±0.5 km[8]
  • 14.45±0.35 km[9]
21.038±0.008 h[10]
  • (172.0°, 20.0°) (λ1/β1)[5]
  • (352.0°, 42.0°) (λ2/β2)[5]
  • 0.163±0.009[9]
  • 0.1971±0.017[8]
  • 0.242±0.045[7]
n.a.
11.6[1][3]

    Orbit and classification

    Sphinx is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.[4][5] It orbits the Sun in the inner asteroid belt at a distance of 1.9–2.7 AU once every 3 years and 6 months (1,262 days; semi-major axis of 2.29 AU). Its orbit has an eccentricity of 0.16 and an inclination of 8° with respect to the ecliptic.[3] The body's observation arc begins at Heidelberg Observatory on 9 October 1918, two months after its official discovery observation.[1]

    Naming

    This minor planet was named after the Sphinx, a legendary creature from Greek and Egyptian mythology. The female monster has the head of a woman, the haunches of a lion, and the wings of a bird. It has the habit of killing anyone who cannot answer her riddle. The naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 87).[2]

    Physical characteristics

    Contrary to most other low-numbered asteroids, no spectral type has been determined.[5][11] Based on its relatively high albedo (see below) and its location within the inner parts of the main-belt, Sphinx may possibly be a common, stony S-type asteroid.

    Rotation period

    In June 2018, a rotational lightcurve of Sphinx was obtained from photometric observations by Tom Polakis at the Command Module Observatory (V02) in Arizona. Lightcurve analysis gave a rotation period of 21.038±0.008 hours with a brightness variation of 0.16±0.02 magnitude (U=2+). However, an alternative period solution of 10.541±0.003 hours with an amplitude of 0.17±0.02 magnitude is also possible.[10] Both results supersede a tentative period determination by Laurent Bernasconi from September 2001 (U=1).[12]

    A modeled lightcurve using photometric data from the Lowell Photometric Database and from the Wide-field Infrared Survey Explorer (WISE) was published in 2018. It gave a divergent sidereal period of 12.95209±0.00002 hours and includes two spin axes at (172.0°, 20.0°) and (352.0°, 42.0°) in ecliptic coordinates (λ, β).[13]

    Diameter and albedo

    According to the surveys carried out by the NEOWISE mission of NASA's WISE telescope, the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Sphinx measures (11.974±0.071), (13.07±0.5) and (14.45±0.35) kilometers in diameter and its surface has an albedo of (0.242±0.045), (0.1971±0.017) and (0.163±0.009), respectively.[7][8][9] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2332 and a diameter of 13.17 kilometers based on an absolute magnitude of 11.6.[11] Alternative mean-diameter measurements published by the WISE team include (12.59±2.11 km), (13.320±0.122 km) and (13.658±3.101 km) with corresponding albedos of (0.25±0.11), (0.1924±0.0127) and (0.241±0.080).[5][11]

    References
    1. "896 Sphinx (A918 PE)". Minor Planet Center. Retrieved 25 February 2020.
    2. Schmadel, Lutz D. (2007). "(896) Sphinx". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 81. doi:10.1007/978-3-540-29925-7_897. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 896 Sphinx (A918 PE)" (2020-02-01 last obs.). Jet Propulsion Laboratory. Retrieved 25 February 2020.
    4. "Asteroid 896 Sphinx – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 25 February 2020.
    5. "Asteroid 896 Sphinx". Small Bodies Data Ferret. Retrieved 25 February 2020.
    6. "Sphinx". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
    7. Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121.
    8. Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 25 February 2020.
    9. 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 25 February 2020. (online, AcuA catalog p. 153)
    10. Polakis, Tom (October 2018). "Lightcurve Analysis for Fourteen Main-belt Minor Planets" (PDF). Minor Planet Bulletin. 45 (4): 347–352. Bibcode:2018MPBu...45..347P. ISSN 1052-8091.
    11. "LCDB Data for (896) Sphinx". Asteroid Lightcurve Database (LCDB). Retrieved 25 February 2020.
    12. Behrend, Raoul. "Asteroids and comets rotation curves – (896) Sphinx". Geneva Observatory. Retrieved 25 February 2020.
    13. Ďurech, J.; Hanuš, J.; Alí-Lagoa, V. (September 2018). "Asteroid models reconstructed from the Lowell Photometric Database and WISE data". Astronomy and Astrophysics. 617: A57. arXiv:1807.02083. Bibcode:2018A&A...617A..57D. ISSN 0004-6361.
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