(153591) 2001 SN263

(153591) 2001 SN263 is a carbonaceous trinary[3] asteroid, classified as near-Earth object and former potentially hazardous asteroid of the Amor group, approximately 2.6 kilometers (1.6 miles) in diameter. It was discovered by the Lincoln Near-Earth Asteroid Research project at Lincoln Lab's Experimental Test Site in Socorro, New Mexico, on 20 September 2001.[1] The two synchronous minor-planet moons measure approximately 770 and 430 meters and have an orbital period of 16.46 and 150 hours, respectively.[4][10]

(153591) 2001 SN263
Radar image of 2001 SN263 and its two satellites imaged by the Arecibo Observatory in 2008
Discovery [1]
Discovered byLINEAR
Discovery siteLincoln Lab's ETS
Discovery date20 September 2001
Designations
(153591) 2001 SN263
2001 SN263
NEO · Amor [1][2]
Orbital characteristics [2]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc25.18 yr (9,198 days)
Aphelion2.9368 AU
Perihelion1.0363 AU
1.9865 AU
Eccentricity0.4783
2.80 yr (1,023 days)
148.57°
0° 21m 7.2s / day
Inclination6.6853°
325.83°
172.86°
Known satellites2[3]
Earth MOID0.0520 AU · 20.3 LD
Physical characteristics
Mean diameter
2 km[3]
2.5±0.3 km[4]
2.6 km[5]
2.63±0.40 km[6]
Mass(917.5±2.2)×1010 kg[7]
Mean density
1.1±0.2 g/cm3[4]
3.20±0.01 h[8]
3.423±0.001 h[lower-alpha 1]
3.42510±0.00007 h[9]
3.4256±0.0002 h[4]
0.048±0.015[6]
C [8] · B [lower-alpha 2]
16.81[10] · 16.9[2]

    Numbering and naming

    This minor planet was numbered by the Minor Planet Center on 2 April 2007.[11] As of 2018, the primary and its moons have not been named.[1] In the scientific literature, the components of the trinary system are generically referred to as Alpha, Beta and Gamma, but these labels are not recognized by the IAU.[5][4]

    Primary

    2001 SN263, the primary object of this trinary system, is an unusual carbonaceous near-Earth asteroid of a C- or somewhat brighter B-type.[8][lower-alpha 2] It orbits the Sun at a distance of 1.0–2.9 AU once every 2 years and 10 months (1,023 days). Its orbit has an eccentricity of 0.48 and an inclination of 7° with respect to the ecliptic.[2] A first precovery was taken at Palomar Observatory during the Digitized Sky Survey in 1990, extending the body's observation arc by 11 years prior to its official discovery observation at Socorro.[1]

    It has an Earth minimum orbital intersection distance (MOID) of 0.0520 AU (7,780,000 km), which translates into 20.3 lunar distances.[2] With an Earth MOID above 0.05 AU, 2001 SN263 is no longer a potentially hazardous asteroid, but it was classified as such by the MPC until early 2017.[1][12]

    Radar observations show that it measures 2.5 kilometers in diameter.[4] Its surface has a low albedo of 0.048.[6] Rotational lightcurves obtained from photometric observations gave a rotation period of 3.423 hours (best result) with a brightness variation between 0.13 and 0.27 magnitude (U=2/3/3).[8][9][lower-alpha 1] Radar observations gave a concurring period of 3.4256 hours, and subsequent modeling of both radiometric and photometric observations gave a spin axis of (309.0°, −80.0°) in ecliptic coordinates (λ, β).[4]

    Trinary system

    In 2008, scientists using the planetary radar at Arecibo Observatory discovered that the object is orbited by two satellites, when the triple asteroid made a close approach to Earth of 0.066 AU (nearly 10 million kilometers). The largest body (preliminarily called Alpha) is spheroid in shape, with principal axes of 2.8±0.1 km, 2.7±0.1 km, and 2.9±0.3 km, with an effective diameter of 2.5±0.3 km and a density of 1.1±0.2 g/cm3. The satellites, named Beta and Gamma, are several times smaller in size. Beta is 0.77±0.12 km in diameter and Gamma 0.43±0.14 km.[4]

    The only other unambiguously identified triple asteroids in the near-Earth population are (136617) 1994 CC, which was discovered to be a triple system in 2009, and 3122 Florence, which was found to be a triple system in September 2017.[13]

    Orbital characteristics of satellites

    The orbital properties of the satellites are listed in this table.[7] The orbital planes of both satellites are inclined relative to each other; the relative inclination is about 14 degrees. Such a large inclination is suggestive of past evolutionary events (e.g. close encounter with a terrestrial planet, mean-motion-resonance crossing) that may have excited their orbits from a coplanar configuration to an inclined state.

    NameMass (est.)Semi-major axisOrbital periodEccentricity
    Gamma (inner)10×1010 kg3.8 km0.686 days0.016
    Beta (outer)24×1010 kg16.6 km6.225 days0.015

    Exploration

    This triple asteroid system is the target for the planned ASTER mission scheduled for launch in 2021 by the Brazilian Space Agency.[14]

    Notes
    1. Warner (2011) web: lightcurve plot of (153591) 2001 SN263, Palmer Divide Observatory, Brian D. Warner (2008). Photometric observations from 20 February 2008: rotation period 3.423±0.001 hours with a brightness amplitude of 0.14±0.02 magnitude. Quality code: 3. Summary figures for all obtained lightcurves at Collaborative Asteroid Lightcurve Link (CALL) for (153591)
    2. Perna (2014): photometric observation from 24 June 2011: with a brightness amplitude of mag. Summary figures at Collaborative Asteroid Lightcurve Link (CALL) for (153591)

    References
    1. "153591 (2001 SN263)". Minor Planet Center. Retrieved 3 September 2017.
    2. "JPL Small-Body Database Browser: 153591 (2001 SN263)" (2015-12-01 last obs.). Jet Propulsion Laboratory. Retrieved 1 June 2017.
    3. Nolan, M. C.; Howell, E. S.; Benner, L. A. M.; Ostro, S. J.; Giorgini, J. D.; Busch, M. W.; et al. (February 2008). "(153591) 2001 SN_263". Central Bureau Electronic Telegrams (1254). Bibcode:2008CBET.1254....1N. Retrieved 22 March 2017.
    4. Becker, Tracy M.; Howell, Ellen S.; Nolan, Michael C.; Magri, Christopher; Pravec, Petr; Taylor, Patrick A.; et al. (March 2015). "Physical modeling of triple near-Earth Asteroid (153591) 2001 SN263 from radar and optical light curve observations" (PDF). Icarus. 248: 499–515. Bibcode:2015Icar..248..499B. doi:10.1016/j.icarus.2014.10.048. Retrieved 22 March 2017.
    5. Becker, Tracy; Howell, E. S.; Nolan, M. C.; Magri, C. (September 2008). "Physical Modeling of Triple Near-Earth Asteroid 153591 (2001 SN263)". American Astronomical Society. 40: 437. Bibcode:2008DPS....40.2806B. Retrieved 22 March 2017.
    6. Delbo, Marco; Walsh, Kevin; Mueller, Michael; Harris, Alan W.; Howell, Ellen S. (March 2011). "The cool surfaces of binary near-Earth asteroids". Icarus. 212 (1): 138–148. Bibcode:2011Icar..212..138D. doi:10.1016/j.icarus.2010.12.011. Retrieved 22 March 2017.
    7. Fang, Julia; Margot, Jean-Luc; Brozovic, Marina; Nolan, Michael C.; Benner, Lance A. M.; Taylor, Patrick A. (May 2011). "Orbits of Near-Earth Asteroid Triples 2001 SN263 and 1994 CC: Properties, Origin, and Evolution". The Astronomical Journal. 141 (5): 15. arXiv:1012.2154. Bibcode:2011AJ....141..154F. doi:10.1088/0004-6256/141/5/154. Retrieved 1 June 2017.
    8. Betzler, Alberto Silva; Novaes, Alberto Brum; Celedon, Julian Hermogenes Quesada (October 2008). "A Study of the Trinary NEA 2001 SN263". The Minor Planet Bulletin. 35 (4): 182–184. Bibcode:2008MPBu...35..182B. ISSN 1052-8091. Retrieved 22 March 2017.
    9. Oey, Julian (January 2009). "Lightcurve Analysis of Asteroids from Leura and Kingsgrove Observatories in the First Half of 2008". The Minor Planet Bulletin. 36 (1): 4–6. Bibcode:2009MPBu...36....4O. ISSN 1052-8091. Retrieved 22 March 2017.
    10. "LCDB Data for (153591)". Asteroid Lightcurve Database (LCDB). Retrieved 3 September 2017.
    11. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 24 February 2018.
    12. "153591 (2001 SN263)". Minor Planet Center. web.archive.org. 22 March 2017. Archived from the original on 22 March 2017. Retrieved 3 September 2017.
    13. "Radar Reveals Two Moons Orbiting Asteroid Florence". Jet Propulsion Laboratory. 1 September 2017.
    14. Development of a Solar Electric Propulsion System for the First Brazilian Deep Space Mission. José Leonardo Ferreira, Alexandre A. Martins, Rodrigo Andres Miranda, Helbert O. C. Junior, Alvaro Q. D. R. Silva, and Ivan Soares Ferreira, Alexander Sukhanov, Othon Cabo Winter. Presented at the 35th International Electric Propulsion Conference. IEPC-2017-166. Georgia Institute of Technology - Atlanta, Georgia, USA. October 8–12, 2017.
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