79360 Sila–Nunam

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Discovered by Jane X. Luu, David C. Jewitt,
Chadwick A. Trujillo, Jun Chen[1]
Discovery date 3 February 1997
MPC designation 79360 Sila–Nunam
1997 CS29
Minor planet category TNO (cubewano)[2][3]
Adjectives Silapian, Nunamian
Orbital characteristics[5]
Epoch JD 2457000.5 (9 December 2014)
Aphelion 44.877 AU
Perihelion 43.418 AU
44.148 AU
Eccentricity 0.01652
293.34 a (107,140 d)
Inclination 2.23789°
Known satellites 1 at 2,780 ± 20 km (1,725 ± 10 mi)[4]
Physical characteristics
Dimensions ≈ 250 km or 155 mi (Sila)[4]
≈ 235 km or 146 mi (Nunam)[6][4]
(335 ± 85 km combined)[7]
Mass 1.08±0.02×1019 kg (combined)[4]
Mean density
Albedo 0.086+0.026
Temperature ~42 K (−384 °F)
Spectral type
21.54–21.78 (2014–2015)
(combined) 5.5,[8]
(individual) 6.2 & 6.3 (diff. = 0.12),[4]

79360 Sila–Nunam is a double classical Kuiper belt object (cubewano) with components of almost equal size, orbiting beyond Neptune in the Solar System. The name of the system is the combined names of the two bodies, Sila and Nunam.[6]

Discovery and name[edit]

Sila–Nunam was discovered on 3 February 1997 by Jane X. Luu, David C. Jewitt, Chad Trujillo, and Jun Chen at the Mauna Kea Observatory, Hawaii, and given the provisional designation 1997 CS29. It was resolved as a binary system in Hubble observations of 22 October 2002 by Denise C. Stephens and Keith S. Noll and announced, under the designation S/2005 (79360) 1, on 5 October 2005.

The two components are named after Inuit deities. Sila "spirit" is the Inuit god of the sky, weather, and life force. Nunam "earth" is the Earth goddess, in some traditions Sila's wife. Nunam created the land animals and, in some traditions, the Inuit people (in other traditions Sila created the first people out of wet sand). Sila breathed life into the Inuit.[5]


Sila–Nunam is a dynamically cold classical system (cubewano). It orbits very close to 4:7 mean-motion resonance with Neptune.[7]

Physical characteristics[edit]

In 2010, thermal flux from Sila–Nunam in the far-infrared was measured by the Herschel Space Telescope. As a result its size, while it was assumed to be a single body, was estimated to lie within the range 250 to 420 km (155 to 260 mi).[7] Now that it is known to be a binary system, one body 95% the size of the other, the diameters are estimated to be 243 and 230 kilometres (151 and 143 mi).

Sila–Nunam is very red in visible light and has a flat featureless spectrum in the near-infrared.[9][10] There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion.[11]

Double system[edit]

Sila and Nunam are so close in size (within 5%) that they may be thought of as a double cubewano. Sila is approximately 243 km in diameter and Nunam 230 km. They orbit at a distance of 2,780 ± 20 km (1,727 ± 12 mi) every 12.51 days:[4]

Semi-major axis:  2,780 ± 20 km
Orbital period: 12.509 9 ± 0.000 4 d
Eccentricity: 0.02 ± 0.02°
Inclination: 103.5 ± 0.4°

Each has apparently been resurfaced with ejecta from impacts on the other.[12]


  1. ^ "List Of Transneptunian Objects". IAU Minor Planet Center. Archived from the original on 19 August 2010. Retrieved 2 August 2010. 
  2. ^ "MPEC 2009-R09 :Distant Minor Planets (2009 SEPT. 16.0 TT)". IAU Minor Planet Center. 4 September 2009. Retrieved 4 October 2009. 
  3. ^ Marc W. Buie (2 February 2009 using 142 observations). "Orbit Fit and Astrometric record for 79360". SwRI (Space Science Department). Retrieved 4 October 2009.  Check date values in: |date= (help)
  4. ^ a b c d e f g h i j k l m n o p "(79360) Sila-Nunam". Wm. Robert Johnston. 11 January 2012. Retrieved 12 January 2012. 
  5. ^ a b c "JPL Small-Body Database Browser: 79360 Sila-Nunam (1997 CS29)". 2014-01-28 last obs. Retrieved 2014-11-17.  Check date values in: |date= (help)
  6. ^ a b Sila – Nunam Mutual Events (Lowell)
  7. ^ a b c Muller, T.G.; Lellouch, E.; Stansberry, J. et al. (2010). ""TNOs are Cool": A survey of the trans-Neptunian region I. Results from the Herschel science demonstration phase (SDP)". Astronomy and Astrophysics 518: L146. arXiv:1005.2923. Bibcode:2010A&A...518L.146M. doi:10.1051/0004-6361/201014683. 
  8. ^ a b c Stephen C. Tegler. "Kuiper Belt Object Magnitudes and Surface Color". Retrieved 1 August 2010. 
  9. ^ Grundy, W.M.; Buie, M.W.; Spencer, J. R. (2005). "Near-Infrared Spectrum of Low-Inclination Classical Kuiper Belt Object (79360) 1997 CS29". The Astronomical Journal 130 (3): 1299–1301. Bibcode:2005AJ....130.1299G. doi:10.1086/431958. 
  10. ^ Fornasier, S.; Barucci, M.A.; de Bergh, C. at al. (2009). "Visible spectroscopy of the new ESO large programme on trans-Neptunian objects and Centaurs: final results". Astronomy and Astrophysics 508 (1): 457–465. arXiv:0910.0450. Bibcode:2009A&A...508..457F. doi:10.1051/0004-6361/200912582. 
  11. ^ Boehnhardt, H.; Bagnulo, S.; Muinonen, S. at al. (2004). "Surface characterization of 28978 Ixion (2001 KX76)". Astronomy and Astrophysics 415 (2): L21–L25. Bibcode:2004A&A...415L..21B. doi:10.1051/0004-6361:20040005. 
  12. ^ Rabinowitz, et al. (2009). "Evidence for Recent Resurfacing of the Binary Kuiper Belt Object 1997 CS29".