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79360 Sila–Nunam

Sila–Nunam imaged by the Hubble Space Telescope in 2004
Discovery
Discovered by	J. X. Luu D. C. Jewitt C. A. Trujillo J. Chen
Discovery site	Mauna Kea Obs.
Discovery date	4 February 1997
Designations
MPC designation	(79360) Sila–Nunam
Pronunciation	/ˈsiːlə ˈnuːnəm/
Alternative designations	1997 CS29
Minor planet category	TNO (cubewano)
Adjectives	Silaupian, Nunaupian
Orbital characteristics
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc	6940 days (19.00 yr)
Aphelion	44.8452 AU (6.70875 Tm)
Perihelion	43.3862 AU (6.49048 Tm)
Semi-major axis	44.1157 AU (6.59961 Tm)
Eccentricity	0.016536
Orbital period (sidereal)	293.02 yr (107026 d)
Mean anomaly	331.884°
Mean motion	0.00336367°/day
Inclination	2.240951°
Longitude of ascending node	304.34152°
Time of perihelion	≈ 20 October 2055 ±3 months
Argument of perihelion	222.597°
Known satellites	1 at 2,777 ± 19 km (1,725 ± 10 mi)
Earth MOID	42.3938 AU (6.34202 Tm)
Jupiter MOID	37.9599 AU (5.67872 Tm)
Physical characteristics
Dimensions	≈ 250±30 km (Sila) ≈ 235±28 km (Nunam) (335+41 −42 km combined)
Mass	1.084 ± 0.022×10 kg (combined)
Mean density	0.72 −0.22 g/cm
Synodic rotation period	300.24 h (12.510 d)
Sidereal rotation period	12.50995 ± 0.00036 d
Geometric albedo	0.086 −0.017
Temperature	~42 K (−384 °F)
Spectral type	U−B=0.73 B−V=1.08 V−R=0.66±0.04 B−R=1.74 V−I=1.25±0.03 R−J=1.4 V−J=2.06±0.03 J−H=0.38±0.08 V−H=2.45±0.08
Apparent magnitude	21.54–21.78 (2014–2015)
Absolute magnitude (H)	(combined) 5.5, (individual) 6.2 & 6.3 (diff. = 0.12), 5.2

79360 Sila–Nunam (provisional designation 1997 CS₂₉) is a cold classical Kuiper belt object (cubewano) and binary system made up of components of almost equal size, called Sila and Nunam, orbiting beyond Neptune in the Solar System. The name of the system is the combined names of the two bodies, Sila and Nunam.

Discovery

Sila–Nunam was discovered on 4 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 on 5 October 2005.

Name

The two components are named after Inuit deities. Sila "air" (Iñupiaq siḷa , Inuktitut sila) is the Inuit god of the sky, weather, and life force. Nuna "earth" (Iñupiaq amn Inuktitut nuna-m ) is the Earth goddess, in some traditions Sila's wife. Nuna created the land animals and, in some traditions, the Inuit (in other traditions Sila created the first people out of wet sand). Sila breathed life into the Inuit.

Orbit

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

Physical characteristics

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 of 250 to 420 km (155 to 260 mi). 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. There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion.

Sila–Nunam experiences periodic changes in brightness with the full period, which is equal to the orbital binary period (see below). The light curve is double peaked with the secondary period equal to half of the full period. The rotation of both components of the system is synchronously locked with the orbital motion and both bodies are elongated with their long axes pointing to each other. From 2009 to 2017 Sila–Nunam experienced mutual occultation events.

Double system

Sila and Nunam are so close in size (within 5%) that they may be thought of as a double cubewano. Sila is approximately 250 km in diameter and Nunam 236 km. Their albedo is about 9%. They orbit at a distance of 2,777 ± 19 km (1,726 ± 12 mi) every 12.51 days:

Semi-major axis:	2,777 ± 19 km
Orbital period:	12.50995 ± 0.00036 d
Eccentricity:	0.020 ± 0.015°
Inclination:	103.51 ± 0.39°

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

References

1. "List of Transneptunian Objects". IAU Minor Planet Center. Archived from the original on 15 October 2008. Retrieved 2 August 2010.
2. There is no established pronunciation of these names in English, but this is perhaps the easiest way to say them. Depending on dialect and accent, the Inuit language vowels i and u may be similar to English seal and noon or to sill and nook. The a can vary in a way reminiscent of how the 'a' in English "an" does (that is, from the 'a' of sofa to the 'a' of cat). Likewise, the stressed syllable varies, as Inuit languages do not have distinctive stress. Thus a wide range of English pronunciations can approximate Eskimo–Aleut languages.
3. "MPEC 2009-R09 :Distant Minor Planets (2009 SEPT. 16.0 TT)". IAU Minor Planet Center. 4 September 2009. Retrieved 4 October 2009.
4. Marc W. Buie. "Orbit Fit and Astrometric record for 79360" (2 February 2009 using 142 observations). SwRI (Space Science Department). Retrieved 4 October 2009.
5. See Mallon (2000) Inuktitut Linguistics for Technocrats: Morphology
6. ^ "JPL Small-Body Database Browser: 79360 Sila-Nunam (1997 CS29)" (2014-01-28 last obs). Retrieved 25 March 2016.
7. JPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
8. ^ "(79360) Sila-Nunam". Wm. Robert Johnston. 11 January 2012. Archived from the original on 19 July 2012. Retrieved 12 January 2012.
9. ^ W.M. Grundy; S.D. Benecchi; D.L. Rabinowitz; et al. (2012). "Mutual events in the Cold Classical transneptunian binary system Sila and Nunam". Icarus. 220: 74–83. arXiv:1204.3923. Bibcode:2012Icar..220...74G. doi:10.1016/j.icarus.2012.04.014.
10. ^ 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.
11. ^ David L. Rabinowitz; Susan D. Benecchi; William M. Grundy; Anne J. Verbiscer (2014). "The rotational light curve of (79360) Sila–Nunam, an eclipsing binary in the Kuiper Belt". Icarus. 236: 72–82. arXiv:1404.0244. Bibcode:2014Icar..236...72R. doi:10.1016/j.icarus.2014.03.046.
12. ^ Stephen C. Tegler. "Kuiper Belt Object Magnitudes and Surface Color". Archived from the original on 1 September 2006. Retrieved 1 August 2010.
13. Sila–Nunam Mutual Events (Lowell)
14. For some reason, Nunam includes the subject/possessive suffix -m, while Sila does not. There is no such distinction in Inuit. E.g. nuna-m-i is 'on land' while sila-m-i is 'outside' ("in the air").
15. 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.
16. Fornasier, S.; Barucci, M.A.; de Bergh, C.; et 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.
17. Boehnhardt, H.; Bagnulo, S.; Muinonen, S.; et 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.
18. Rabinowitz, et al. (2009). "Evidence for Recent Resurfacing of the Binary Kuiper Belt Object 1997 CS29".

External links

• 79360 Sila–Nunam at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 79360 Sila–Nunam at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• Minor planet object articles (numbered)
• Cold classical Kuiper belt objects
• Discoveries by Chad Trujillo
• Discoveries by Jun Chen (astronomer)
• Discoveries by Jane Luu
• Discoveries by David C. Jewitt
• Named minor planets
• Binary trans-Neptunian objects
• Slow rotating minor planets
• Astronomical objects discovered in 1997
• Possible dwarf planets