79360 Sila–Nunam

79360 Sila–Nunam, provisional designation 1997 CS29, is a double cold[8] 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.[12]

Sila–Nunam
Sila–Nunam imaged by the Hubble Space Telescope in 2004
Discovery
Discovered byJ. X. Luu
D. C. Jewitt
C. A. Trujillo
J. Chen [1]
Discovery siteMauna Kea Obs.
Discovery date4 February 1997
Designations
(79360) Sila–Nunam
Pronunciation/ˈsiːlə ˈnuːnəm/[2]
1997 CS29
TNO (cubewano)[3][4]
AdjectivesSilaupian, Nunaupian[5]
Orbital characteristics[6]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc6940 days (19.00 yr)
Aphelion44.8452 AU (6.70875 Tm)
Perihelion43.3862 AU (6.49048 Tm)
44.1157 AU (6.59961 Tm)
Eccentricity0.016536
293.02 yr (107026 d)
331.884°
0.00336367°/day
Inclination2.240951°
304.34152°
222.597°
Known satellites1 at 2,777 ± 19 km (1,725 ± 10 mi)[7][8]
Earth MOID42.3938 AU (6.34202 Tm)
Jupiter MOID37.9599 AU (5.67872 Tm)
Physical characteristics
Dimensions≈ 250±30 km (Sila)
≈ 235±28 km (Nunam)
(335+41
−42 km combined)[7][8][9]
Mass1.084 ± 0.022×1019 kg (combined)[8]
Mean density
0.72+0.37
−0.22 g/cm3
300.24 h (12.510 d)
12.50995 ± 0.00036 d[10]
0.086+0.026
−0.017[7]
Temperature~42 K (−384 °F)
U−B=0.73[7]
B−V=1.08[7][11]
V−R=0.66[11]±0.04[7]
B−R=1.74[7]
V−I=1.25±0.03[7]
R−J=1.4[7]
V−J=2.06±0.03[7]
J−H=0.38±0.08[7]
V−H=2.45±0.08[7]
21.54–21.78 (2014–2015)
(combined) 5.5,[11]
(individual) 6.2 & 6.3 (diff. = 0.12),[7]
5.2[6]

    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 [siʎə], Inuktitut sila) is the Inuit god of the sky, weather, and life force. Nuna "earth" (Iñupiaq & Inuktitut nuna-m [nunəm])[13] is the Earth goddess, in some traditions Sila's wife. Nuna 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.[6]

    Orbit

    Sila–Nunam is a dynamically cold classical system (cubewano). It orbits very close to 4:7 mean-motion resonance with Neptune.[9]

    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 250 to 420 km (155 to 260 mi).[9] 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.[14][15] There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion.[16]

    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 the 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.[10] From 2009 to 2017 Sila–Nunam experienced mutual occultation events.[8]

    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:[8][10]

    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.[17]

    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 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 does not have distinctive stress. Thus a wide range of English pronunciations can approximate the Inuit.
    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. "(79360) Sila-Nunam". Wm. Robert Johnston. 11 January 2012. Archived from the original on 15 July 2012. Retrieved 12 January 2012.
    8. 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.
    9. 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.
    10. 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.
    11. Stephen C. Tegler. "Kuiper Belt Object Magnitudes and Surface Color". Archived from the original on 1 September 2006. Retrieved 1 August 2010.
    12. Sila–Nunam Mutual Events (Lowell)
    13. 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").
    14. 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.
    15. 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.
    16. 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.
    17. Rabinowitz, et al. (2009). "Evidence for Recent Resurfacing of the Binary Kuiper Belt Object 1997 CS29".
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