79360 Sila–Nunam

Sila–Nunam
Discovery
Discovered by Jane X. Luu, David C. Jewitt,
Chadwick A. Trujillo, Jun Chen[1]
Discovery date 3 February 1997
Designations
MPC designation (79360) Sila–Nunam
1997 CS29
TNO (cubewano)[2][3]
Adjectives Silaupian, Nunaupian[4]
Orbital characteristics[5]
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)
44.1157 AU (6.59961 Tm)
Eccentricity 0.016536
293.02 yr (107026 d)
331.884°
0.00336367°/day
Inclination 2.240951°
304.34152°
222.597°
Known satellites 1 at 2,777 ± 19 km (1,725 ± 10 mi)[6][7]
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)[6][7][8]
Mass 1.084 ± 0.022×1019 kg (combined)[7]
Mean density
 0.72+0.37
−0.22 g/cm3
300.24 h (12.510 d)
12.50995 ± 0.00036 d[9]
0.086+0.026
−0.017[6]
Temperature ~42 K (−384 °F)
U−B=0.73[6]
B−V=1.08[6][10]
V−R=0.66[10]±0.04[6]
B−R=1.74[6]
V−I=1.25±0.03[6]
R−J=1.4[6]
V−J=2.06±0.03[6]
J−H=0.38±0.08[6]
V−H=2.45±0.08[6]
21.54–21.78 (2014–2015)
(combined) 5.5,[10]
(individual) 6.2 & 6.3 (diff. = 0.12),[6]
5.2[5]

    79360 Sila–Nunam is a double cold[7] 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.[11]

    Discovery and name

    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]

    Orbit

    Sila–Nunam is a dynamically cold classical system (cubewano). It orbits very close to 4:7 mean-motion resonance with Neptune.[8]

    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).[8] 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.[12][13] There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion.[14]

    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.[9] From 2009 to 2017 Sila–Nunam will experience mutual occultation events.[7]

    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:[7][9]

    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.[15]

    References

    1. ↑ "List Of Transneptunian Objects". IAU Minor Planet Center. Archived from the original on 15 October 2008. 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. "Orbit Fit and Astrometric record for 79360" (2 February 2009 using 142 observations). SwRI (Space Science Department). Retrieved 4 October 2009.
    4. ↑ See
    5. 1 2 3 "JPL Small-Body Database Browser: 79360 Sila-Nunam (1997 CS29)" (2014-01-28 last obs). Retrieved 25 March 2016.
    6. 1 2 3 4 5 6 7 8 9 10 11 12 13 "(79360) Sila-Nunam". Wm. Robert Johnston. 11 January 2012. Retrieved 12 January 2012.
    7. 1 2 3 4 5 6 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. Bibcode:2012Icar..220...74G. arXiv:1204.3923 Freely accessible. doi:10.1016/j.icarus.2012.04.014.
    8. 1 2 3 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. Bibcode:2010A&A...518L.146M. arXiv:1005.2923 Freely accessible. doi:10.1051/0004-6361/201014683.
    9. 1 2 3 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. Bibcode:2014Icar..236...72R. arXiv:1404.0244 Freely accessible. doi:10.1016/j.icarus.2014.03.046.
    10. 1 2 3 Stephen C. Tegler. "Kuiper Belt Object Magnitudes and Surface Color". Retrieved 1 August 2010.
    11. ↑ Sila – Nunam Mutual Events (Lowell)
    12. ↑ 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.
    13. ↑ 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. Bibcode:2009A&A...508..457F. arXiv:0910.0450 Freely accessible. doi:10.1051/0004-6361/200912582.
    14. ↑ 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.
    15. ↑ Rabinowitz, et al. (2009). "Evidence for Recent Resurfacing of the Binary Kuiper Belt Object 1997 CS29".
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