| Minorplanet: | yes |
| Background: |
|
| 79360 Sila–Nunam | |
| Pronounced: | [1] |
| Adjectives: | Silaupian, Nunaupian[2] |
| Discoverer: | J. X. Luu D. C. Jewitt C. A. Trujillo J. Chen [3] |
| Discovered: | 4 February 1997 |
| Mpc Name: | (79360) Sila–Nunam |
| Mp Category: | TNO (cubewano)[4] [5] |
| Orbit Ref: | [6] |
| Epoch: | 13 January 2016 (JD 2457400.5) |
| Semimajor: | 44.1157AU |
| Perihelion: | 43.3862AU |
| Time Periastron: | ≈ 20 October 2055[7] ±3 months |
| Aphelion: | 44.8452abbr=onNaNabbr=on |
| Eccentricity: | 0.016536 |
| Period: | 293.02 yr (107026 d) |
| Inclination: | 2.240951° |
| Asc Node: | 304.34152° |
| Arg Peri: | 222.597° |
| Satellites: | 1 at NaN2,777[8] |
| Dimensions: | ≈ (Sila) ≈ (Nunam) (combined) |
| Mass: | 1.084 ± 0.022 kg (combined) |
| Density: | 0.72 g/cm3 |
| Sidereal Day: | 12.50995 ± 0.00036 d |
| Abs Magnitude: | (combined) 5.5,[9] (individual) 6.2 & 6.3 (diff. = 0.12), 5.2 |
| Albedo: | 0.086 |
| 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 |
| Single Temperature: | ~NaN42 |
| Magnitude: | 21.54–21.78 (2014–2015) |
| Rotation: | 300.24abbr=onNaNabbr=on |
| Observation Arc: | 6940 days (19.00 yr) |
| Uncertainty: | 3 |
| Moid: | 42.3938AU |
| Jupiter Moid: | 37.9599AU |
| Mean Motion: | 0.00336367°/day |
79360 Sila–Nunam (provisional designation ) 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.[10]
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 . 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.
The two components are named after Inuit deities. Sila "air" (Iñupiaq siḷa pronounced as /[siʎə]/, Inuktitut sila) is the Inuit god of the sky, weather, and life force. Nuna "earth" (Iñupiaq amn Inuktitut nuna-m pronounced as /[nunəm]/)[11] 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.[6]
Sila–Nunam is a dynamically cold classical system (cubewano). It orbits very close to 4:7 mean-motion resonance with Neptune.
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 250to.[12] Now that it is known to be a binary system, one body 95% the size of the other, the diameters are estimated to be 243and.
Sila–Nunam is very red in visible light and has a flat featureless spectrum in the near-infrared.[13] [14] There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion.[15]
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.[16]
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 NaN2,777 every 12.51 days:[16] [17]
| 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.[18]