Ijiraq (moon)
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| Discovery [1] | |
|---|---|
| Discovered by | J. J. Kavelaars B. J. Gladman |
| Discovered | in 2000 |
| Mean Orbital elements [2] | |
| Epoch 2000 Feb. 26.00 | |
| Semi-major axis | 11.124 Gm |
| Eccentricity | 0.3163 |
| Inclination | 46.444° * |
| Orbital period | 451.4 d (1.24 yr) |
| Physical characteristics | |
| Mean diameter | 12 km[3] ** |
| Rotation period | ? |
| Albedo | 0.04[3] assumed |
| Color | red B-V=1.05 R-V=0.58[4] |
| Spectral type | (redder than D)[4] |
| *to the ecliptic **based on the albedo | |
Ijiraq (pronounced /ˈiːɨrɑːk/ EE-yə-raak, or /ˈiːdʒɨrɑːk/ EE-jə-raak) is a prograde irregular satellite of Saturn. It was discovered by the team of Brett Gladman, John J. Kavelaars, et al. in 2000, and given the temporary designation S/2000 S 6.[5][6] It was named in 2003 after the Ijiraq, a creature of Inuit mythology[7].
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[edit] Orbit
Ijiraq orbits Saturn at an average distance of 11.1 Gm in 451 days on an orbit very similar to Kiviuq's. The diagram illustrates its orbit in relation to other prograde irregular satellites of Saturn. The eccentricity of the orbits is represented by the yellow segments extending from the pericentre to the apocentre.
Ijiraq is believed to be in Kozai resonance i.e. its orbit is cyclically reducing the inclination while increasing the eccentricity and vice versa. The orbit’s argument of pericenter oscillates around 90° with an amplitude of 60°.[8]
[edit] Physical characteristics
While Ijiraq is a member of the Inuit group of irregular satellites,[9] recent observations revealed that Ijiraq is distinctively redder than Paaliaq, Siarnaq and Kiviuq. Its spectral slope (a measure of body reflectance in function of the wavelength) is twice as steep as for other members (20% per 100 nm), typical for red Trans-Neptunian Objects like Sedna but unknown for irregular satellites. In addition, unlike the other three, Ijiraq's spectrum lacks the weak absorption near 0.7 μm, attributed to a possible water hydration.[4]
[edit] Name
Kavelaars, an astronomer at McMaster University, suggested this name to help astronomical nomenclature to get out of its Greco-Romano-Renaissance rut. He spent several months trying to find names that were both multi-cultural and Canadian, consulting Amerindian scholars without finding a name that seemed appropriate. In March 2001, he was reading an Inuit tale to his children and had a revelation. The ijiraq plays at hide-and-seek, which is what these small moons of Saturn do: they are hard to find, and cold like the Canadian arctic (the team of discoverers includes Canadians, Norwegians and Icelanders—Nordicity is their common trait). Kavelaars contacted the author of the tale, Michael Kusugak, to get his assent, and the latter also suggested the names for Kiviuq and 90377 Sedna.
[edit] References
- ^ Discovery Circumstances (JPL)
- ^ Mean orbital parameters from JPL
- ^ a b Scott Sheppard pages
- ^ a b c Grav, T.; and Bauer, J.; A deeper look at the colors of Saturnian irregular satellites
- ^ IAUC 7521: S/2000 S 5, S/2000 S 6 2000 November 18 (discovery)
- ^ MPEC 2000-Y14: S/2000 S 3, S/2000 S 4, S/2000 S 5, S/2000 S 6, S/2000 S 10 2000 December 19 (discovery and ephemeris)
- ^ IAUC 8177: Satellites of Jupiter, Saturn, Uranus 2003 August 8 (naming the moon)
- ^ Nesvorný, D.; Alvarellos, Jose L. A.; Dones, L.; and Levison, H. F.; Orbital and Collisional Evolution of the Irregular Satellites, The Astronomical Journal, 126 (2003), pp. 398–429
- ^ Gladman, B. J.; Nicholson, P. D.; Burns, J. A.; Kavelaars, J. J.; Marsden, B. G.; Holman, M. J.; Grav, T.; Hergenrother, C. W.; Petit, J.-M.; Jacobson, R. A.; and Gray, W. J.; Discovery of 12 satellites of Saturn exhibiting orbital clustering, Nature, 412 (2001 July 12), pp. 163–166
- Ephemeris from IAU-MPC NSES
[edit] External links
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