Mundilfari (moon)
Discovery images of Mundilfari (circled) taken by the CFHT in September 2000 | |
| Discovery | |
|---|---|
| Discovered by | Gladman et al. |
| Discovery date | 2000 |
| Designations | |
Designation | Saturn XXV |
| Pronunciation | Icelandic: [ˈmʏntɪlvarɪ] |
Named after | Mundilfari |
| S/2000 S 9 | |
| Orbital characteristics | |
| 18590300 km | |
| Eccentricity | 0.210 |
| −952.95 days | |
| Inclination | 168.4° |
| Satellite of | Saturn |
| Group | Norse group |
| Physical characteristics | |
| Dimensions | 11.78 × 7 × 5.86 km (modeled) |
| 7+50% −30% km | |
| 6.74±0.08 hours | |
| Albedo | 0.06 (assumed) |
Spectral type | P |
| 23.8 | |
| 14.5 | |
Mundilfari, or Saturn XXV, is a natural satellite of Saturn. It was discovered by Brett J. Gladman, et al. in 2000, and given the temporary designation S/2000 S 9. Mundilfari is about 7 kilometers in diameter, and orbits Saturn at an average distance of 18,5903 Mm in 952.95 days, an averaged eccentricity of 0.210, and at an inclination of 168.4° to the ecliptic in a retrograde sense (compared to Saturn's orbit around the Sun).
Mundilfari may have formed from debris knocked off Phoebe by large impacts at some point in the Solar System's history, but it is on an orbit sufficiently different from Phoebe that this may be difficult to reconcile. With a spectral slope of −5.0%/100 , Mundilfari is the bluest of all the moons studied by Grav and Bauer (2007), slightly more so than Phoebe (−2.5%/100 nm) and about as blue as Erriapus (+5.1%/100 nm) is red. Its rotation period is 6.74±0.08 hours, the second-fastest among all the irregular moons studied by Cassini–Huygens after Hati, and it appears to be very elongated in shape.
It was named in August 2003 from Norse mythology, where Mundilfari is the father of the goddess Sól (Sun) and the god Máni (Moon).
In 2023 announcements of 64 newly discovered irregular moons plus an additional 128 additional irregular moons in 2025 have suggested that Mundilfari is the largest remaining fragment of an entire sub-group of small retrograde irregular moons.