Ilmarë
Moon of 174567 Varda
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Ilmarë,[b] formal designation (174567) Varda I, is the only known moon of the large Kuiper belt object 174567 Varda. It was discovered by Keith Noll et al. in 2009, at a separation of about 0.12 arcsec, using discovery images taken by the Hubble Space Telescope on 26 April 2009, and reported in 2011.[5] At approximately 403 km in diameter (about 45% that of its primary), it is the fourth-largest known moon of a trans-Neptunian object, after Pluto I Charon, Eris I Dysnomia, and Orcus I Vanth. Assuming that Ilmarë has the same albedo and density as Varda, Ilmarë would constitute approximately 8.4% of the system's mass, approximately 2.2×1019 kg.
Hubble Space Telescope image of Varda and its satellite Ilmarë, taken in 2010 and 2011 | |
| Discovery | |
|---|---|
| Discovered by | Keith S. Noll et al. |
| Discovery date | 2009, based on images taken on 26 April 2009 |
| Designations | |
Designation | Varda I |
| Pronunciation | /ˈɪlməriː/ |
Named after | Ilmarë (figure by J. R. R. Tolkien)[1] |
| (174567) Varda I | |
| Adjectives | Ilmarëan /ɪlməˈriːən/ |
| Orbital characteristics[2] | |
| 4805±35 km or 4812±35 km[2] | |
| Eccentricity | 0.0181±0.0045 or 0.0247±0.0048 (0.0215±0.0080 adopted) |
| 5.75058±0.00015 d | |
| Inclination | 101.0±1.9 or 85.1±1.8 |
| Satellite of | Varda |
| Physical characteristics | |
| 403±40 km[3] | |
| Mass | ≈2.2×1019 kg[2] |
Mean density | 1.24+0.50 −0.35 g/cm3 (system)[2][a] |
| Albedo | 0.068±0.011 (2025)[3] ≈0.085 (2020)[4] |
Spectral type | B−V = 0.857±0.061 V−I = 1.266±0.052[2] |
| Varda + 1.7[2] | |
Name
Names for Varda and its moon were announced on 16 January 2014. Ilmarë (Quenya: [ˈilmarɛ]) is a chief of the Maiar and handmaiden to Varda, the queen of the Valar, creator of the stars, and principal goddess of the elves in J. R. R. Tolkien's fictional mythology.[1]
Physical characteristics
Ilmarë and Varda are tightly bound, with a separation of about 13 Varda radii, and a consequently low angular momentum. Along with the high inclination of Varda's orbit, they are similar in this way to the Orcus–Vanth and Salacia–Actaea systems. As of 2015 two mirror orbital solutions are possible with slightly different orbital parameters. The calculated eccentricity is inconsistent with the likely age of the system, suggesting that it might be spurious, but the expected age is also contradicted by suggestions that Varda may not be tidally locked.[2]
If Ilmarë and Varda have the same albedo, Ilmarë would be 163+19
−17 km in radius, or approximately 8.4% the volume of Varda. If the two bodies also have the same density, Ilmarë would then have approximately 8.4% the system mass of (2.664±0.064)×1020 kg.
If, however, the albedo of Varda is 50% greater than that of Ilmarë, Ilmarë would have a radius of 191+22
−21 km and the bulk density of the system would be 1.31+0.52
−0.36 g/cm3. If Ilmarë has a 50%-greater albedo, then its radius would be 137+16
−15 km and the bulk density would be 1.18+0.47
−0.33 g/cm3. Because the absolute magnitudes of the two bodies at different wavelengths are similar, it's not likely that their albedos differ by much, so Ilmarë is likely to be in this size range.[2]
See also
- Actaea – a moon of another large trans-Neptunian object, 120347 Salacia, that is similar in size to Ilmarë