Ilmarë

Not to be confused with 2107 Ilmari.
Ilmarë
Hubble Space Telescope image of Varda and its satellite Ilmarë, taken in 2010 and 2011
Discovery
Discovered byKeith S. Noll et al.
Discovery date2009, 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
AdjectivesIlmarëan /ɪlməˈriːən/
Orbital characteristics[2]
4805±35 km or 4812±35 km[2]
Eccentricity0.0181±0.0045 or 0.0247±0.0048
(0.0215±0.0080 adopted)
5.75058±0.00015 d
Inclination101.0±1.9 or 85.1±1.8
Satellite ofVarda
Physical characteristics
Mean diameter
403±40 km[3]
Mass≈2.2×1019 kg[2] (2015)
~16% of Varda (2025)[3][a]
~11% of Varda (2025)[3][b]
Mean density
1.24+0.50
−0.35 g/cm3 (system)[2][c]
Albedo0.068±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]

Ilmarë,[d] 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, it is the fourth-largest known moon of a trans-Neptunian object, after Pluto I Charon,[6] Eris I Dysnomia,[7] and Orcus I Vanth.[8] Under the assumption of a lower density of 0.7 g/cm3, which is thought to be more typical that of trans-Neptunian objects in the ~400 km size range, the satellite-to-primary mass ratio would be approximately 0.11:1.[3]

History

Discovery

  • The Hubble Space Telescope, which discovered Ilmarë on 26 April 2009.
    The Hubble Space Telescope, which discovered Ilmarë on 26 April 2009.

Ilmarë 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]

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]

Orbit

Orbital characteristics

Ilmarë orbits Varda at a distance of 4805±35 km or 4812±35 km[2] and an eccentricity of 0.0181±0.0045 or 0.0247±0.0048 respectively.[2] Ilmarë has an orbital period of approximately 5.75058±0.00015 d.[2] Ilmarë's orbit has an inclination of 101.0±1.9° or 85.1±1.8° with respect to the ecliptic.[2]

Tidal locking

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]

Physical characteristics

  • Comparison of sizes, albedos, and colors of various large trans-Neptunian objects with diameters greater than 700 km (430 mi). Its parent body Varda is shown on the bottom row, first from the left, and ilmarë is located next to it. The dark colored arcs represent uncertainties of the object's size.
    Comparison of sizes, albedos, and colors of various large trans-Neptunian objects with diameters greater than 700 km (430 mi). Its parent body Varda is shown on the bottom row, first from the left, and ilmarë is located next to it. The dark colored arcs represent uncertainties of the object's size.

Old estimates of Ilmarë's physical properties

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 is not likely that their albedos differ by much, so Ilmarë is likely to be in this size range.[2]

More accurate measurements in 2025

Size and albedo

However, more accurate measurements in 2025 that was done by Kiss et al., measured a low albedo of 0.068±0.011 for Ilmarë,[3] which is a bit lower than the albedo of Varda (0.099±0.002),[4] yielding a larger diameter of 403±40 km km, which is about half that of its primary.[3]

Assuming that the following size estimates are correct, Ilmarë is about the fourth-biggest known moon of a trans-Neptunian object, after Charon (1212±1 km),[6] Dysnomia (615+60
−50 km),[7]: 7  and Vanth (442.5±10.2 km).[8]

Mass and density

Assuming equal densities (1.15 g/cm3) for both bodies, the resulting satellite-to-primary mass ratio is 0.16:1,[3] closely matching that of the Orcus–Vanth system.[3] Even under the assumption of a lower density of 0.7 g/cm3, which is thought to be more typical that of trans-Neptunian objects in the ~400 km size range,[3] the mass ratio remains high at 0.11:1.[3] This places Varda–Ilmarë among the systems with the largest known mass ratios, comparable to that of Pluto–Charon.[3]

Surface and spectrum

The surface of Ilmare's color is dark and moderately reddish,[3][2] with a low geometric albedo of 0.068±0.011,[3] which is a bit lower than that of Varda, and has a measured B−V color index of 0.857±0.061 and a V−I color index of 1.266±0.052,[2] which is considered a moderately red color.[2]

See also

  • Actaea – a moon of another large trans-Neptunian object, 120347 Salacia, that is similar in size to Ilmarë
  • Hiʻiaka, a similarly sized moon orbiting the dwarf planet Haumea

Notes

  1. ^ Assuming equal densities as Varda.
  2. ^ Under the assumption of a lower density of 0.7 g/cm3, which is thought to be more typical that of trans-Neptunian objects in the ~400 km size range like Ilmarë.
  3. ^ If Varda and Ilmarë have equal albedos and equal densities
  4. ^ Stressed on the first syllable

References

  1. ^ a b "174567 Varda (2003 MW12)". Minor Planet Center. Retrieved 5 June 2018.
  2. ^ a b c d e f g h i j k l m n o Grundy, W. M.; Porter, S. B.; Benecchi, S. D.; Roe, H. G.; Noll, K. S.; Trujillo, C. A.; Thirouin, A.; Stansberry, J. A.; Barker, E.; Levison, H. F. (1 September 2015). "The mutual orbit, mass, and density of the large transneptunian binary system Varda and Ilmarë". Icarus. 257: 130–138. arXiv:1505.00510. Bibcode:2015Icar..257..130G. doi:10.1016/j.icarus.2015.04.036. S2CID 44546400.
  3. ^ a b c d e f g h i j k l m n Kiss, Csaba; Gabányi, Krisztina; Moór, Attila; Müller, Thomas; Fernandez-Valenzuela, Estela; Moullet, Arielle; Borkovits, Tamás; Kalup, Csilla (9 July 2025). ALMA submm measurements of the trans-Neptunian binary system satellites Ilmarë, Actaea, Hi’iaka and Namaka (Report). Copernicus Meetings. This article incorporates text from this source, which is available under the CC BY 4.0 license.
  4. ^ a b Souami, D.; Braga-Ribas, F.; Sicardy, B.; Morgado, B.; Ortiz, J. L.; Desmars, J.; et al. (August 2020). "A multi-chord stellar occultation by the large trans-Neptunian object (174567) Varda". Astronomy & Astrophysics. 643: A125. arXiv:2008.04818. Bibcode:2020A&A...643A.125S. doi:10.1051/0004-6361/202038526. S2CID 221095753.
  5. ^ a b Vilenius, E.; Kiss, C.; Mommert, M.; Müller, T.; Santos-Sanz, P.; Pal, A.; Stansberry, J.; Mueller, M.; Peixinho, N.; Fornasier, S.; Lellouch, E.; Delsanti, A.; Thirouin, A.; Ortiz, J. L.; Duffard, R.; Perna, D.; Szalai, N.; Protopapa, S.; Henry, F.; Hestroffer, D.; Rengel, M.; Dotto, E.; Hartogh, P. (4 May 2012). "'TNOs are Cool': A survey of the trans-Neptunian region". Astronomy & Astrophysics. 541: A94. arXiv:1204.0697. Bibcode:2012A&A...541A..94V. doi:10.1051/0004-6361/201118743. S2CID 54222700.
  6. ^ a b Stern, S.A.; Bagenal, F.; Ennico, K.; Gladstone, G.R.; Grundy, W.M.; McKinnon, W.B.; Moore, J.M.; Olkin, C.B.; Spencer, J.R. (16 October 2015). "The Pluto system: Initial results from its exploration by New Horizons". Science. 350 (6258) aad1815. arXiv:1510.07704. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913. S2CID 1220226.
  7. ^ a b Brown, Michael E.; Butler, Bryan J. (1 October 2023). "Masses and Densities of Dwarf Planet Satellites Measured with ALMA". The Planetary Science Journal. 4 (10): 193. arXiv:2307.04848. Bibcode:2023PSJ.....4..193B. doi:10.3847/PSJ/ace52a.
  8. ^ a b Sickafoose, A. A.; Bosh, A. S.; Levine, S. E.; Zuluaga, C. A.; Genade, A.; Schindler, K.; Lister, T. A.; Person, M. J. (1 February 2019). "A stellar occultation by Vanth, a satellite of (90482) Orcus". Icarus. 319: 657–668. arXiv:1810.08977. Bibcode:2019Icar..319..657S. doi:10.1016/j.icarus.2018.10.016. S2CID 119099266.
This article is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.