Ilmarë,Stressed on the first syllable or Varda I, full designation , is the single known

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...

of the Kuiper Belt planetoid

174567 Varda 174567 Varda (provisional designation ) is a binary trans-Neptunian planetoid of the resonant hot classical population of the Kuiper belt, located in the outermost region of the Solar System. Its moon, Ilmarë, was discovered in 2009. Micha ...

. 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 The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

on 26 April 2009, and reported in 2011. At approximately 326 km in diameter (about 45% that of its primary), it is the fourth or fifth-largest known moon of a

trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au). Typically ...

, after Pluto I Charon, Eris I Dysnomia, Orcus I Vanth and very possibly Haumea I Hiʻiaka. Assuming that Ilmarë has the same albedo and density as Varda, Ilmarë would constitute approximately 8.4% of the system's mass, approximately .

Name

Names for Varda and its moon were announced on 2014 January 16. Ilmarë () 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 John Ronald Reuel Tolkien (, ; 3 January 1892 – 2 September 1973) was an English writer and philologist. He was the author of the high fantasy works ''The Hobbit'' and ''The Lord of the Rings''. From 1925 to 1945, Tolkien was the Rawlins ...

's fictional mythology.

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. If Ilmarë and Varda have the same albedo, Ilmarë would be 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 . If, however, the albedo of Varda is 50% greater than that of Ilmarë, Ilmarë would have a radius of and the bulk density of the system would be . If Ilmarë has a 50%-greater albedo, then its radius would be and the bulk density would be . 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.

Notes

References

{{Moons of dwarf planets Trans-Neptunian satellites 174567 Varda Astronomical objects discovered in 2009 Things named after Tolkien works