174567 Varda

174567 Varda (provisional designation 2003 MW12) is a binary trans-Neptunian object 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.

Brown estimates that, with an absolute magnitude of 3.5 and a calculated diameter of approximately 700–800 kilometers (430–500 miles), it is likely a dwarf planet. However, Grundy et al. argue that objects such as Varda, in the size range of 400–1000 km, with albedos less than ≈0.2 and densities of ≈1.2 g/cm3 or less, have likely never compressed into fully solid bodies, let alone differentiated, and so are highly unlikely to be dwarf planets.

Discovery and orbit
Varda was discovered in March 2006, using imagery dated from 21 June 2003 by Jeffrey A. Larsen with the Spacewatch telescope as part of a United States Naval Academy Trident Scholar project.

It orbits the Sun at a distance of 39.5–52.7 AU once every 313.1 years (over 114,000 days; semi-major axis of 46.1 AU). Its orbit has an eccentricity of 0.14 and an inclination of 21.5° with respect to the ecliptic. As of November 2019, Varda is 47.5 AU from the Sun. It will come to perihelion around November 2096. It has been observed 321 times over 23 oppositions, with precovery images back to 1980.

Name
Names for Varda and its moon were announced on 16 January 2014. Varda ( Quenya: [ˈvarda]) is the queen of the Valar, creator of the stars, one of most powerful servants of almighty Eru Iluvatar in J. R. R. Tolkien's fictional mythology. Ilmarë is a chief of the Maiar and Varda's handmaiden.

Satellite
Varda has at least one satellite, Ilmarë (or Varda I), which was discovered in 2009. It is estimated to be about 350 km in diameter (about 50% that of its primary), constituting 8% of the system mass, or 2×1019 kg, assuming its density and albedo the same as that of Varda.

The Varda–Ilmarë system is tightly bound, with a semimajor axis of 4809±39 km (about 12 Varda radii) and an orbital period of 5.75 days.

Physical properties
Based on its apparent brightness and assumed albedo, the estimated combined size of the Varda–Ilmarë system is 792+91

−84 km, with the size of the primary estimated at 722+82

−76 km. The total mass of the binary system is approximately 2.66×1020 kg. The density of both the primary and the satellite is estimated at about 1.24 g/cm3 assuming that they have equal density. On the other hand, if the density or albedo of the satellite is lower than that of primary then the density of Varda will be higher up to 1.31 g/cm3.

On 10 September 2018, Varda's projected diameter was measured to be 766±6 km via a stellar occultation, with a projected oblateness of 0.066±0.047. The equivalent diameter is 740 km, consistent with previous measurements. Given Varda's equivalent diameter derived from the occultation, its geometric albedo is measured at 0.099, making it as dark as the large plutino 2003 AZ84. The large uncertainty in Varda's rotation period yields various solutions for its density and true oblateness; given a rotation period of 5.91 or 11.82 hours, its bulk density and true oblateness could be either 1.78±0.06 g/cm3 and 0.235 or 1.23 g/cm3 and 0.080, respectively.

The surfaces of both the primary and the satellite appear to be red in the visible and near-infrared parts of the spectrum (spectral class IR), with Ilmarë being slightly redder than Varda. The spectrum of the system does not show water absorption but shows evidence of methanol ice. The rotation period of Varda is estimated at 5.61 hours.