Astronomer Michael Brown estimates that, with an absolute magnitude of 3.5 and a calculated diameter of approximately 700–800 kilometers (430–500 miles),[14][15] it is likely a dwarf planet.[16]
However, William M. Grundyet al. argue that objects 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.[17] It is not clear if Varda has a low or a high density.
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.[18]
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.[1] As of November 2019[update], Varda is 47.5 AU from the Sun.[12] It will come to perihelion around November 2096.[6] It has been observed 321 times over 23 oppositions, with precovery images back to 1980.[1][2]
Name
The names for Varda and its moon were announced by the Minor Planets Center on 16 January 2014. Varda (Quenya:[ˈvarda]) is the queen of the Valar, creator of the stars, one of the most powerful servants of almighty Eru Ilúvatar in J. R. R. Tolkien's fictional mythology. Ilmarë is a chief of the Maiar and Varda's handmaiden.[2]
The use of planetary symbols is discouraged in astronomy, so Varda never received a symbol in the astronomical literature. There is no standard symbol for Varda used by astrologers either. Zane Stein proposed a gleaming star as the symbol ().[19]
Varda has one known 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 are the same as that of Varda.[b]
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.[8] The total mass of the binary system is approximately 2.66×1020kg. The density of both the primary and the satellite is estimated at 1.24 g/cm3, assuming that they have equal density.[10][8] 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.[8]
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.[7] Given Varda's equivalent diameter derived from the occultation, its geometric albedo is measured at 0.099, making it as dark as the large plutino2003 AZ84.
The rotation period of Varda is unknown; it has been estimated at 5.61 hours in 2015,[8] and more recently (in 2020) as either 4.76, 5.91 (the most likely value), 7.87 hours, or twice those values.[7] The large uncertainty in Varda's rotation period yields various solutions for its density and true oblateness; given a most likely 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.[7]
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.[citation needed]
See also
(55565) 2002 AW197 – a similar trans-Neptunian object by orbit, size, and color
Notes
^Assuming equal albedos for the primary and the secondary
^ abUsing Grundy et al.'s working diameters of 361 km and 163 km, and assuming the densities of the two bodies are equal, Varda would contribute 91.6% of the system mass of (2.664±0.064)×1020 kg.[8]
^ abJPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
^W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)', Icarus(forthcoming, available online 30 March 2019)Archived 7 April 2019 at the Wayback Machine DOI: 10.1016/j.icarus.2018.12.037,
^Larsen, Jeffrey A.; Roe, Eric A.; Albert, C. Elise; et al. (2007). "The Search for Distant Objects in the Solar System Using Spacewatch". The Astronomical Journal. 133 (4): 1247–1270. Bibcode:2007AJ....133.1247L. doi:10.1086/511155.
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