20000 Varuna was discovered by the Spacewatch program at Kitt Peak on 28 November 2000.
It was given the provisional designation 2000 WR106 and has been precovered in plates dating
back to 1954.
Varuna is named after a Hindu deity that presided over the waters of the heaven and of the
ocean and was the guardian of immortality. Due to his association with the waters and the
ocean, he is often identified with Greek Poseidon and Roman Neptune. Varuna received the
minor planet number 20000 because it was the largest cubewano found so far and was believed
to be as large as Ceres.
Varuna is classified as a classical trans-Neptunian object and follows a near-circular orbit with a
semi-major axis of ≈43 AU, similar to that of Quaoar but more inclined. Its orbital period is
similar to Quaoar at 283 years. The orbits of Varuna and Pluto have similar inclination and are
similarly oriented (the nodes of both orbits are quite close). At 43 AU and on a near-circular
orbit, unlike Pluto, which is in 2:3 orbital resonance with Neptune, Varuna is free from any
significant perturbation from Neptune.
Varuna has a rotational period of approximately 6.34 hours with a double-peaked light curve.
Given the rapid rotation, rare for objects so large, Varuna is thought to be an elongated spheroid
(ratio of axis 2:3), with a mean density around 1 g/cm3 (roughly the density of water).
Examination of Varuna's light curve has found that the best-fit model for Varuna is a triaxial
ellipsoid with the axes a,b,c in ratios in the range of b/a = 0.63–0.80, and c/a = 0.45–0.52 and
a bulk density of 0.992+0.086
Since the discovery of Varuna, Haumea, another, even larger, rapidly rotating (3.9 h) object,
has been discovered and is also thought to have an elongated shape. The surface of Varuna is
moderately red (similar to Quaoar) and small amounts of water ice have been detected on its
surface. After studying the spectra corresponding to different rotational phases, there is no
indication of surface variability and the most probable composition for the surface of Varuna is a
mixture of amorphous silicates (25%), complex organics (35%), amorphous carbon (15%) and
water ice (25%). However, another possible surface composition contains up to a 10% of
methane ice. For an object with the characteristics of Varuna, this volatile could not be
primordial, so an event, such as an energetic impact, would be needed to explain its presence
on the surface.
This image comprises 3 x Luminance (200 seconds each) , 0.5m f/2.9 ASA Astrograph with FLI
ML3200 camera at an altitude of 75 degrees on 27 January 2017, 8 days after opposition at
The field of view is 18’ x 18’.
Hills Observatory: 1 January 2013 to 6 May 2018