Varuna

Observations within the last decade have revealed the existence of a large number of bodies in orbit about the sun beyond Neptune. These bodies, commonly known as Kuiper Belt Objects (KBOs), are products of agglomeration in the rarefied outer regions of the protoplanetary disk of the sun. Scientific interest focuses on the primitive nature of the KBOs and on their role as the likely source of short-period comets. Unfortunately, the KBOs are difficult astronomical targets, so that even such basic physical properties as the sizes and albedos remain unknown. Here we report the first simultaneous thermal and optical measurements of a bright KBO and use them to solve separately for the albedo and size. (20000) Varuna has equivalent circular diameter D = 900(+125/-145) km and red geometric albedo p = 0.070(+0.030/-0.017). The surface is darker than Pluto, suggesting a composition largely devoid of fresh ice, but higher than the canonical albedo of 0.04 previously assumed for these bodies.

20000 Varuna ("VAR oo na") is a large classical Kuiper Belt object.

It is named after the Hindu god Varuna. It previously had the provisional designation 2000 WR₁₀₆ and has been precovered in plates dating back to 1953. Under the International Astronomical Union's 2006 draft proposal for the definition of a planet, Varuna would be labelled a dwarf planet if it were proven to be spherical.