Quaoar is the name of a Kuiper Belt object which orbits the Sun at a mean distance of 43.6 times the Earth-Sun distance. At that orbital distance, Quaoar takes 288 Earth years to go around the Sun once. Travelling at a speed of 20 kilometres per second, it will take roughly a decade to travel from the Earth to Quaoar. Additionally, Quaoar also has a moon named Weywot which orbits it with period of close to twelve and a half days. Weywot orbits Quaoar at a mean orbital distance of approximately 14500 kilometres from Quaoar.
A paper by W. C. Fraser and M. E. Brown (2010) entitled “Quaoar: a Rock in the Kuiper Belt” describes the unique properties of the Quaoar-Weywot system and some new observations of this fascinating far-flung system. Quaoar is about 900 kilometres in diameter and in comparison; Pluto has a diameter of 2300 kilometres. The orbit of Weywot around Quaoar reveals that Quaoar has a mass that is approximately 12 percent of Pluto’s. This gives Quaoar an estimated mean density of 4.2 grams per cubic centimetre which makes Quaoar one of the densest known objects in the Kuiper Belt. Additionally, Quaoar’s moon Weywot is estimated to have a diameter of 74 kilometres. A human being with a weight of 70 kilograms on the Earth’s surface will weigh less than 4 kilograms on the surface of Quaoar!
Quaoar’s unusually high density implies that it contains proportionally less icy materials than other Kuiper Belt objects and its high density is also reminiscent of objects in the main asteroid belt which are located much closer to the Sun than Quaoar. Therefore, a substantial bulk of Quaoar is probably made up of much denser rocky material instead of the less dense icy materials.
One theory which explains Quaoar’s unusually high density states that Quaoar collided with another object which stripped away most of Quaoar’s less dense icy mantle and left behind the denser rocky core. This collision event increased the mean density of Quaoar to the current observed value as a larger proportion of Quaoar’s mass is now comprised of denser rocky material.
Another theory which might explain Quaoar unusually high density states that Quaoar formed much closer to the Sun in the main asteroid belt where objects formed there typically have densities similar to the current density observed for Quaoar. Subsequently, gravitational interaction with the planets scattered Quaoar further from the Sun and into the frigid realm of the distant Kuiper Belt objects where Quaoar has been residing ever since.
Regarding the exploration of objects in the Kuiper Belt, NASA’s New Horizons spacecraft is currently on its way to Pluto and it is scheduled to make closest approach to Pluto on 14 July 2015. This will be the first ever flyby of a Kuiper Belt object. In fact on 17 October 2010, New Horizons would have travelled half the flight time to reach Pluto since its launch on 19 January 2006. After making its flyby of Pluto and its moons, Charon, Nix and Hydra, New Horizons is also scheduled to flyby one or more Kuiper Belt objects. Visit http://pluto.jhuapl.edu/ to obtain all the latest news about this mission.