The Kuiper belt is a vast region of billions of solid, icy planetesimals, or cometary nuclei, lying in the far outer regions of the solar system. This belt is believed to extend from the orbit of Neptune (about 30 astronomical units [AU]) out to a distance of 1,000 AU from the Sun. The existence of this region was first suggested
in 1951 by the Dutch-American astronomer, Gerard P. Kuiper (1905–73), for whom it is now named. The first Kuiper belt object, called 1992 QB, was discovered in 1992. This icy planetesimal
has a diameter of approximately 125 miles (200 km), an orbital period of some 296 years, and an average distance from the Sun of about 44 astronomical units. 1992 QB is about the size
of a major asteroid, with the suspected icy composition of a cometary nucleus. It is, therefore, similar to an interesting group of icy bodies called the Centaurs that are found in the outer
solar system between the orbits of Neptune and Saturn. Quaoar is a large object in the Kuiper belt that was first observed in June 2002. Quaoar is an icy world with a diameter of about 775
miles (1,250 km)—making it about half the size of Pluto. Located some 1 billion miles (1.6 billion km) beyond Pluto and about 4 billion miles (6.4 billion km) away from Earth, Quaoar takes 285
years to go around the Sun. The icy planetesimal travels in a nearly circular orbit around the Sun. The name Quaoar (pronounced kwah-o-wahr) comes from the creation mythology of the
Tongva—a Native American people who inhabited the Los Angeles, California, area before the arrival of European explorers and settlers. Like the planet Pluto, Quaoar dwells in
the Kuiper belt—an icy debris field of cometlike bodies extending 5 billion miles (8 billion km) beyond the orbit of Neptune. While astronomers generally treat Pluto as both a
planet and a member of the Kuiper belt, they regard Quaoar, however, as simply a Kuiper belt object (KBO). In addition, despite its size, astronomers do not consider Quaoar to be the
long-sought, hypothesized tenth planet. Nevertheless, it remains an intriguing and impressive new world, most likely consisting of equal portions of rock and various ices, including water
ice, methane ice (frozen natural gas), methanol ice (alcohol ice), carbon-dioxide ice (dry ice), and carbon-monoxide ice. Measurements made at the Keck Telescope indicate the presence of
water ice on Quaoar. The Kuiper belt is thought to be the source of the short-period comets that visit the inner solar system. Scientists now believe that the icy
objects found in this region are remnants of the primordial materials from which the solar system formed.