comet: The Kuiper Belt

The Kuiper Belt

In 1951, G. P. Kuiper, noting that Oort's cloud of comets did not adequately account for the population of short-period comets (those making complete orbits around the sun in less than 200 years), proposed the existence of a disk-shaped region of minor planets outside the orbit of Neptune, now called the Kuiper belt, as a source for such comets. The Kuiper belt acts as a reservoir for these in the same way that the Oort cloud acts as a reservoir for the long-period comets. This theory was validated in 1992 with the discovery of the first of more than 70,000 so-called transneptunian objects, bodies more than 60 mi (100 km) in diameter in an orbit 30–50 AU from the sun. Astronomers subsequently came to regard Pluto not as a planet but rather as dwarf planet that is a member of the Kuiper belt. The discoveries of several Kuiper belt objects led to this view. Eris, an object discovered in 2003 (and originally nicknamed Xena), has an elongated orbit that extends to roughly three times the distance of Pluto's, has a diameter (1,500 mi/2,400 km) slightly larger than that of Pluto, and has a moon; Quaoar is more than half the size of Pluto; and Ixion and Varuna are almost half the size of Pluto. 2003 VS₂ (roughly a fourth the size of Pluto) and a number of other Kuiper belt objects, called plutinos, have an orbital synchrony with Neptune like that of Pluto (Neptune completes three orbits around the sun in the same time that Pluto and the plutinos complete two orbits).

Sections in this article:

See more Encyclopedia articles on: Astronomy: General