The Kuiper belt is named after an astronomer who thought it had vanished
Gerard Kuiper did sketch a disc of icy bodies beyond Neptune, but he assumed Pluto was massive enough to have flung them all away. Had he been right, no belt would exist today. It took until 1992, after a five-year hunt, for David Jewitt and Jane Luu to find the first member beyond Pluto and Charon.
The belt stretches from Neptune's orbit, about 30 astronomical units from the Sun, out to roughly 50. It resembles the asteroid belt but is some 20 times as wide and 20 to 200 times as massive, and its objects are mostly frozen methane, ammonia and water rather than rock and metal. Most accepted dwarf planets live there, Pluto and Makemake among them, and Neptune's moon Triton may have been born there. More than 100,000 objects wider than 100 kilometres are thought to exist.
Who predicted it first is still disputed. Right after Pluto's discovery in 1930, Frederick Leonard wondered whether it was the first of a series of bodies beyond Neptune. In 1943 Kenneth Edgeworth argued that material out there was too thinly spread to form planets and instead made countless small bodies, some wandering inward as comets. The most direct forecast came from Julio Fernández in 1980, who calculated that supplying short-period comets from the far more distant Oort cloud would waste 600 comets for each one delivered, so a nearer belt between 35 and 50 units must exist.
Finding it was a slog. In 1987 Jewitt, puzzled by how empty the outer Solar System looked, recruited graduate student Luu, telling her that if they did not search, nobody would. Comparing photographic plates took about eight hours a pair until electronic CCD detectors arrived, capturing 90 percent of incoming light instead of 10 and letting the comparison happen on screen. On 30 August 1992 they announced 1992 QB1, later named Albion.
Thousands more followed. The discoveries helped reclassify Pluto as a dwarf planet in 2006, since it closely resembles its neighbours. Comets, it turns out, mostly come from the more chaotic scattered disc just beyond. New Horizons made the first close flybys, of Pluto in 2015 and Arrokoth in 2019.
Source: Kuiper belt
