Named afterGerard Kuiperwho in 1951 actually doubted it still existed[1]
VisitedPluto (2015), Arrokoth (2019)by New Horizons[3]
About the image. Drawn as a ring of points around the Sun with the orbits of the four giant planets for scale. The objects are vastly enlarged and far too numerous to show; in reality the belt is mostly empty space.
Beyond Neptune lies a wide ring of icy bodies left over from the formation of the planets. It is called the Kuiper belt, and it is like the asteroid belt between Mars and Jupiter but far larger: it stretches from about 30 AU, the orbit of Neptune, out to about 50 AU, and holds far more material.
Found in 1992
For decades the existence of such a belt was only a guess. Frederick Leonard suggested in 1930 that Pluto might not be alone, and Kenneth Edgeworth proposed a belt of objects in 1943. In 1951 Gerard Kuiper discussed a similar disc, though he thought it would have been scattered long ago, and his name stuck anyway.
Then, on 30 August 1992, David Jewitt and Jane Luu, searching with a telescope on Mauna Kea, found a faint object moving slowly beyond Neptune. Catalogued as 1992 QB1 and later named Albion, it was the first Kuiper belt object found after Pluto and its moon Charon. Thousands more have been found since.
What is in it
Astronomers estimate that the belt holds more than 100 000 objects larger than 100 kilometres across, and vastly more smaller ones. Yet all together they weigh only about 2% as much as Earth. The largest member is Pluto. Others include dwarf planets and large bodies such as Haumea, Makemake, Quaoar and Orcus.
Neptune’s gravity sculpts the belt. Many objects, including Pluto and Orcus, are locked in resonances with it, orbiting twice for every three Neptune orbits. Beyond about 50 AU the number of objects drops sharply, an edge sometimes called the Kuiper cliff. Its cause is not known.
Visited twice
NASA’s New Horizons is the only spacecraft to explore the Kuiper belt. It flew past Pluto in July 2015 and the small object Arrokoth on New Year’s Day 2019, revealing a contact binary preserved since the birth of the Solar System. Beyond the belt lies the scattered disc, and much further still, the Oort cloud.
Gallery
A bright Sun surrounded by a wide, flat band of glittering golden particles curving around it, an impression of the Kuiper belt. AI-generated painting.Several reddish and grey icy bodies of different sizes scattered through dark space, the Sun only a small bright star in the distance, an impression of objects in the Kuiper belt. AI-generated painting.The Kuiper belt, 3D artist's impression, rendered from the interactive model.The Kuiper belt, 3D artist's impression, from another angle, rendered from the interactive model.The Kuiper belt, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
1943Kenneth Edgeworth proposes a belt of bodies beyond Neptune.
1951Gerard Kuiper discusses a similar disc.
1992David Jewitt and Jane Luu find 1992 QB1, the first Kuiper belt object after Pluto and Charon.
2015New Horizons flies past Pluto.
2019New Horizons flies past Arrokoth.
Questions people ask
Where is the Kuiper belt?
Beyond Neptune, from about 30 to 50 AU from the Sun.
How many objects are in the Kuiper belt?
More than 100 000 larger than 100 km are estimated, and many more smaller ones.
Is Pluto in the Kuiper belt?
Yes. It is the belt's largest known member.
What is the difference between the Kuiper belt and the Oort cloud?
The Kuiper belt is a flat ring just beyond Neptune that has been observed. The Oort cloud is a far larger, roughly spherical shell thousands of AU away, inferred from comets but never seen.