— Ch. 1 · Hypotheses And Early Speculation —
Kuiper belt.
~9 min read · Ch. 1 of 7
Frederick C. Leonard pondered the existence of a trans-Neptunian population shortly after Clyde Tombaugh discovered Pluto in 1930. He asked whether Pluto was merely the first of many ultra-Neptunian bodies destined for future detection. That same year, astronomer Armin O. Leuschner suggested that Pluto might be one of many long-period planetary objects yet to be found. In 1943, Kenneth Edgeworth hypothesized that material beyond Neptune was too widely spaced to form planets and instead condensed into small bodies. He concluded that the outer solar system contained a vast number of comparatively small objects that occasionally wandered inward as comets. Gerard Kuiper speculated on a similar disc in 1951, describing it as remnants of original clusterings that lost members to become stray asteroids. He wrote about condensation products like water ice, ammonia, and methane forming aggregates up to 1 km or more in size. Kuiper believed these condensations accounted for comets in terms of size, number, and composition. He operated under the assumption that Pluto was far more massive than we now know it to be. This misconception led him to think Pluto had scattered these bodies out toward the Oort cloud or out of the solar system entirely. In 1962, physicist Alastair G. W. Cameron postulated the existence of a tremendous mass of small material on the outskirts of the solar system. Fred Whipple thought a comet belt might cause discrepancies in Uranus's orbit or affect known comets. Observation eventually ruled out this hypothesis. Charles Kowal discovered 2060 Chiron in 1977, an icy object with an orbit between Saturn and Uranus. By 1992, another object, 5145 Pholus, appeared in a similar orbit. Astronomers began speculating that centaurs must be frequently replenished by some outer reservoir. Julio Ángel Fernández published a paper in 1980 suggesting a comet belt beyond Neptune could serve as a source for short-period comets. His work laid the groundwork for what would later become known as the Kuiper belt.
Discovery And Confirmation
David C. Jewitt became increasingly puzzled by the apparent emptiness of the outer solar system while at MIT in 1987. He encouraged graduate student Jane Luu to help locate another object beyond Pluto's orbit because he told her if they did not find one, nobody would. They used telescopes at Kitt Peak National Observatory in Arizona and Cerro Tololo Inter-American Observatory in Chile. Initially, examining each pair of plates took about eight hours using a blink comparator. The process sped up with electronic charge-coupled devices or CCDs which retained 90% of light compared to the 10% achieved by photographs. In 1988, Jewitt moved to the Institute of Astronomy at the University of Hawaii where Luu joined him to work at the 2.24 m telescope on Mauna Kea. Field of view for CCDs increased to 1024 by 1024 pixels allowing searches to be conducted far more rapidly. After five years of searching, Jewitt and Luu announced on the 30th of August 1992 the discovery of candidate Kuiper belt object 1992 QB1. This object was later named 15760 Albion. Six months later they discovered a second object in the region called 181708 1993 FW. By 2018 over 2000 Kuiper belt objects had been discovered. Over one thousand bodies were found in a belt during the twenty years from 1992 to 2012 after finding 15760 Albion. Even in the 2010s the full extent and nature of Kuiper belt bodies remained largely unknown until spacecraft provided closer observations.