Kuiper Belt Objects (KBOs)
Kuiper Belt Objects (KBOs) refer to a group of small, ice and rock celestial bodies located in the Kuiper Belt, a region of the solar system beyond Neptune. Estimated to be formed around 4.6 billion years ago during the solar system's formation, KBOs are believed to contain primitive materials that have remained relatively unchanged over time. The Kuiper Belt is named after astronomers Kenneth Edgeworth and Gerard Kuiper, who first proposed its existence. The classification of KBOs includes three main types based on their orbital characteristics: classical (further divided into "cold" and "hot"), resonance, and scattered KBOs. Cold classical KBOs have stable, circular orbits, while hot classical KBOs exhibit more eccentric orbits. Resonance KBOs, like Pluto, maintain specific orbital relationships with Neptune. Scattered KBOs possess highly eccentric orbits that can take them far from the Kuiper Belt. The study of these objects is crucial for understanding the early solar system, and space missions such as NASA's New Horizons have significantly advanced our knowledge of KBOs and their characteristics.
Kuiper Belt Objects (KBOs)
FIELDS OF STUDY: Astrophysics; Observational Astronomy; Sub-planet Astronomy
ABSTRACT: Kuiper Belt objects (KBOs) are small icy space bodies that populate an area of the solar system known as the Kuiper Belt. This section of space is beyond the orbit of Neptune and contains more than one thousand known KBOs. They are thought to be composed of unspoiled material from the origin of the solar system. Thus, KBOs have important research potential.
Origins of Kuiper Belt Objects (KBOs)
Also known as the Edgeworth-Kuiper Belt, the Kuiper Belt is a section of the solar system occupied by small ice and rock objects called Kuiper Belt objects (KBOs). They are also known as transneptunian objects (TNOs). These small, irregularly shaped space bodies are thought to contain untouched material from the formation of the solar system 4.6 billion years ago. The Kuiper Belt is named after the men who first theorized it existed, Kenneth Edgeworth (1880–1972) and Gerard Kuiper (1905–73). In 1992, its existence was confirmed, which led to Pluto being downgraded from a planet to a dwarf planet that is also considered a KBO.
Types of KBOs
KBOs are divided into three classes based on their orbit: classical, resonance, and scattered. Classical KBOs are subdivided into "cold" and "hot" classical KBOs. Cold classical KBOs have a semi-major axis, or mean distance from the sun, of 42 to 48 astronomical units (AU), or 390 million to 446 million miles. Their orbits are not eccentric—that is, they are fairly circular. Cold classical KBOs are also low inclination. In other words, they do not orbit at an angle. They are called "cold" not because of their temperature but because of their relatively calm movement. Their smaller size and reddish appearance lead scientists to think cold classical KBOs have a different origin than other types. Hot classical KBOs have less controlled orbits. Their more eccentric orbit and higher inclination path mean they are less likely to stay the same average distance from the sun. They are generally bigger and tend to be gray in color.
Resonance KBOs orbit the sun in a consistent ratio to Neptune. Most of these are in 3:2 resonance, orbiting the sun twice for every three orbits Neptune completes. Pluto is among the 3:2 resonant KBOs. Others travel farther from the sun and are in 2:1 resonance, making only one trip around the sun for every two that Neptune makes.
Scattered KBOs are also known as scattered disk objects (SDOs). They are space bodies made of ice and rock. They have very eccentric, or flattened, oval orbits that take them both closer to and farther from the sun than the other types of KBOs. Not all SDOs are KBOs, however. Some are farther from the sun or farther above or below the ecliptic (sun’s path) than the Kuiper Belt proper.
Scientists have observed other objects with similar properties to the KBOs. However, their very eccentric orbits may keep them from being considered part of the Kuiper Belt.
The Kuiper Belt and Pluto
When astronomers David Jewitt (b. 1958) and Jane Luu (b. 1963) confirmed the existence of the first KBO, 1992QB1, in 1992, it was the beginning of the end of planet status for Pluto. Scientists had long theorized that the belt of asteroids must be there. However, the great distance between Earth and the area that came to be known as the Kuiper Belt made it difficult to see any objects there with even the strongest telescope.
Jewitt and Luu’s success led to the discovery of other KBOs. This, in turn, led scientists to realize that Pluto had more in common with those objects than with the other eight primary planets. Pluto is larger than most KBOs and relatively reflective. This makes it easier to see from Earth than other KBOs, which is why it was spotted in 1930 and designated a planet. However, with the discovery of other KBOs of similar size and orbit, the International Astronomical Union demoted Pluto to a dwarf planet in 2006. Dwarf planets orbit the sun like the primary eight planets but cannot knock other objects out of their orbits. They are smaller than the primary planets and cannot maintain any known form of life. Other dwarf planets include Eris, which is about the same size as Pluto, and Ceres, the largest known asteroid in the asteroid belt.
KBOs and the Origin of the Solar System
KBOs are valuable to scientists because they are thought to be made up of materials left over from the formation of the solar system about 4.6 billion years ago. They have likely gone unchanged for billions of years. Thus, their composition could tell scientists much about the early solar system.
The European Space Agency (ESA) spacecraft Rosetta and the National Aeronautic and Space Administration spacecraft New Horizons were launched in 2004 and 2006 respectively to explore the Kuiper Belt for that reason. Both Rosetta and New Horizons approached KBOs. Rosetta released a probe, Philae, when it rendezvoused with comet 67P/Churyumov-Gerasimenko in 2014. The probe bounced upon landing on the comet and provided relatively less data than had been hoped, but Rosetta continued on to orbit the comet as it neared the sun. The spacecraft later joined the probe when the ESA crashed it onto the comet. New Horizons flew by Pluto and its moons in 2015 and in 2019 flew past 2014 MU69, the most distant object that had been viewed up close. The mission allowed scientists to accurately measure the size of Pluto before the spacecraft flew past to further investigate KBOs. As of June 2022 New Horizons was 52.44 AU from Earth and continued to transmit data.
Principal Terms
- dwarf planet: a round celestial body that is much smaller than a planet and orbits the sun, but is unable to clear other objects from its orbit. Made of solid rock, ice, or both, dwarf planets are thought to be incapable of sustaining any known life.
- Edgeworth-Kuiper Belt: a ring of icy rock objects located beyond the orbit of Neptune; also known as the Kuiper Belt.
- scattered disk objects: small, icy planets with highly eccentric orbits at the farthest reaches of the solar system.
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