Plot of all known Kuiper belt objects, set against the four outer planets
The Kuiper belt, the region’s first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice. It extends between 30 and 50 AU from the Sun. It is composed mainly of small Solar System bodies, but many of the largest Kuiper belt objects, such as Quaoar, Varuna may be reclassified as dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of the Earth. Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic.
The Kuiper belt can be roughly divided into the “classical” belt and the resonances. Resonances are orbits linked to that of Neptune. The first resonance actually begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 AU to 47.7 AU. Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, (15760) 1992 QB1.
Pluto and Charon
Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion. It is unclear whether Charon, Pluto’s largest moon, will continue to be classified as such or as a dwarf planet itself. Both Pluto and Charon orbit a barycenter of gravity above their surfaces, making
Pluto and its three known moons
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Pluto-Charon a binary system. Two much smaller moons, Nix and Hydra, orbit Pluto and Charon. Pluto lies in the resonant belt and has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos.
Scattered disc
Eris and its moon Dysnomia
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The scattered disc overlaps the Kuiper belt but extends much further outwards. This region is thought to be the source of short-period comets. Scattered disc objects are believed to have been ejected into erratic orbits by the gravitational influence of Neptune’s early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia as far as 150 AU from the Sun. SDOs’ orbits are also highly inclined to the ecliptic plane, and are often almost perpendicular to it.
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Eris
Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, since it is at least 5% larger than Pluto with an estimated diameter of 2400 km (1500 mi). It is the largest of the known dwarf planets. It has one moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto’s distance from the Sun) and an aphelion of 97.6 AU.
III. Answer the questions:
1. What are the main components of the Mid Solar System?
2. What are the types of the planets of the Mid Solar System?
3. How many planets of this region have satellites? Make a list of them.
4. What is the largest planet of the Solar System?
5. Why are all the planets of the Mid Solar System called gas giants?
6. What is the difference between a comet and asteroid?
7. What happens to the comet when it enters the Inner Solar System?
8. What are the orbits of the comets?
9. Are the comets subdivided into the groups? What are they?
10. What is a centaur? How does it differ from the comet?
11. Trans-Neptunian region consists of small ice and rocky objects, does not it?
12. What is the Kuiper belt?
13. Why do Pluto and Charon create their own binar system?
14. What can you tell about the scattered disc region?
15. What is Eris?
IV. Do you agree or disagree with the following statements? Prove your position.
1. Almost all objects in the Mid Solar System consist of ice and gas.
2. There are four gas giants in this region of the Solar System.
3. Neptune is the largest planet in the Mid Solar System.
4. Jupiter has four satellites.
5. Saturn is famous for its extensive ring system.
6. All the planets of the Mid Solar System have similarities.
7. Uranus is a gas giant and the closest planet to the Earth.
8. Comets are small Solar System bodies, usually only a few kilometers across, composed largely of volatile ices.
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9. Every comet has its own orbit.
10. Centaurs are comet-like bodies that orbit in the region between Jupiter and Neptune.
11. We know nothing about the Trans – Neptunian region.
12. The Kuiper belt, the region’s first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice.
13. Pluto is a gas giant and with its satellite Charon rotates around the Earth.
14. Eris is the largest objects of the scattered disks region.
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