Planetoidal Class
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There are minor planets in every solar system, bodies that represent the embryos of growing planets in a young solar system, and the still born remains of planets in old systems. Yet, despite their small size, these worlds are capable of possessing unique characteristics in nearly every facet that the larger, Terrestrial planets have. Most have barren, cratered surfaces, but many possess surface deposits of ice, and some even have tenuous atmospheres.
By definition, Planetoidal Class bodies range from 51 kilometers to 1,000 kilometers in diameter. These small worlds also tend to be more spherical in shape, reflecting their larger sizes and greater gravity.
In most cases, Planetoidal bodies initially begin to form in independent orbits, and seem to be well on the way to forming a true planet. However, various circumstances can arrest this development, and either leave the Planetoid alone in a planetary orbit, or surrounded by other Planetoids and asteroids, as in a belt. In the Sol System, for example, the Asteroid Belt contains many Planetoids, the largest of which is Ceres. Quite possibly Ceres, or its large cousin Vesta, are the remnants of a failed planet. Other Planetoids can form in the furthest reaches of a solar system, and make up the majority of objects to be found in the local Kuiper belt. Some of these may find their way into the realm of the outer planets and remain as wanderers, or even be captured and become Jovian moons.
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Hadean Type As planets form and gain mass, they become differentiated due to both pressure and heat. What usually results is a world with a molten iron core, a mantle of somewhat lesser dense material that can be semi-molten, and a "light" crust of basaltic elements. This same differentiation occurs in Planetoids as they form. Often times, if a particular pre-solar nebula is metal rich, Planetoids will form that are composed almost entirely of heavy elements. These are rare worlds, however, even in metal rich systems, primarily due to the fact that most of the heavy elements will have been gathered up by the sun. Indeed, it is exceedingly rare that such a world will ever attain a Terrestrial classification. Hadeans may also be formed when a Planetoid with a large iron core has nearly all of its mantle and core blown off by a massive impact early in the formative history. The result is a world literally laid bare. |
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Cerean Type Commonly called rock dwarf worlds, these bodies can be among the most common types found in any solar system. Forming in the inner part of a solar system, they are essentially gigantic and geologically inert silicate conglomerations. While some strata differentiation may have occurred during the world's early formative period, further geological development is almost always entirely driven by outside influences, such as impact events or gravitational heating due to close encounters with much larger bodies. However, in a mature solar system these worlds will have either formed as moons, or will have been relegated to stable orbits in asteroid belts or even in single solar orbits. Cerean worlds may have varying amounts of heavy metals, of course, depending on the initial metallicity of the parent sun. The cores of the body tend to have the highest concentrations of heavy metals, while lighter materials, including volatiles, are found in the upper crustal regions. Indeed, water ice may be accumulated on permanently shadowed regions of the surface over the body's lifetime. |
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Vestian Type While planetesimals may typically be low-massed and geologically inert, there is a rare Type that exhibits ancient and extensive geological activity. Named the Vestian Type, in honor of the first known Planetoid of this division, the surfaces of these worlds are marked by ancient lava flows and even maria, and the crusts are composed largely of olivine and other such minerals. Theories for how such small worlds could exhibit evidence of ancient volcanism and differentiation abound, ranging from gravitational and tidal stressing in the past to these worlds actually being the remains of a Terrestrial world, catastrophically disrupted in some natural or even artificial disaster. Whatever the case, these worlds remain rare, indicating that the processes which do lead to their formation are themselves rare and unknown. |
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Kuiperian Type Kuiperian worlds are those that have formed in the extreme outer regions of a solar system, where the materials are so rare that they never had a change to grow very large. They are also considered to be representative of the proto-planetary disk, largely unchanged since their initial formation. As such, scientifically, they are of great interest. They are also excellent sources for volatiles, being composed primarily of water and other ices. For the most part, these bodies are confined to a specific region, called the Kuiper belt, typically ranging out to and beyond 40 AU from the parent sun. As such, these regions are highly vulnerable to gravitational influences of stellar close encounters. Occasionally, two suns will pass close enough to allow for the swapping of Kuiper objects. Such transferred worlds are found in highly eccentric orbits, making them potential objects for further gravitational disturbing by the other bodies of that solar system. Indeed, in a system where there are such orbital oddities, once every ten thousand years sees the approach of a Kuiper object to the inner solar system, forming a truly massive and tremendously bright comet. |
