Planet

A planet, commonly called a world, was a type of celestial body in orbit around one star or multiple. A system of planets orbiting a star could, under the correct conditions, be formed when drifting clouds of gas and dust beyond the star itself clumped together. Many scientists stated that a planet had to be large enough for its gravity to have 'cleared its orbit' by attracting all the smaller bodies in its immediate neighborhood, excluding its own satellites, known as moons. Additionally, a planet had to have a stable shape due to its gravity, becoming a regular, rounded ellipsoid, although some bodies that were known as worlds did not have a regular shape. Over time, the definition of a planet became more complicated, as scientists wanted to exclude near-stars, wandering rogue planets, dwarf planets, 'micro' planets, companion stars in binary star systems, bodies in asteroid belts and debris fields, and other objects.

Two main types of planet existed: gas giants and rocky worlds. Gas giants were mainly comprised of gaseous layers and did not have a solid surface. Normally, their atmospheres were mostly hydrogen and helium, although a few had oxygen-rich layers capable of harboring life. As very large planets, gas giants possessed powerful gravitational fields. The lower levels of a gas giant's atmosphere were at pressures able to crush any normal starship, and the center of most gas giants was a small, dense metallic core. Rocky planets were much smaller and very varied in nature. Many rocky planets did not have a rocky surface; some of these worlds were covered with water, which could exist as free-flowing oceans or permanent ice fields. On many other rocky planets, the rock had been broken down over time, providing a rich soil that supported a planet-wide arboreal, swampy, or grassy ecosystem. Many terrestrial planets had a range of surface features, including bare rock, free water, and green continental masses with plant and animal life. Others were purely rocky, making them barren and desolate. On some terrestrial planets, industrial or urban development completely removed the original surface and ecosystem, creating an ecumenopolis.

Worlds like Hoth and Mustafar had extreme climates, but still supported life, with their inhabitants having to adapt to their surroundings. Certain planets, such as Dathomir, were strong with the Force, a mysterious energy field created by life that bound the galaxy together. Many traditions suggested that lost worlds beyond the galactic frontier were among the first to discover the Force and its power. "Homeworld" was a term used to describe the original home of a species, organization, or person. For example, Ryloth was the homeworld of the Twi'lek species, and the human species were believed to have originated on the planet Coruscant. The existence of a huge variety of planets that contained a wealth of native species, natural resources, and environments was the underlying reason for most travel, trade, and conflict around the galaxy.

Destroying a planet was possible, although it required a massive superweapon, such as a Death Star, which destroyed the planet Alderaan. It was also possible to turn a planet itself into a superweapon, as in the case of the First Order's Starkiller Base, forged from the planet Ilum, which was capable of destroying entire star systems, such as the ill-fated Hosnian system.

Text and facts from the “Planet” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.