Planets

A planet is a large, rounded astronomical body that usually orbits a star. Planets are featured prominently in the Sagittarius universe, with many important events taking place on numerous planets across the Milky Way Galaxy. Planets come in two main varieties, terrestrial planets and gaseous planets. Terrestrial planets are featured more prominently in Sagittarius, and many important planets in the universe are terrestrial. Some examples include: Earth, Nesta, Trappos, and Archeron.

## Classifications of Planets

### Habitable Planets

Habitable planets are some of the most important planets in the Sagittarius universe. Being habitable for sentient races, plant life, and animal life, they are far more prominently featured than some other planets in the universe. Three of the most important planets in the universe; Earth, Trappos, and Archeron, are habitable. Habitable planets are themselves divided into classes based on their habitability, or in the case of Graveyard planets, previous habitability.

#### Class A Habitable Planets

Class A Habitable Planets are the jewels of the universe, featuring the most biodiversity and habitability of any planet in the galaxy. Planets must have top notch biodiversity, stable biospheres, and no existential threats to their ecosystems to be classified as a Class A Habitable Planet. Class A planets also must feature both land based and water based organisms to be classified as such. There is only one known Class A Habitable Planet known to the current international community as of 2202, Nesta. Earth would have at one point been classified as a Class A Habitable Planet, but when the classification system was created in 2130, Earth was undergoing an extinction event and several existential threats existed on the surface of the planet.

#### Class B Habitable Planets

Class B Habitable Planets are oceanic worlds that are nearly identical to Class A Planets in nearly every aspect except that they lack any significant land-based biospheres. Class A Planets usually have land ecosystems and if a planet is oceanic and doesn't have any terrestrial ecosystems, but have extreme biodiversity in their oceanic environments then they are classified as Class B. A good example of a Class B Habitable Planet is Ceralis, an ocean planet located in the Orion Arm of the Milky Way.

#### Class C Habitable Planets

Class C Habitable Planets are habitable worlds that are either reeling from minor extinction events or have less biodiversity than Class A and B planets in general. Class C, unlike A and B, could apply to either majority ocean planets or planets with both terrestrial and oceanic organisms. Earth itself is classified as a Class C Habitable Planet, as the planet has a moderate level of biodiversity and is reeling from the recent Anthropocene Extinction, caused by the Industrial Revolution and the Space Ages.

#### Class D Habitable Planets

Class D Habitable Planets are planets that are habitable, but have very low biodiversity and a weak biosphere. These planets are usually younger, and just now have life beginning to develop on their surfaces. Earth in its early years would've been a Class D Habitable Planet. Current known Class D Planets include Proxima Centauri B, Ross 128b, and Kepler-186f. The ancient planet of Nampan, used by the Orion Federation as a mining outpost, is a Class D Habitable Planet.

#### Class X "Graveyard" Planets

Class X "Graveyard" Planets are planets that have recently suffered a mass extinction. These planets are usually barren, littered with remains, and mass devastation can be found on their surfaces. Graveyard Planets can have toxic atmospheres, volcanism on their surfaces, or be contaminated by a biological agent. TRAPPIST-1e, the original capital of the Trappist Empire, is a devastated Graveyard planet littered with destroyed cities, lakes choked with debris, and only few surviving Trappists left on the surface. Another Graveyard planet is Archeron, a planet contaminated by the Nano Corusia pathogen that either killed or mutated 89% of its biosphere, causing a mass extinction. Much of the planet is barren and abandoned, with small pockets of flora and fauna, much of which is heavily mutated.

#### Class Z Habitable Planets

Class Z Habitable Planets are planets that are hospitable to life, but have no lifeforms on their surfaces. They are usually very young planets, even younger than Class D planets. Many exoplanets thought to be habitable are examples of these, such as Teegarden's Star b, before it was colonized and inhabited by humans.

### Terrestrial Planets

#### Class A "Airless" Planets

Class A Planets are planets that either completely lack and atmosphere or possess one that is extremely thin. Mercury, in the Sol System, is a primary example of an airless planet.

#### Class O "Oceanic" Planets

Class O Planets are planets whose surfaces are primarily composed of oceans, with very little or no land at all. Examples include Ceralis and GJ 1214b.

#### Class S "Scorched" Planets

Class S Planets are terrestrial planets with surface temperatures exceeding 400 degrees Celsius. Examples include Hades, in the Athena system, and Mercury.

#### Class SV "Venusian" Planets

Class SV Planets are planets with atmospheres primarily composed of carbon dioxide, with crushing atmospheric pressures. They are named after the planet Venus, the first of this type to be discovered. Class SV is a subclass of Class S, since Venusian planets almost always fall into the Scorched class as well.