Sorry your browser is not supported!

Class A
Class A, or "Geothermal", planets are small, young worlds with surfaces that are usually molten with possible volcanic activity. Atmospheres, if any, would be very thin. This is similar to the moon Io.

Class B
Class B, or "Geomorteus", planets are young planets that are larger than Class A. They could have partially molten surfaces and may have active volcanoes. Atmospheres, if any, are very thin. In our real solar system Mercury may be considered a Class B planet although it has no volcanoes.

Class C
Class C, or "Geoinactive", planets are young planets that are geologically inactive (hence their name), and may be covered in ice and/or frozen gases. In our real solar system Pluto could be considered a Class C body. In the series, the planet Psi 2000 from the episode "The Naked Time" was Class C.

Class D
Class D objects are asteroids and moons. Some may also be so-called dwarf planets. They are small and geologically inactive. Atmosphere, if any, would be very thin. Earth's Moon could be considered Class D. Regula from the movie Star Trek II: The Wrath of Khan was a Class D planetoid.

Class E
Class E, or "Geoplastic", planets are small, young and volcanically active worlds still in the process of forming. Their surfaces are largely molten. In the series, the planet Excalbia in the episode "The Savage Curtain" was considered Class E.

Class F
Class F, or "Geometallic", planets are very young worlds with volcanically active surfaces with heavy metallic cores rich in ores and minerals making them valuable to mining conglomerates. If any life develops it may be silicon-based as it is in the case of Class F planet Janus VI, from the episode "The Devil in the Dark".

Class G
Class G, or "Geocrystalline", planets are young but large worlds, with surfaces that are still solidifying. Their atmospheres may contain carbon dioxide and other toxic gases. If there is any life present it would be limited to primitive single-celled organisms. In the series, the planet Delta Vega, from the episode "Where No Man Has Gone Before", is considered Class G.

Class H
Class H planets are desert worlds with barren surfaces that are either hot and arid (if in close orbit of the parent star), or covered with icy tundra if in a more distant orbit. Life forms developing on such a world would have to be resilient to either extreme hot or cold temperatures and if the planet is close to the star, resistant to solar radiation. Various worlds featured in the series, such as Rigel XII (from "Mudd's Women"), Tau Cygna V (from "The Ensigns of Command"), Ocampa (homeworld of the character Kes and seen in the episode "Caretaker"), and Nimbus III (from Star Trek V: The Final Frontier) can be considered Class H planets.

Class I
Class I planets are Gas Supergiants, over 140,000 km in diameter. They are comprised almost entirely of hydrogen and helium, but may contain water vapor as well. They may contain a solid metallic mass core and radiate heat. They can have hundreds of moons and also water ice rings. Many extrasolar planets discovered in real life could be classified as Class I Supergiants.

Class J
Class J planets are Gas Giants less than 140,000 km in diameter. They are mainly comprised of hydrogen and helium gases and could have a solid rocky or metallic core. They can have many moons as well as water ice rings. In real life, Jupiter and Saturn could be Class J planets.

Class K
Class K, or "Adaptable", planets are rocky and barren with little, if any, surface water. Their atmospheres are thin, and comprise mostly carbon dioxide. Life forms, if any, are limited to single-celled organisms and algae. They are "adaptable" because through terraforming they are suitable for human colonization. In real life, Mars could be considered a Class K planet. In the series the planet Mudd, from the episode "I, Mudd", is Class K.

Class L
Class L, or "Marginal", planets have rocky, barren surfaces with little water. Their atmospheres are mainly oxygen and argon with high concentrations of carbon dioxide. Life forms, if any, would be limited to simple plant life. Class L planets are suitable for human colonization with some terraforming. In the series, the planets Indri VIII (from "The Chase"), and possibly Borg assimilated worlds are Class L.

Note: Earth may have become a Class L planet, as was seen briefly in the time conduit in Star Trek: First Contact, after the Borg altered the timeline and assimilated it.

Class M
Class M, or "Terrestrial", planets are the most commonly visited planets in the Star Trek series. They are named after the Vulcan term "Minshara" class. They are always located in the ecological region of a star where they are provided enough warmth and energy to develop and sustain carbon-based life. Their surfaces comprise a thin tectonic layer floating on a molten rock mantle and they usually have many active volcanoes. Most importantly, they have plenty of liquid water necessary for life to exist. Their atmospheres contain oxygen and nitrogen with other trace gases. Life forms are almost always present, often flourishing as extensive plant and animal life. Usually a sentient race is also present. Earth is a textbook example of a Class M world. Other worlds in the series such as Vulcan, Cardassia Prime, Risa (initially seen in "Captain's Holiday"), Bajor, and Qo'noS are Class M planets.

Class N
Class N, or "Reducing", planets are barren and rocky with extremely high surface temperatures caused by an intense greenhouse effect. Their atmospheres are extremely dense comprising mainly carbon dioxide and corrosive sulfides. Sometimes water vapor is present. Life would be limited to single-celled organisms living in the upper layers of the atmosphere. In our real solar system, Venus could be a Class N planet. Some Class N planets may also fall into Class X, Y, or Z Demon planets, especially if a bizarre form of life exists on them.

Class O
Class O, or "Pelagic", planets are similar to Class M worlds but over 80% of their surface is covered in water. Life forms would mainly be aquatic in nature. In the series, Argo (from "The Ambergris Element"), and Pacifica (from "Manhunt") are considered Class O planets.

Class P
Class P, or "Glaciated", planets are similar to Class O water planets with an abundance of surface water; however, almost all of it is locked in frozen ice. Liquid water may be present under the ice but at extreme depths. Any life developing on the surface would have to adapt to extremely frigid conditions. In real life, the Jovian moons Europa, Callisto, and Ganymede could be considered Class P. In the series, the planets Exo III (from "What Are Little Girls Made Of?"), The Andorian homeworld, and the Breen homeworld (allegedly) fall into this classification.

Class Q
Class Q, or "Variable", planets have variable surface conditions because they either orbit a variable star (whose power output fluctuates), or their distance from their primary star varies greatly due to a sufficiently eccentric orbit. The result is a world where temperatures fluctuate within extreme levels. Any life existing on such a world will have adapted to rapid climate changes. A Class Q designation might also be applied to planets whose conditions vary due to other effects, either natural or artificial: for example, the planet Meridian in the Gamma Quadrant might be considered Class Q as the planet shifts between dimensions, existing as solid matter and then as energy for unequal periods of time.

Class R
Class R, or rogue, planets do not orbit stars. Instead, they float in the cold darkness of space. They most likely normally formed within a solar system but have been flung deep into space, usually due to a collision with another planetary body. The surface of a rogue planet would usually be barren, but some might be temperate due to geothermal venting with atmospheres filled with volcanic gases. Life would be rare, but some may have unusual life that gather near volcanic regions (similar to how deep ocean life thrives near volcanic vents on Earth). The surface life would exist in complete darkness with plant life that is non-photosynthetic in nature. In the series, the planets Dakala (from "Rogue Planet"), the Founders' homeworld, and Gothos, (as it was used under the control of the Trelane entity in the episode "The Squire of Gothos"), are rogue planets.

Class S and T
Class S and Class T, or "Ultragiant", planets are Super Gas Giants or brown dwarfs. Their diameters range in size from 10 to 50 million km (Class S) and 50 to 120 million km (Class T). Any larger and they would be classified as stars. They radiate considerable heat and generate enormous amounts of gravity, often harboring hundreds or even thousands of moons. In most cases, these moons would be subject to considerable tidal forces and gravitational effects caused by their parent planet - oceans or other large bodies of water would experience gigantic waves and powerful currents. In real life, some recently discovered extrasolar planets could classify as Class S or T Ultragiants.

Class X, Y and Z

Classes X, Y, and Z are reserved for strange planets referred to as "Demon" worlds where surface conditions do not fall into any other recognized category. Such worlds are usually hostile and lethal to humanoid life. If life develops on these worlds they usually take on many bizarre forms, like living crystal or rock, liquid or gaseous physical states, non-corporeal or dimensional states or energy-based. In the series, the planet Tholia, the "Silver Blood" planet discovered by the USS Voyager in the Delta Quadrant in the episode "Demon", and the home world of the incorporeal Medusan species are considered Demon planets.