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Class M

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The Minshara class planet Earth

In the Federation standard system of planetary classification a Class M planet, moon, or planetoid was considered to be suitable for humanoid life. By the mid-24th century, thousands of Class M planets had been charted by the Federation. These worlds were the first choice for colonization. Since the late 23rd century, the Federation has been terraforming lifeless worlds into Class M worlds. Environmental conditions on Federation starships mimic the Class M environment. (TOS: "The Cage"; TNG: "Justice", "Home Soil", "Final Mission"; VOY: "Caretaker")

During the mid-22nd century, Vulcan science used the term Minshara class for such planets. Vulcans were not able to determine if a planet was Minshara class through orbital scans, instead sending down probes to collect the necessary data. (ENT: "Strange New World"). In 2151, Starfleet officers were not familiar with the term and Enterprise chose to adopt it. However, by 2154, Starfleet had adopted the term Class M. A century later the term was in general use in Starfleet, even though the term "Earth-type" was also occasionally used.

By the 23rd century it was theorized that there was a mathematical probability of three million Earth-type planets in the Milky Way Galaxy alone. (TOS: "Balance of Terror")

A planet could fall within the range of the M-class classification. This range was from 1 to 4. The Koinonian homeworld was an example of a M-class type 4 planet. (TNG: "The Bonding", "Clues")


Background information

  • The term "class M" was first used in "The Cage" to describe the planet Talos IV. The variant "M class" is also often used. The term has become Star Trek shorthand for Earthlike, and due to obvious production practicalities is the "default" for planetary surface scenes.
  • The Vulcan term Minshara class (first used in ENT: "Strange New World") was used in Enterprise to denote planets that in other series would have been called class M by the writers, the implied consequence being that the two terms meant the same, and possibly even that M stood for Minshara. This assumption has been contested by some fans, but is at least supported by the Star Charts. From an in-universe standpoint The term M-class was first seen chronologically in a text within the Handbook of Exobiology in "Strange New World", the same episode that introduced Minshara class. However, this mention was barely legible on-screen and may have been included by an art department not yet aware of the intention to use "Minshara class". The first spoken use of the word was in ENT: "Home", where Archer used it to describe Archer IV, a planet implied (but not confirmed) to be Minshara class in ENT: "Strange New World".
  • Spock called the planet from TOS: "Return to Tomorrow" class M despite the atmosphere being ripped away, suggesting that class M goes beyond being able to support life. Alternately, he could have been saying that the planet prior to losing its atmosphere would have been categorized as class M.
  • According to the Star Trek: Star Charts, class M planets have ages that range from three to ten billion years and a diameter between 10,000 and 15,000 kilometers. They are located within the ecosphere of a star system.


  • The novel Strangers from the Sky indicates that the term "Class M" was used by Humans prior to First Contact with Vulcans, or indeed before humanity reached any extra-solar planets.

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