In the first episode of Star Trek ever aired on television, on September 8, 1966, the spaceship Enterprise visits an archaeological excavation site on the planet M-113. The planet is covered by a desert with sparse vegetation and ruins of a former civilization. The atmosphere is apparently breathable by humanoids, a plot device adopted in many later episodes. In the third episode, confusingly enough filmed as a pilot, the crew of the Enterprise under the command of Captain Pike is stranded on the planet Delta Vega, a planet similar to Earth except it slightly smaller size, with a lithium cracking station operating there. The set of the barren and rocky landscape was recycled from the episode (and rejected original pilot) “The Cage.” In 79 episodes of Star Trek – The Original Series the Enterprise will visit many planets, sometimes inhabited by humanoids or by alien lifeforms. The classification of planets in the Star Trek universe is based on size (gas giants or small, rocky worlds), composition (rock-metal core or gas), geological activity (inactive- active), atmosphere (from oxygen-rich to toxic) and comprises fourteen planet types. For example planets suitable for humans, small, rocky worlds with some geological activity and oxygen-atmosphere, are classified as M after Minshara, the native name of Vulcan, homeworld of Commander Spock. Aboard the Enterprise Spock can easily scan and classify a planet. In reality, the first exoplanet was discovered in January 1992 and today more than 3,700 planets in other star systems are known. However, we can only speculate about the environment found on an exoplanet. The shape of the orbit can be used to calculate the mass of an exoplanet. Knowing the mass it is possible to calculate the gravitational force on the planet’s surface and determine if it can hold an atmosphere. The distance and type of star in the alien star system can provide clues about the temperatures found on the planetary surface. New advanced observation methods made it possible, in some cases, to observe the atmosphere of an exoplanet and identify the chemical composition.
In the 2011 published paper Taxonomy of the extrasolar planet the following planet classification system is proposed:
– Class F: Planets of the “freezing class” are covered by ice and snow.
– Class W: Planets of the “water class” are like Earth, orbiting a star in the habitable zone where temperatures allow liquid water to exist.
– Class G: The “gaseous class” is too hot for solid or liquid water to exist, but eventually the planet possesses an atmosphere.
– Class R: The orbit of a “roasters class” planet around its host star is so narrow, that the resulting planetary surface temperature is high enough to melt rocks.
– Class P: “Pulsar class” planets orbit the collapsed remains of a star and are constantly bombarded by high radiation and exposed to strong magnetic fields.
M-Planets are common in the Star Trek universe. In the real world, we have discovered only few planets that may host liquid water, an important ingredient of life as we know it, as their small size makes them hard to detect. Desert-Planets are among the most visited by the crew, a plot device to limit costs of the film set. However, the Enterprise visits also Ice-Worlds and Lava-Planets. Star Trek aired three years before the first manned Moon landing and virtually nothing was known about the geology of other planets or moons. Yet the authors of Star Trek got many things right. Small ice moons are very common and the Jupiter moon Io is also geologically very active, with a surface covered in sulfuric lava. In the episode “The Naked Time” the Enterprise is orbiting Psi 2000 to observe the disintegration of the planet. The doomed world is completely covered in ice and snow. Geological evidence suggests that almost 650 million years ago also our planet became temporally a “Snowball Earth.” How this happened is unknown, but the release of gases by volcanoes probably saved the planet and the first terrestrial life forms as the planet warmed due the greenhouse effect of the carbon dioxide gas. It is curious to note that chief medical officer McCoy discovers unknown organic molecules in the ice of Psi 2000. Some sort of geological activity is believed to be necessary to host complex life. Hot springs can provide nourishment and energy to simple life forms and tectonic activity, like mountain building, can benefit evolution as the life forms need to adapt to the changing environment.