Planet is the common designation for a certain type of celestial body usually orbiting a star. They occurred in a great variety of different compositions, masses, and surface conditions. The exact definition of what constituted a planet varied among cultures.

The final appearance of a planet depended on its formation process, which meant where and under what circumstances it formed. Planets could accumulate gigantic atmospheres, exceeding their original size and mass, or they could rest without any atmosphere at all. With a sufficient mass, a planet was able to accumulate so much gas, that it started to undergo nuclear fusion, turning into a protostar. In this state it began to emit energy, as its core temperature and density increased. Planets could also be changed to a Class M environment by terraforming. (TNG: "Home Soil")

The Federation had numerous different classifications for planets depending on their mass, composition, surface environment and atmospheric compounds.

Gas giant
Ring planet
Rogue planet


All planets are collected in the category Planets. Additionally, several lists for specific groups of planets exist:

Cardassian planets
Dominion planets
Earth colonies
Federation colonies
Federation members
Inhabited planets
Klingon planets
Delphic Expanse planets
Romulan planets
Uninhabited planets
Unnamed planets

Prime planets
First planets
Second planets
Third planets
Fourth planets
Fifth planets
Sixth planets
Seventh planets
Eighth planets
Ninth planets
Tenth planets
Twelfth planets
Fourteenth planets
Twentieth planets
A planet is a celestial body that

1. It orbits around the sun.

2. It has? sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

3. It has cleared the neighborhood around its orbit.

Several problems with this definition immediately pop up for astronomers.

Under the IAU criteria, the more than 300 extrasolar planets identified to date would not be considered planets.
Technically, there was never a scientific definition of the term Planet before 2006. When the Greeks observed the sky thousands of years ago, they discovered objects that acted differently than stars. These points of light seemed to wander around the sky throughout the year. We get the term "planet" from the Greek word "Planetes" - meaning wanderer.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License