Class M is a term commonly used in Star Trek to describe planets that are environmentally similar to Earth. The term may derive from the Vulcan designation of "Minshara-class" that was once used in Star Trek: Enterprise.
Class M planets have the following features in common:
- Gravity of approximately 1 G.
- An atmosphere that is over 70% nitrogen, around 20% oxygen, and otherwise non-toxic to humanoids.
- Large bodies of water.
- A climate that is suitable for humanoid life and other flora and fauna that are typical of Earth life.
Most Class M planets already support life of some sort, and many are home to native humanoid civilizations.