A Class-M Planet was a designation for any world with a very thin atmosphere, cold climate, and extremely thin atmosphere. The “M” is derived from Mars, which is the model for the class. Class-M worlds are also known as “cold deserts.”
Average atmospheric pressure: 4-100 millibars
Typical atmospheric content: 60-99% carbon dioxide
Diameter: 5000-9000 km
Average temperature range: -300◦ – 30◦ C
Gravity: .25 – .6g
Typically defined by low surface water content, except at the poles. Dry ice is common on some planets. Though most Class-M worlds have no magnetic field due to solid cores, this is not always the case. Farigha, as an example, has a magnetic field, making it more ideal for terraforming than Mars.