Class-M Planet

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.”

Defining characteristics:

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.