Planets are map objects and resources. Planets are where metal is mined. Metal is the second most important resource in the game, used to build many ships and stations. Species 8472 converts it into biomatter. Planets also provide crew, needed for all ships, and certain stations. The planets must be colonized first to gain crew. Species 8472 does not use crew.
Class D planets are rocky planetoids. They cannot support life, but have a largest amount of metal. They are most likely similar to the planet Pluto
Class HEditClass H planets are dry, making them desert planets, similar to the planet Vulcan. They can support sparse populations, and have a large amount of metal.
Class JEditClass J planets are gas giants similar to Jupiter, Saturn, Uranus, or Neptune. They are the largest planets, and have rich amounts of metal, but cannot be colonized.
Class KEditClass K planets are arctic worlds similar to Rura Penthe. They are probably the least useful planets, since they can only support light populations and have light metal deposits.
Class LEditClass L planets are rocky with high temperatures, similar to class H planets. However, they can harbor more people, but have small metal deposits.
Class M planets are similar to Earth, having a Nitrogen-Oxygen atmosphere and the ability to support large populations. However, they have the least access to metal.