The Planet Raid feature can be found in the Battles Section and it allows you to extract Dark Matter and other resources with your Planetary Extractor Module. You must have an unoccupied planetary extractor to attempt a raid.
Dark Matter is usually the most prominent matter to get here, but you can also extract Cold Matter, Omega Matter, and Prime Matter. The amount of matter available depends on your Planetary Extractor level and the fleet present.
Planet Raids offer 3 different Enemy Fleets at a time. The strength of these fleets are based according to the Elo rating of the first Fleet's Fleet Raid
Every time you defeat a fleet and start an extraction, the available fleets will refresh, offering you 3 new opponents with different amounts of matter.