From Destinypedia, the Destiny wiki
Destinations are locations that players can travel to from the Director. This primarily includes PvE locations and social spaces; Crucible locations are normally selected at random and cannot be visited during matchmaking except in private matches. PvE Destinations are the largest playable spaces and have a large number of activities available, namely: Patrol, Story Missions, Strikes, and Raids.
Note: Despite being separate from Mars, Phobos is accessible from the Meridian Bay destination screen.
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