Explorers go beyond the boundaries of the Federation.  They search for planets with the right conditions to support life.  They don’t try to find out if the planet does have life.  In fact, they’re ordered to check planets from a distance, in case one has intelligent life which might spot them.  From the outside edge of a solar system, they scan the planets.  If they find one with suitable conditions, they report to the membership officer, who sends a survey team.

An explorer called Grenville told Hais and me about his job.  See Report F.