It requires time, which depends on distance. After the arrival, there is a chance that from 0 to 50 explorers will die.
Players can see a report in the "Missions" window the moment explorers arrive to a specific sector.
Players can see a message from the Scientific Advisor in the "Events" window only if explorers find anything.
Nebulas are those places, where players can find useful things. There are 4 types of nebulas: