considering Bungie originally described the Fallen as spider pirates I think something along these lines is likely. Also think about the opposite: imagine a human ship that is raided by the Fallen near Saturn, the distress signal going out to Earth is going to take way too long to be effective, so it is up to you and the other guardians in the area to work together as "first responders" and protect the supplies and lives of the men and women on the ship.