Once is accident; twice is coincidence. This reeks of enemy action. Who, why, and how? (Where and when are at least partially obvious - right here, right now - and what depends on what's being asked. Could be the planet/moon, could be the ships, could be cargo. Could even be something so off-the-wall that the players aren't going to be able to guess without learning some or all of the other answers...)
As I said, this could easily be the springboard into something a lot wider-ranging. A twist on piracy the players haven't seen/encountered before? A subtle opening gambit in a war? Alien action, possibly but not necessarily combined with the previous options? A natural hazard? A previously unheard-of animal encounter, with an equally unheard-of ability to do this? All sorts of possibilities, I see.