The skeptic in me has me thinking meteorite or space debris entering the Earth's atmosphere. But for something that bright, it would have to have been a rather large object. There is always the possibility of it being some sort of alien spacecraft (perhaps it was part of the cast from Close Encounters which was released two years after Jaws) but given the trajectory I highly doubt it. Still I find it interesting that this was left in the shot. Perhaps Spielberg didn't see it at the time and decided to leave it in instead of having to reshoot.
