I believe the particulate space matter is the official explanation.
I think it’s frozen urine crystals from Riker flushing the head.
Since its slipping up over the front of the ship, its most likely from the loos in ten forward 
Really? That’s boring. ![]()
It occurs to me that it could just be some of the millions of tiny needles that were launched into space in the 20th century.![]()