Rosseau V was the fifthplanet of the Rosseau planetary system. This planet had an asteroid belt located around or near it. The region was unique in that it was surrounded by neutrino clouds that formed a harmonic resonance. Eventually the resonance becomes synchronous, making the place sound like it "has a voice."
The script spelling for this planet "Rosseau V", however several other sources, including the Star Trek Encyclopedia, as well as the episode's closed captioning, spell it as "Rousseau V."
Visual Effects Supervisor Dan Curry used lava rocks he found in the buildings supply for this scene. He was very careful sorting the right rocks out. (TNG Season 2 DVD special feature "Departmental Briefing Year Two: Memorable Missions - The Dauphin")