177. What moon is thought to have broken apart and reaccreted? Why do we think this happened? 178. Why was Neptune predicted to exist? How was it discovered? 179. On what planet is the Great Dark Spot found? What is it and is it a permanent feature? 180. What is unique about Triton”s orbital motion around Neptune? 181. What is the composition of the geysers seen erupting on Triton? 182. Why did scientists think that Neptune was surrounded by ring arcs? What did Voyager 2 reveal regarding this issue? 183. How are the orbital properties of Pluto different from the other planets? 184. What is the surface and atmospheric composition of Pluto? 185. How has the discovery of Charon increased our knowledge about Pluto? 186. What have observations from the Hubble Space Telescope revealed about the surface of Pluto? 187. What is Eris? 188. Why are Pluto, Eris, and Ceres called dwarf planets?