A mother buys a whole set of video tapes of children’s story cartoons for her child. One day, the excited child watches the cartoons when the parents go out. However, surprisingly, the video tapes include one program Blue Beard which is not mentioned in the written catalogue. When the story is shown on TV, the child feels amazed. He is so surprised that his mouth is open. Blue Beard indeed leaves an indelible impression on him.
Focus：The Roche limit (the term is named after Édouard Roche who first calculated the theoretical limit in 1848) is the distance within which a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body’s tidal forces exceeding the first body’s gravitational self-attraction. Inside the Roche limit, orbiting material will tend to disperse and form rings, while outside the limit, material will tend to coalesce.