3,5/5. Good little mysteries for kids. I find the story a bit slow for a young public, it didn't happen that much stuff in it. The characters are alright, but the best part for me was the educative part, a kid would learn a bit about planets and our solar system. The clue are presented slowly, so you can try to solve them by yourself before continue to read, or just read through it and learn the answer straight ahead. Nothing extraordinary, but a book that does a good work in many ways!