As soon as I saw "second rock from the", I knew the top-level answer was going to be "Venus". At first I felt frustrated that it wouldn't let me enter the solution, but if it had accepted that then I would have missed out on the rest of the puzzle. In retrospect, I felt like having to work backwards from "Venus" and "sun" to figure out the lower-level clues was much more interesting then if it had just let me skip those clues.