A degree of realism to this game: The 4 nodes included in the mapgen are pretty similar to what you'd find on the moon in real life. This works well as a short collection game, but isn't really interesting. The title is sort of false advertising, as there is no secret to find :) In the future, it would be interesting to incorporate more elements so that the game is playable for longer.
Additionally, there is currently a crash you can make by clicking the jackhammer on many nodes very quickly.
Yes it was good to learn about the moon's geology as I made the project. Sadly there was no time to actually incorporate secrets, so the 'secret', if there is any, is the material analysis, which in the game's story takes place after the game actually ends..
I'm aware of the crash as it happened to me several times in development. I'm not sure how I can avoid it outside of filling the code with nil checks, but if I can fix it I might learn a fair bit about Minetest.