The Libra and Sagittarius are souvenirs given to Olimar by his two children and are considered mandatory ship parts, yet they seem to be nothing more than two identical jewels on the sides of his ship. By not collecting these parts, you could essentially create a playthrough where Olimar's failure to leave the planet would not be from a lack of a functioning ship, but instead from not being able to live with leaving behind the gifts his children gave him. There's a lot I could say about this game, but this is the thought that sticks out to me the most.