If money were no object, many of us might fix up an old car or remodel the house. Millionaires and billionaires use their fortunes to build spaceships, pursue immortality, create island nations, or mine asteroids. Looking for new challenges can boost their profiles, too — Tesla founder Elon Musk, of course, just bought Twitter for a mere $44 billion. But that's not the only thing he's spent some serious loot on. Here's a look at 13 eccentric projects of the rich — many fortunately tilting toward advancing science, especially in our oceans or outer space — because you're not truly a member of the club without one.