Will we find extraterrestrial life on Mars, Europa, or an exoplanet like Earth? Or will it be on an entirely different kind of planet, larger than the Earth, smaller than Neptune, and with planet enormous quantities of water? These hydrogen-rich ocean worlds, or hycean worlds, may be habitable. And to keep our own planet habitable, we may need to think about gently nudging asteroids off a collision course rather than blasting them to smithereens.