When the Curiosity rover discovered evidence of an ancient stream bed on Mars in late September, it was an important and reassuring discovery. In fact, scientists have found increasing evidence of water on numerous moons, planets, and asteroids in recent years—an encouraging trend for those who see the familiar substance as the backbone of a future space-based economy.
By harvesting water and converting it into a hydrogen-based rocket fuel, a space mining company like Shackleton Energy of Austin, Texas, could become the Exxon Mobil of the interplanetary highway.
“If they can figure out the engineering and the economics, the raw materials are out there,” says planetary scientist Andrew Rivkin of Johns Hopkins University.
Here are six of the more interesting water worlds and the prospects for each.