Water Worlds 
Water, water everywhere/Nor any drop to drink.
In “The Rime of the Ancient Mariner,” Samuel Taylor Coleridge’s character was talking about being surrounded by a calm ocean on a sailing ship. But the verse would work just as well on several other worlds of the solar system. Some may host oceans of liquid water that are far more massive than those on Earth. Others may have smaller pools of water. But all of them are hidden beneath crusts of rock or ice.
These water worlds are farther from the Sun than Earth is. At that distance, the raw materials for planets and moons included a good bit of frozen water.
These bits of ice came together with other ingredients to form some of the moons of the giant outer planets. Denser materials, like metals, sank to the centers of these worlds, while lighter materials, like water, bubbled to the top.
Exposed to the cold and vacuum of space, the water at the surface of such a moon remained frozen. But some of the ice below the surface melted from the heat of the moon’s formation, the decay of radioactive elements, or tides caused by the gravitational pull of other bodies.
That’s created global oceans on some of these moons, as well as a possible ocean on the largest asteroid. It’s also created a smaller ocean on another moon of Saturn. So there’s plenty of water scattered throughout the solar system — but not much way to tap into it.
We’ll talk about one of these water worlds tomorrow.
Script by Damond Benningfield, Copyright 2012