ScienceShot: Where Did Water Come From?

Water, water everywhere—but where did it come from? From icy comets to Earth's vast oceans, our solar system is chock full of water, yet so far no one has been able to demonstrate how it formed in the first place. Getting atomic oxygen and molecular hydrogen to combine in the deep, cold vacuum of space is nearly impossible. Scientists think the answer may lie in a dusty interstellar cloud, like the one shown here. A team reports today at a meeting of the Royal Astronomical Society in Glasgow, United Kingdom, that each grain of interstellar dust provides a reactive surface on which wayward hydrogen and oxygen can combine into H2O. Eventually the two elements form an icy coating on the grain, the grains in the cloud condense gravitationally, and presto! Comets, icy moons, and seas galore.