DECEMBER 2009 IN
RICK ASTER’S WORLD

Water Is Universal

Recent observations of water on the surface of the moon tell us that water is not the rare property of Earth-like planets and comets, as was previously thought. Instead, we find that water is one most common chemical compounds in the universe.

This makes some sense when you consider that water is a simple three-atom molecule, in which two of the atoms are hydrogen, far and away the most common element in the universe, and the other is oxygen, not a rare element either. But in actual practice, when hydrogen and oxygen cross paths, how easily do they combine?

Earlier this year, scientists observed water forming and evaporating every day on the lunar surface. The water evaporates when the sun is brightest, but forms in layers several molecules thick when the sun is lower in the sky. Water apparently forms as hydrogen atoms expelled by the sun react with dust on the moon. Dust is formed mostly from oxides, and oxygen atoms released by the oxides combine with the solar hydrogen to form water.

If this happens every day on the moon, it also happens in many other places, wherever dust and stars are near each other — which is basically everywhere. That tells us that water is forming continuously everywhere in the universe.

Water may be forming everywhere, but how long does it last? A second observation found a significant body of water — frozen to form ice — in a shaded area of the moon. Some of this ice was thrown loose by the impact of the discarded section of a rocket, and the spectral analysis of the debris matched the distinctive signature of water.

This result suggests that water does not decay quickly on its own, and will accumulate if given a chance. It suggests that desert planets such as Venus and Mars, Earth-like in many respects but relatively lacking in water, may not be the norm, as previously thought.

Most of all, though, what this says is that humans will not be trapped on Earth by a cosmic water shortage. There are many obstacles to be faced before we can go traveling around the galaxy, but a shortage of water is not likely to be the limiting factor.


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