THERE'S water, water, everywhere in the cosmos, but how it comes about in the interstellar clouds that give birth to stars, planets and even life is a bit of a mystery. The answer, it seems, may lie on the surface of frosty dust grains.
When hydrogen and oxygen exist as gases water forms easily, but models of interstellar clouds suggest that this route is unlikely to produce the abundance of water seen in them. Most of the water we see has formed icy sheaths around tiny grains of dust in the clouds, and it is believed oxygen atoms accumulate on the grains and react with hydrogen to form water.
Akira Kouchi and colleagues at Hokkaido University in Sapporo, Japan, tested the idea by freezing oxygen onto a nucleation surface held at 10 degrees above absolute zero. When they fired atoms of hydrogen onto the oxygen, hydrogen peroxide was produced, which in turn reacted with more hydrogen to produce water. These reactions happened fast enough to explain the amounts of water found in interstellar clouds (Chemical Physics Letters, DOI: 10.1016/j.cplett.2008.02.095).
Paola Casselli at the University of Leeds says it's an important first step, but points out the team in Japan used O2 molecules, which are less common in interstellar clouds than single oxygen atoms.
Astrobiology - Learn more in our out-of-this-world special report.
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