Where Did Water Come From?

Tuesday Feb 25th, 2020


Water. You turn on the faucet, and out it comes. But where did water on Earth originally come from? Some scientists believe that oceans may have been formed (about 8 million years after the formation of planet Earth itself) by water dumped from passing comets, and the recent discovery of a comet containing water with a similar chemical composition to the water all around us on Earth has given support to that theory.

Hartley 2, a comet about 1.25 miles long, contains ice with the same D/H ratio (the proportion of “heavy hydrogen”) as water found in oceans here on Earth. It’s the first time that Earth-like water has been detected in a comet. Hartley 2 probably comes to us from the Kuiper Belt, a sector of space about 30 times Earth’s distance from the sun. Six other comets studied by the scientists contained water with a different composition, and probably originated in the Oort Cloud, about 5,000 times farther away.


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