Up to Half of Earth’s Water May Be Older Than the Sun

Up to half of Earth’s water may have formed in interstellar space before the Sun and survived the birth of our solar system.

Astronomy

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Some of the water on Earth may have an astonishingly old history. A 2014 study modeled the chemistry of water in the cloud of gas and dust that eventually formed our Sun and solar system, and found that up to roughly half of the water could have existed before the Sun itself formed. The idea is that water ice formed in extremely cold interstellar space and some of that material survived the violent process that created the young solar system. Researchers used the amount of deuterium, a heavier form of hydrogen, as a chemical clue. The model found that the young planet forming disk around the Sun could not easily produce the observed amount of heavy water on its own, pointing to an older interstellar contribution. This does not mean every water molecule on Earth has remained intact for more than 4.5 billion years. Water is continually involved in chemical and biological processes, so the age of a particular molecule is different from the age of the hydrogen and oxygen atoms that make it up. The broader finding is important because water ice is now known to be widespread in interstellar clouds, suggesting that young planetary systems may inherit water from the same kinds of cold cosmic reservoirs. Modern observations continue to find extensive water ice in star forming regions, reinforcing the idea that water is a common ingredient available before planets fully take shape.

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