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The solar system's water: Older than the sun

Water through time: Ices from the parent molecular cloud are incorporated into planet-forming disks around young stars. These ancient ices, including water, are available to nascent planetary systems, including our own. This picture shows the time sequence of water ice, starting in the cloud (prior to the Sun's formation), traveling through the stages of star formation, and eventually being incorporated into the planetary system itself.
[Credit: Bill Saxton, NSF/AUI/NRAO]

Where did the water in our solar system come from? For years, researchers have been debating whether it came from processes that took place after the sun was born, when the planets were just beginning to form--or if it was created much earlier, before a cold cloud of gas even formed the sun. Now, it appears that researchers finally have an answer.

Lauren Cleeves and colleagues designed a model that traces the history of deuterium—a modified version of hydrogen—back through time. They explain that, ever since the sun formed, water in the solar system has been sucking up more and more deuterium. So, the researchers looked at the levels of deuterium in water from all across the solar system—in comets, moons and even Earth's oceans—and they asked their model which scenario of water formation would have led to those current levels.

Their results suggest that the solar system's water could not have formed after the sun did, and that some amount of ice from the cold darkness of space—before the sun was born—must have survived the violent creation of the solar system. If other planetary systems in the galaxy form the same way that ours did, then those systems would have had access to the exact same water as they formed, the researchers say.