Up to about half of the water on Earth is apparently not just older than the planets in our solar system, but older than the sun itself, suggests a team of astronomers from the University of Michigan.

The new findings, published in the journal Science, sheds new light on the origins of the water on the earth and its planet neighbors.

While some scientists have speculated molecules in comet ices and terrestrial oceans were created with the system itself, within the planet-forming disk of dust and gas that circled the new sun 4.6 billion years ago, others have suspected the water formed much earlier, from the molecular cloud that birthed the sun and its planet-forming disk, explained a university news release.

Ilse Cleeves, a doctoral student in astronomy at the U-M College of Literature, Science, and the Arts, indicates between 30 to 50 percent of the solar system's water was actually derived from the older molecular cloud -- roughly a million years before the solar system.

Cleeves and Ted Bergin, a professor of astronomy, arrived at their mind-bending conclusion by simulating the chemistry that occurred while the solar system was forming.

Specifically, the team focused on the ratio of two slightly different varieties of water, the common kind and heavy water, which contains a larger than normal amount of the hydrogen isotope deuterium, instead of the common hydrogen-1 isotope that makes up most of the hydrogen in so-called normal water.

It's been found that comets and Earth's oceans hold ratios of heavy water that are higher ratios than that of the sun.

That means, said Bergin, "that Earth received a contribution of water from some source that was very cold -- only tens of degrees above absolute zero, while the sun being substantially hotter has erased this deuterium, or heavy water, fingerprint."

To test their ideas, the scientists "wound back the clock and zeroed out the heavy water," they said, in their solar system simulation, and then hit "go" and waited to see if the computer-generated eons of solar system formation would lead to the ratios of water seen today.

"We let the chemistry evolve for a million years-the typical lifetime of a planet-forming disk-and we found that chemical processes in the disk were inefficient at making heavy water throughout the solar system," Cleeves said. "What this implies is if the planetary disk didn't make the water, it inherited it. Consequently, some fraction of the water in our solar system predates the sun."

That said, since all life on Earth depends on water, understanding when and from where it came could help scientists better understand how common water might be throughout the galaxy.

Based on the U-M researchers' simulations and growing astronomical understanding, "the formation of water from hydrogen and oxygen atoms, is a ubiquitous component of the early stages of stellar birth," said Bergin. "It is this water, which we know from astronomical observations forms at only 10 degrees above absolute zero before the birth of the star, that is provided to nascent stellar systems everywhere."

Said Cleeves: "The implications of these findings are pretty exciting ... If water formation had been a local process that occurs in individual stellar systems, the amount of water and other important chemical ingredients necessary for the formation of life might vary from system to system. But because some of the chemically rich ices from the molecular cloud are directly inherited, young planetary systems have access to these important ingredients."