Which came first, Earth's water or the sun?

Water found in Earth's oceans, in meteorites and frozen in lunar craters predates the birth of the solar system, a study published on Thursday shows, a finding with implications for the search for life on other planets.

Scientists have long debated whether the solar system's water came from ice ionized during the formation of the solar system, or if it predated the solar system and originated in the cold interstellar cloud of gas from which the sun itself was formed.

The study was published in this week's issue of the journal Science.

"It's remarkable that these ices survived the entire process of stellar birth," lead researcher Lauren Cleeves, told Reuters.

Cleeves, a doctoral student at the University of Michigan, had been studying how radioactivity, galactic cosmic rays, and other high-energy phenomena impact planet-forming disks of matter that circle young stars.

The "aha" moment, she said, was realizing that conditions in the early solar system weren't right for synthesizing new water molecules.

"Without any new water creation, the only place these ices could have come from was the chemically rich interstellar gas out of which the solar system formed," she said.

To prove the point, she and colleagues ran computer models comparing ratios of hydrogen with its heavier isotope, deuterium, which has been enriching the solar system's water over time, as the Monitor's Claire Felter explains.... 

Cleeves's team couldn't go back in time to observe our solar system's dust disk, so instead they observed stars that are forming today and modeled the conditions of their disks to calculate which scenario was right.

Using samples of "heavy water" ices, which contain high levels of a heavy isotope of hydrogen called deuterium, Cleeves and her colleagues worked backward to see if conditions in the solar nebula could have yielded the current measurements of heavy water in the solar system.

It turned out that the first scenario, where the solar nebula produced our water's current levels of deuterium on its own, had to be crossed off the list.

"The punch line was that heavy water was just not produced abundantly," says Cleeves. "It didn't even sort of tip the scale at all."

To reach the ratios found in meteorite samples, as well as in Earth's ocean water and comets, at least some of the water would have had to be formed before the sun's birth, the scientists concluded.

The process likely would be the same for other solar systems as well, suggesting conditions hospitable for life could exist beyond Earth.

Also this week, a second paper in Science notes the discovery of a branched carbon-containing molecule involved in the creation of stars.

The molecule, known as iso-propyl cyanide (i-C3H7CN), was discovered in a giant gas cloud called Sagittarius B2, the most massive star-forming region in the Milky Way, by Chile's ALMA observatory.

"Understanding the production of organic material at the early stages of star formation is critical to piecing together the gradual progression from simple molecules to potentially life-bearing chemistry," lead researcher Arnaud Belloche, with the Max Planck Institute for Radio Astronomy in Germany, said in a statement.