Water found in Earth's oceans, in meteorites and frozen in lunar craters predates the birth of the solar system, according to a study published on Thursday.
The finding has implications for the search for life on other planets.
Scientists have debated for a long time whether the solar system's water came from ice ionized during the formation of the solar system, or if it originated in the cold interstellar cloud of gas from which the sun itself was formed.
The study was published in the most recent edition of the journal Science.
"It's remarkable that these ices survived the entire process of stellar birth," lead researcher Lauren Cleeves, a doctoral student at the University of Michigan, told Reuters.
Cleeves had been studying how radioactivity, galactic cosmic rays and other high-energy phenomena impact planet-forming disks of mater that circle young stars, according to a Carnegie Science news release.
She added that the big moment 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," Cleeves said.
In order to prove the point, Cleeves and her colleagues ran computer models comparing ratios of hydrogen with its heavier isotope, deuterium, which has been enriching the solar system's water over a period of time, according to the release.
Some of the water would have had to be formed before the sun's birth in order to reach the ratios found in meteorite samples, as well as in Earth's ocean water.
The process would most likely be the same for other solar systems, meaning conditions hospitable for life could exist beyond Earth.
A second paper released this week in Science points out the discovery of a branched carbon-containing molecule involved in the creation of stars, according to the release.
The molecule, also known as iso-propyl cyanide, was found in a gas cloud called Sagittarius B2, the largest 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, according to the release.
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