Earth's Water Older than the Sun

Most of the water found in our solar system, Earth included, is older than the Sun, likely originating as ices that formed in interstellar space, according to new research. Water was crucial to the formation of life on Earth, and the discovery has implications for the search for other habitable planets as well.

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 interstellar cloud of gas from which the Sun itself was formed.

"Why this is important? If water in the early Solar System was primarily inherited as ice from interstellar space, then it is likely that similar ices, along with the prebiotic organic matter that they contain, are abundant in most or all protoplanetary disks around forming stars," researcher Conel Alexander from the Carnegie Institution explained in a statement.

"But if the early Solar System's water was largely the result of local chemical processing during the Sun's birth, then it is possible that the abundance of water varies considerably in forming planetary systems, which would obviously have implications for the potential for the emergence of life elsewhere."

To settle the debate, researchers created computer models that compared ratios of hydrogen and its heavier isotope, deuterium, which has been enriching the solar system's water over time. In order to reach the ratios of deuterium to hydrogen that are found in meteorite samples, Earth's ocean water, and icy comets and moons, at least some of the water would have to have been formed before the Sun's birth, according to the study. But they found that that was not the case. Their protoplanetary model used, which was essentially starting from scratch, was unable to meet the correct ratios, which told researchers that at least some of the water in our own solar system originated in interstellar space and pre-dates the birth of the Sun.

The findings were published in the journal Science.