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Water on Earth is found to be older than the Sun

Jenny Winder, News Writer
Sep 29, 2014, 14:10 UTC

Sen—A new study has found that much of our Solar System’s water probably originated as ices that formed in interstellar space. 

Water was crucial to the rise of life on Earth and is also important in evaluating the possibility of life on other planets. Identifying the original source of Earth’s water is key to understanding how life-fostering environments come into being and how likely they are to be found elsewhere. 

Water is found throughout our Solar System, on icy comets and moons, in the shadowed basins of Mercury and in mineral samples from meteorites, the Moon, and Mars. The ices on comets and asteroids in particular, can tell scientists about the ice that encircled the Sun after its birth, the origin of which was an unanswered question until now.

The Sun, in its youth, was surrounded by the solar nebula, from which the planets were born. But it was unclear to researchers whether the ice in this protoplanetary disk originated from the Sun’s own parental interstellar molecular cloud, from which it was created, or whether this interstellar water had been destroyed and was re-formed by the chemical reactions taking place in the solar nebula.

“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,” Conel Alexander of the Carnegie Institution for Science explained.

“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.”

The team, led by L. Ilsedore Cleeves from the University of Michigan, focused on hydrogen and its heavier isotope deuterium. The ratio of hydrogen to deuterium in water molecules can tell scientists about the conditions under which the molecules formed.

Interstellar water-ice has a high ratio of deuterium to hydrogen because of the very low temperatures at which it forms. Until now, it was unknown how much of this deuterium enrichment was removed during the Sun’s birth, or how much deuterium-rich water-ice the newborn Solar System was capable of producing on its own.

The team created models that simulated a protoplanetary disk in which all the deuterium from space ice has already been eliminated by chemical processing, and the system has to start over “from scratch” at producing ice with deuterium in it during a million-year period.

They did this in order to see if the system can reach the ratios of deuterium to hydrogen that are found in meteorite samples, Earth’s ocean water, and “time capsule” comets. They found that it could not, so at least some of the water in our own Solar System has an origin in interstellar space and pre-dates the birth of the Sun.

“Our findings show that a significant fraction of our Solar System’s water, the most-fundamental ingredient to fostering life, is older than the Sun, which indicates that abundant, organic-rich interstellar ices should probably be found in all young planetary systems,” Alexander said.