The Water On Earth Predates The Formation Of The Sun

Bill Saxton, NSF/AUI/NRAO. Much of the water in the solar system followed this path from the molecular cloud from which the sun came. A minority originated bottom left along with the planets

A doctoral student claims to have solved the question of where the solar system's water comes from, including both our own oceans and the ice that makes up comets and the moons of the outer planets.

“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," says Dr Conel Alexander of the Carnegie Institution for Science. "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." 

Lead author Ilse Cleeves of the University of Michigan used the proportion of deuterium, an isotope of hydrogen with an extra neutron, to estimate water's source. Very cold environments, such as interstellar space, are more conducive to the formation of deuterium rich water than warmer environments around newly forming stars.

By simulating the proto-planetary conditions around the sun as it formed, Cleeves and Alexander concluded there is too much deuterium present for all of it to have formed along with the solar system. "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," said Cleeves.

In Science, Cleeves and Alexander estimate that 30-50% of the Earth's ocean has interstellar origins. In the outer reaches of the solar system the proportion is even higher, with 60 to 100% of comet ice being made in this way.

“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,” said Alexander.

Besides the astrobiological signicance, Cleeves told the discovery made her feel in touch with the cosmos. “For me, uncovering these kinds of direct links between our daily experience and the galaxy at large is fascinating and puts a wonderful perspective on our place in the universe." 


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