Earth's earliest water may have come from solar wind and space rocks

The interaction between the solar wind and the surface of asteroids may have created Earth's water

(Image credit: University of Glasgow)

Samples from asteroid Itokawa collected by a Japanese space probe suggest that Earth's water may have been created by the sun.

This water may have rained on the fledgling Earth in the form of dust grains produced by the interaction of the solar wind, the stream of charged particles emanating from the sun, with various bodies in the solar system, a new study suggests.

"The solar winds are streams of mostly hydrogen and helium ions which flow constantly from the sun out into space," Luke Daly, a planetary scientist at the University of Glasgow in the U.K., and a lead author of the new paper said in a statement. "When those hydrogen ions hit an airless surface like an asteroid or a spaceborne dust particle, they penetrate a few tens of nanometers [one inch has 24.5 million nanometers] below the surface, where they can affect the chemical composition of the rock."

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This mechanism may be the missing link explaining the abundance and chemical composition of water on Earth that has long baffled scientists. Earth's surface is 70% covered with water. That's much more than any other planet in the solar system. But none of the existing theories can fully explain all of it. A dominant view suggests that asteroids rich in carbon, which pummeled the young Earth some 4.6 billion years ago, delivered this water to the planet.

This discrepancy in what scientists call isotopic composition led researchers to believe that there must be at least one additional source of our planet's life-giving liquid. Isotopes are forms of chemical elements that differ just by the number of uncharged neutrons they contain. The carbonaceous chondrites tend to have water that contains more deuterium, a form of hydrogen with one neutron, while Earth's hydrogen is mostly a lighter form called protium that has no neutrons.

In search of the additional source of Earth's water, the team of researchers analyzed the composition of a rocky type of asteroid rich in silicon oxide using a novel technique called the atom probe tomography. Using this technique, the researchers measured the atomic structure of these grains one atom at a time to detect individual water molecules. The samples analyzed in this study came from the asteroid Itokawa, famously visited by the Japanese probe Hayabusa, which delivered tiny pieces of this space rock to Earth in 2010.

"[Our technique] lets us take an incredibly detailed look inside the first 50 nanometers [one inch has 24.5 million nanometers] or so of the surface of dust grains on Itokawa, which orbits the sun in 18-month cycles," Phil Bland, the director of the Space Science and Technology Center at Curtin University in Australia and co-author of the new study, said in the statement. "It allowed us to see that this fragment of space-weathered rim contained enough water that, if we scaled it up, would amount to about 20 liters [4.4 gallons] for every cubic meter [35 cubic feet] of rock."

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Tereza is a London-based science and technology journalist, video producer and health blogger. Originally from Prague, the Czech Republic, she spent the first seven years of her career working as a reporter, script-writer and presenter for various TV programmes of the Czech national TV station. She later took a career break to pursue further education and added a Master in Science from the International Space University, France, to her Bachelor's degree in Journalism from Prague's Charles University. She is passionate about nutrition, meditation and psychology, and sustainability.