The sun's solar wind may have played a role in bringing water to Earth, resolving a long-standing mystery about the origins of our planet's seas and oceans.

A new study suggests that Earth's 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, according to samples collected by a Japanese space probe from asteroid Itokawa.

"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."

Solar wind is primarily made up of hydrogen ions emitted by the sun, which react with oxygen atoms in asteroid rock to form water. Previous research has shown that asteroids like Itokawa can hold a lot of water, but it's unclear where that water came from.

Our solar system is believed to have been densely populated with dust in its early stages, so some of it may have been converted to water by the solar wind before being carried down to Earth's surface after its formation. This water, crucially, contains less deuterium than asteroids deliver.

"You could produce Earth's oceans by mixing those two reservoirs together," Daly said.

This mechanism could be the missing link in the puzzle of water's abundance and chemical makeup on Earth, which has long perplexed scientists. 70% of the Earth's surface is covered in water. This is far more than any other planet in our solar system. However, none of the known theories can completely explain everything. According to popular belief, water was supplied to the globe by carbon-rich asteroids that slammed into the infant Earth 4.6 billion years ago.

However, a careful chemical analysis of carbonaceous chondrites, which are fragments of these carbon-rich asteroids, discovered that the water contained within them does not match the chemical fingerprint of Earth's water.

This difference in isotopic makeup prompted scientists to think that our planet's life-giving liquid must come from at least one additional source.

The research is described in a paper published Monday in the journal Nature Astronomy.