Where did the waters of the Earth originate? Astronomers have theorized for a few years that asteroids and comets deposited water on the Earth's surface during the early days of our planet, but there are still many questions.

Now, according to a report published in Nature Astronomy, the Sun might have been an additional source, with solar winds combining with minerals in space dust to generate water molecules.

Samples from Japan's Hayabusa spacecraft mission, which delivered a piece of an asteroid to Earth in 2010, were examined by an international team of experts.

“We started off wanting to measure the effects of space weathering on the particles that were brought back from this asteroid,” says co-author Associate Professor Nick Timms, from Curtin University.

The 'isotope composition' of hydrogen (the ratio of heavier to lighter hydrogen atoms) in the sample near the surface, however, was not what the researchers expected.

The solar wind, which distributes protons, which are the same as hydrogen (H+) ions, was found to have thrown off the ratio.

“It’s only the surfaces of the particles in this asteroid that have been exposed to the Sun that have this implanted layer of hydrogen,” says Timms.

The researchers believe that by adding another source of hydrogen to the equation, they can better understand the isotopic makeup of the Earth's seas. The solar wind's hydrogen ions (H+) interacted with oxygen atoms (O) in silicates in the rock to form water (H2O).

"An existing theory is that water was carried to Earth in the final stages of its formation on C-type asteroids," says co-author Professor Phil Bland, also of Curtin. "However, the previous testing of the isotopic 'fingerprint' of these asteroids found they, on average, didn't match the water found on Earth, implying there was at least one other unaccounted for source."

“Our research suggests the solar wind created water on the surface of tiny dust grains and this isotopically lighter water likely provided the remainder of the Earth’s water.”

According to Timms, the finding has fascinating implications for space exploration.