Around 70% of Earth’s land surface is covered by water, though scientists have long puzzled over how this happened.
A team of international researchers has now suggested, using asteroid analysis, that the Sun might be the source of water for the Earth.
The researchers point to solar wind – a vicious stream of charged particles from the Sun largely made of hydrogen ions.
According to them, around 4.5 billion year ago, the solar wind produced water from grains of space dirt. These were then smashed into Earth in a spectacular meteor shower.

A artist’s impression depicting C-type asteroids & space dust falling down upon the Earth at an early stage of its formation. It was the space dust that carried water which created Earth’s oceans.

Itokawa Space Weathering Visualization: Artist’s impression showing the process of space weathering. This shows solar radiation and space dust on top of the Itokawa Asteroid.
The sun’s energy is still available today. It can reach speeds of 560 miles per seconds (900 km/sec) and maintain temperatures up to 2 million degrees Fahrenheit.
Space weathering was a method by which water from the dust grains became water during the creation of the Solar System. This process involved changing the chemical composition of grains so that water molecules could be produced.
‘The solar winds are streams of mostly hydrogen and helium ions which flow constantly from the Sun out into space,’ explains study author Dr Luke Daly at the University of Glasgow.
“When these hydrogen ions touch an airless surface, such as an Asteroid or a Spaceborne Dust particle, they penetrate several tens to nanometres under the surface. They can then affect the chemical structure of the rock.
‘Over time, the ‘space weathering’ effect of the hydrogen ions can eject enough oxygen atoms from materials in the rock to create H2O – water – trapped within minerals on the asteroid.’
Dr Daly thinks this process, and the resulting formation of oceans, happened before the formation of Earth’s magnetosphere – the area around Earth controlled by the planet’s magnetic field.

Artist’s impression showing the effects of solar radiation on dust particles in space.
MailOnline was told by he that there’s no consensus as to when Earth’s magnetic field formed.
“But the infall of small dust grains, large asteroids and that provided Earth’s water likely occurred within 5-15million years of the solar system’s history. Earth was receiving its last mass. This was probably long before the establishment of the magnetosphere.
Earth has a high water content compared with other rocky planets within the Solar System.
About 71 per cent of the Earth’s surface is water-covered, and Earth’s oceans hold about 96.5 per cent of all Earth’s water – but scientists had long puzzled over the exact source of it all.
An existing theory is that water was carried to Earth in the final stages of its formation 4.6 billion years ago on C-type asteroids – water-rich, primitive bodies in the asteroid belt.
‘However, previous testing of the isotopic “fingerprint” of these asteroids found they, on average, didn’t match with the water found on Earth meaning there was at least one other unaccounted for source,’ said study author Professor Phil Bland at Curtin University, Perth, Australia.
“Our research shows that water is created by the solar wind on tiny dust grains, which may have provided water for the remaining water in the earth’s surface.”
These new findings are the result of a careful atom-by atom analysis of tiny fragments from an S-type, near-Earth asteroid called Itokawa. It still orbits in outer space.
Itokawa samples were taken by Hayabusa, a Japanese space probe. They returned them to Earth in 2010.
Itokawa samples were examined using a sophisticated analytical method called Atom Probe Tomography.

This theory was based upon a detailed atom-by atom analysis of tiny fragments from an S-type near Earth asteroid called Itokawa. A scanning electron microscope image shows the Itokawa fragment.

Another image from the scanning electron microscope of the Itokawa segment. These fragments have a width similar to a human’s hair.
Atom probe photography allowed for the measurement of each atom in the grain’s atomic structure. It also enabled the detection and identification of individual water molecules.
Professor Bland explained that Curtin University’s world class atom probe imaging system allowed for an unprecedented look at the Itokawa dust grains’ surface in the 50-nanometer range.
The researchers found that water had been produced below the surface by Itokawa’s dust-sized grains through space weathering.
According to the research team, dust grains had enough water in them that they could hold approximately 20 litres of water per cubic meter of rock.

A scanning electron image showing a section of the Itokawa fragment that was made into a needle-like shape for Atom Probe Tomography Analysis
Researchers suggest that this water-rich dust could have fallen onto Earth as part of Earth’s delivery of oceans.
Dr Daly stressed the fact that space dust carrying ocean-forming water to Earth was not on asteroids. Rather, it was floating around in space and then raining down upon Earth early in the morning in the form a stunning shower.
They could have. space dust on the surfaces of asteroids that smashed into the Earth that would have brought water too – but only a small amount.
‘There is a lot more dust that is free floating in space at that time which, should enough of it fall onto the Earth would have a much bigger impact on Earth’s oceans,’ Dr Daly told MailOnline.

View of the Itokawa Asteroids’ water content. One of the Itokawa pieces was used for the study. The grey spheres are the grain’s surface, which has been protected with a layer of chromium. Blue spheres depict the distribution and concentration of water in one fragment of Itokawa. Image was taken using atom probe photography
The team claims that NASA’s Artemis Astronauts might be able, thanks to these new discoveries, to extract fresh water from lunar dust later in the decade.
Dr Daly explained that one barrier to future space exploration is how astronauts could get enough water without carrying any supplies.
Itokawa’s water was created by the same process of space weathering that occurred on other planets. This means that astronauts might be able extract fresh water from dusty planets like the Moon.
“NASA’s Artemis Project is aiming to create a permanent lunar base. It would be a valuable and enormous resource to help achieve this goal if the lunar surface had a comparable water reservoir, as discovered on Itokawa by solar wind.
This study was published in Nature Astronomy.

A SpaceX Starship illustration showing the human lander design for the SpaceX Starship. This will be used to transport first NASA astronauts to lunar surface in the Artemis program.