Solar Wind A Source of Earth’s Water

The source of the Earth’s water has long been theorised to have been C-type asteroids, which brought water to the Earth during its final stages of formation. C-type asteroids make up around 75% of asteroids and are distinguished by their high carbon content. According to this theory, the Earth was dry during its initial formation and water was carried and brought to the Earth’s surface through collisions with C-type asteroids. 

However, scientists, in a newly published paper have found that the isotopic “fingerprint” of the Earth’s water doesn’t completely match this theory. Instead, these scientists propose, and present findings that suggest, that solar wind from the Sun is a previously unaccounted source of Earth’s water.  

This new paper comes from a University of Glasgow-led international team of researchers, including researchers from Curtin University’s Space Science and Technology Centre (SSTC). Curtin’s world-class atom probe tomography system played a key role in analysing samples of an S-type (silicon dioxide-based) asteroid. Most of these asteroids are located in the inner asteroid belt, within 2.2 AU from the Sun. Looking at this type of asteroid has helped researchers explore how Earth came to have water on its surface.

“An existing theory is that water was carried to Earth in the final stages of its formation on C-type asteroids, 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,” SSTC Director, John Curtin Distinguished Professor Phil Bland said.

“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.

“This new solar wind theory is based on meticulous atom-by-atom analysis of minuscule fragments of an S-type near-Earth asteroid known as Itokawa, samples of which were collected by the Japanese space probe Hayabusa and returned to Earth in 2010.

“Our world-class atom probe tomography system here at Curtin University allowed us to take an incredibly detailed look inside the first 50 nanometres or so of the surface of Itokawa dust grains, which we found contained enough water that, if scaled up, would amount to about 20 litres for every cubic metre of rock.” 

Using this data, researchers have found that solar wind created water on the surface of dust grains carried on asteroids that smashed into the Earth during the early days of the Solar system. The solar wind is a stream of charged particles released from the upper atmosphere of the Sun (the Solar Corona), which is mostly made up of hydrogen ions. 

Curtin graduate Dr Luke Daly, now of the University of Glasgow and lead author of this new research paper said that these findings could be useful for future space missions.

“How astronauts would get sufficient water, without carrying supplies, is one of the barriers of future space exploration,” Dr Daly said.

“Our research shows that the same space weathering process which created water on Itokawa likely occurred on other airless planets, meaning astronauts may be able to process fresh supplies of water straight from the dust on a planet’s surface, such as the Moon.”