The solar wind, comprised of solar particles largely made of hydrogen ions, created water on the surface of dust grains carried on asteroids that smashed into the early Earth, according to a paper published in the journal Nature Astronomy.
Daly et al. used atom probe tomography to directly observe an average ~1 mol% enrichment in water and hydroxyls in the solar-wind-irradiated rim of an olivine grain from the S-type asteroid Itokawa. Image credit: Curtin University.
“The Earth was very water-rich compared to other rocky planets in the Solar System, with oceans covering more than 70% of its surface, and scientists had long puzzled over the exact source of it all,” said Professor Phil Bland, director of the Space Science and Technology Centre at Curtin University.
“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.”
“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.”
Using atom probe tomography, Professor Bland and colleagues analyzed an olivine grain from the S-type near-Earth asteroid Itokawa, samples of which were collected by JAXA’s Hayabusa spacecraft and returned to Earth in 2010.
“Our world-class atom probe tomography system allowed us to take an incredibly detailed look inside the first 50 nm or so of the surface of Itokawa dust grains, which we found contained enough water that, if scaled up, would amount to about 20 liters for every m3 of rock,” Professor Bland said.
“It’s the kind of measurement that simply would not have been possible without this remarkable technology,” said Professor Michelle Thompson, a researcher in the Department of Earth, Atmospheric, and Planetary Sciences at Purdue University.
“It gives us an extraordinary insight into how tiny dust particles floating in space might help us balance the books on the isotopic composition of the Earth’s water, and give us new clues to help solve the mystery of its origins.”
“Our research not only gives scientists a remarkable insight into the past source of Earth’s water, but could also help future space missions,” said Dr. Luke Daly, a researcher in the School of Geographical and Earth Sciences at the University of Glasgow.
“How astronauts would get sufficient water, without carrying supplies, is one of the barriers of future space exploration.”
“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.”
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L. Daly et al. Solar wind contributions to Earth’s oceans. Nat Astron, published online November 29, 2021; doi: 10.1038/s41550-021-01487-w