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Space dust study could explain how water originated on Earth

By Adam Schrader
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Space dust study could explain how water originated on Earth
An artist’s impression of C-type asteroids and space dust raining down on the Earth early in its formation, carrying with them some of the water that formed the Earth’s oceans. Photo courtesy of University of Glasgow

Nov. 29 (UPI) -- A new analysis of space dust shows that the water covering the majority of Earth's surface could have formed in space with help from solar wind.

An international team of researchers studied samples taken from the asteroid Itokawa by the Japanese space probe Hayabusa in 2010, according to a paper published Monday in the journal Nature Astronomy.

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The scientists used a process called atom probe tomography to measure the atomic structure of individual grains of dust on the asteroid and detect water molecules.

The water molecules found on Itokawa were formed when hydrogen ions flowing from the sun collided with dust particles on the space rock -- changing their chemical composition, according to Luke Daly of the University of Glasgow's School of Geographical and Earth Sciences.

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"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," Daly, the study's lead author, said in a press release.

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The study could be key to explaining a decades-old theory among scientists that asteroids brought water to Earth when the planet was formed around 4.6 billion years ago.

Previous studies have found that the chemical composition of water on water-rich meteorites from C-Type asteroids did not match that of Earth's water.

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Daly noted that the water molecules found on Itokawa more similarly match the isotopic makeup of the water on Earth. Itokawa is an S-Type asteroid, which orbits closer to the sun than C-Type asteroids.

"That strongly suggests that fine-grained dust, buffeted by the solar wind and drawn into the forming Earth billions of years ago, could be the source of the missing reservoir of the planet's water," Daly said.

Co-author Phil Bland, a distinguished professor at Curtin University, explained that the atom probe tomography method allowed the scientists to discover enough water on Itokawa that "it would amount to 20 liters of water for every cubic meter of rock." This would demonstrate that a significant amount of water could have been carried to Earth as the planet formed.

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The study concludes that "the contribution of solar-wind-derived water may not be limited to delivery from fine-grained dust." Before a proto-planet becomes a planet, it exists in a debris disk stage as a collection of dust and space rock in orbit around a star. The researchers noted that all materials "will experience a radiation-rich environment" during the debris disk stage.

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"Thus, all dust produced during this period will incorporate solar-wind-derived water," the study reads.

Daly explained that scientists were able to determine that the water molecules were formed in space by comparing them to samples irradiated with helium and deuterium instead of hydrogen that were provided by NASA and other collegiate institutions.

"NASA's Artemis project is setting out to establish a permanent base on the moon. If the lunar surface has a similar water reservoir sourced by the solar wind this research uncovered on Itokawa, it would represent an enormous and valuable resource to aid in achieving that goal," Daly said.

Hope Ishii, a professor at the University of Hawaii at Mānoawho who co-authored the paper, said in the release that it is "reasonable to assume" that water has formed on other asteroids in space through the process of space weathering -which could prove crucial to future space exploration.

"Space explorers may well be able to process fresh supplies of water straight from the dust on the planet's surface," she said. "It's exciting to think that the processes which formed the planets could help to support human life as we reach out beyond Earth."

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