Researchers have pinpointed how solar wind—a stream of charged particles from the Sun—triggers water molecule formation on dust grains from asteroids that impacted the early Earth.
Earth stands out among rocky planets for its abundant water, sparking decades of debate on its origins. One leading hypothesis points to water delivery via C-type asteroids during Earth's final formation stages. Yet, isotopic analyses of these asteroids reveal mismatches with Earth's water, indicating another source.
In a study published in Nature, experts from Curtin University in Australia and the University of Glasgow in Scotland identified this missing "isotopic reservoir." Their findings show that solar wind, rich in hydrogen ions, enables water formation on tiny dust grains carried by S-type asteroids.
The breakthrough stems from atomic analysis of Itokawa fragments—an S-type asteroid—collected by Japan's Hayabusa probe in 2005 and returned to Earth in 2010.
"Our world-class atom probe tomography enabled us to examine the top 50 nanometers of Itokawa dust grains in exquisite detail," says co-author Dr. Phil Bland. Extrapolating their data, the team estimates each cubic meter of such material contains about 20 liters of water.
This research illuminates a key pathway for Earth's water delivery and holds promise for space exploration.
"Sourcing water without hauling supplies is a major hurdle for astronauts," notes co-author Dr. Daly. "Our findings suggest that solar wind-driven processes on other airless bodies could yield extractable water from surface dust."
