Scientists edge closer to understanding how water arrived on planet Earth

Water trapped in asteroids could be the source of the Earth's seas

Scientists at Brown University in the US have got one step closer to discovering how water arrived on planet Earth.

Through experiments using a high-powered projectile cannon, the research was able to show how impacts by water-rich asteroids could be able to deliver large volumes of water to planetary bodies.

The research is also said to help account for some trace water detections on the Moon and elsewhere.

"The origin and transportation of water and volatiles is one of the big questions in planetary science," said the study's post-doctoral researcher at Johns Hopkins University, Terik Daly, who led the research while completing his PhD at Brown University, Rhode Island.

"These experiments reveal a mechanism by which asteroids could deliver water to moons, planets and other asteroids. It's a process that started while the solar system was forming and continues to operate today."

Until now, the source of Earth's water has remained a mystery. It was long thought that the planets of the inner solar system formed bone dry and that water was delivered later by icy comet impacts.

These experiments reveal a mechanism by which asteroids could deliver water to moons, planets and other asteroids

While that idea remains a possibility, new isotopic measurements have shown that Earth's water is similar to water bound up in carbonaceous asteroids, suggesting that asteroids could also have been a source for Earth's water, but how such a delivery mechanism might have worked isn't well understood.

"Impact models tell us that impactors should completely devolatilise at many of the impact speeds common in the solar system, meaning all the water they contain just boils off in the heat of the impact," said Pete Schultz, co-author of the paper. "But nature has a tendency to be more interesting than our models, which is why we need to do experiments."

For the study, Daly and Schultz used marble-sized projectiles with a composition similar to carbonaceous chondrites, meteorites derived from ancient water-rich asteroids.

Using the Vertical Gun Range at the NASA Ames Research Center, the projectiles were blasted at a bone-dry target material made of pumice powder at speeds of around five kilometres per second. They then analysed the post-impact debris with an armada of analytical tools, looking for signs of any water trapped within it.

They found that at impact speeds and angles common throughout the solar system, as much as 30 per cent of the water indigenous in the impactor was trapped in post-impact debris.

The findings could have significant implications for understanding the presence of water on Earth.

"The point is that this gives us a mechanism for how water can stick around after these asteroid impacts," added Schultz. "And it shows why experiments are so important because this is something that models have missed."