The sun may have been the surprising source of Earth’s water

Where the Earth’s oceans that cover 70% of its surface came from remains a mystery, but now a team of international scientists has determined that the sun is likely a significant source of that water. Using atom probe tomography to analyse an ancient asteroid, they found that solar wind – the stream of mostly hydrogen and helium ions that flow from the sun – probably created water on the surface of dust grains brought to Earth on asteroids as the planet formed billions of years ago.

When hydrogen ions hit an airless surface like an asteroid or a spaceborne dust particle, they penetrate a few tens of nanometres below the surface and can affect the chemical composition of the rock. Over time, explained Luke Daly, a planetary scientist at the University of Glasgow and the paper’s lead author, this ‘space weathering’ effect can eject enough oxygen atoms from materials in the rock to create water.