Meteorites are useful for answering all kinds of questions, including why is there so much water on Earth? One theory that has been gaining steam, so to speak, is that some of the liquid water we have on Earth comes from water-rich meteorites. But the isotopes didn’t always match, particularly when it comes to water in the mantle and oceans. So perhaps some of our water is a result of our planet being bombarded by dust grains that came from asteroids and comets, where those dust grains contained water. And upon analyzing a different type of asteroid than the ones that give us those water-rich meteorites, including Itokawa which was sampled by JAXA’s Hayabusa probe, they found water molecules that isotopically matched what we were missing.

As scientists have worked to understand this process, a question remained about just how the water got into the dust grains. In a new paper in Nature Astronomy, a team lead by Luke Daly has concluded that the water came from space weathering, where charged particles from the Sun traveled through the solar system via the solar wind and altered the chemical composition of the original dust grains so that they now contained water.

Daly explains further: 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. Crucially, this solar wind-derived water produced by the early solar system is isotopically light. 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.

In simple terms: the solar wind is producing water under the surface of asteroids, and that water made it to Earth. Co-author John Bradley notes: Since much of the dust throughout the solar nebula was inevitably irradiated prior to its accretion into larger objects, water produced by this mechanism is highly relevant to the origin of water in planetary systems and possibly the isotopic composition of Earth’s oceans.”

And maybe we could use dust on other worlds like Ceres or Vesta or even the Moon to process water straight from the surface. That’s an interesting idea for in situ resource utilization, I think.

More Information

University of Hawai‘i at Mānoa press release

“Solar wind contributions to Earth’s oceans,” Luke Daly et al., 2021 November 29, Nature Astronomy