Water, Water Everywhere… but Why?

Water molecules found in meteorites from asteroids like Itokawa have matching isotopes to water molecules found on Earth but not water-rich meteorites.

IMAGE: Meteorites on their way to Earth and breaking through the atmosphere. CREDIT: Elements of this image furnished by NASA- earthmap for 3Drender; courtesy University of Glasgow

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…