Scientists believe Earth’s abundant H2O was supplied by space rocks that slammed into the planet during its infancy 4.6 billion years ago.

But the isotope-ratio fingerprint of Earth's ocean water only partly matches the pattern found in meteorites. So where did the rest of the water come from?

New research published in the journal Nature Astronomy offers a possible solution: weathering of silicate space rocks by charged particles from the sun.

"You can actually detect the water on the asteroid that presumably wasn't originally there. But it formed from the solar wind hitting the surface — the hydrogen hitting the surface — reacting and making water," said coauthor and NAU astronomer Mark Loeffler.

On Earth, one molecule of water in 10,000 is made of deuterium — hydrogen with a neutron in its nucleus.

That "heavy water" ratio varies throughout the solar system, including in the carbon-rich meteorites thought to be Earth's main water-bearers. 

But, surprisingly, supposedly dry silicate asteroids can make water, too, when charged hydrogen atoms from solar wind combine with oxygen atoms in their surface rock.

"You can make water from the hydrogen implanting into this surface, which has a lot of oxygen in it in the form of some rocky material, or silicates," said Loeffler, who helped test the hypothesis. 

Adding water from silicate meteorites and dust grains could offset the heavier isotope ratio of water from carbon meteorites, resulting in a cocktail that matches isotope fingerprint of Earth's oceans.

The findings were based on studies of an asteroid sample from the silicate asteroid Itokawa, returned to Earth by the Japanese Hayabusa space probe mission a decade ago. 

"This is the first detection of water in any asteroid material that's been returned from space," said Loeffler.

More Stories From KJZZ

• Arizona Scientists Will Soon Analyze JAXA Asteroid Sample
  
• Asteroid Sample Helps Settle Which Scientific Theories Hold Water