Asteroids release half of the Earth's water, suggests a new sample

The water of a grain of dust

Researchers Ziliang Jin and Maitrayee Bose received only five grains of Hayabusa, each covering half the width of a human hair. Two of these five particles contained the mineral pyroxene, which often contains water on Earth. They used an instrument called a mass spectrometer to determine the amount of water in the Itokawa pyroxene.

What they found was surprised. The Itokawa grains were not only rich in water, but the chemistry of this water was very close to that of the Earth. They published their findings on May 1 in the journal Progress of science.

For decades, scientists have wondered where the Earth has all its water. Did the Earth form with its water, or was it later delivered by a cosmic hail storm of comets or asteroids? If yes which? The evidence has changed over the years. Much of the uncertainty comes from the fact that scientists have very few physical samples to study.

And all the waters are not equal. Most waters contain one atom of oxygen and two atoms of hydrogen: H2O. But some waters contain deuterium instead of conventional hydrogen. It is a heavier version of hydrogen with an extra neutron in the center. When scientists find the water source of the Earth, they expect it to match the fraction of deuterium they observe in the Earth's oceans. But it's hard to measure that, without physical samples like Itokawa's.