Water From A Grain of Dust
Researchers Ziliang Jin and Maitrayee Bose got just five grains from Hayabusa, each spanning a mere half the width of a human hair. Two of those five particles contained the mineral pyroxene, which on Earth often contains water. So, the pair used an instrument called a mass spectrometer to see how much water there was in Itokawa’s pyroxene.
What they found surprised them. Not only were Itokawa’s grains rich in water, but the chemistry of that water very closely matches the water on Earth. They published their results May 1 in the journal Science Advances.
For decades, scientists have wondered where Earth got all its water. Did Earth form with its water baked in, or was it delivered later by a cosmic hailstorm of comets or asteroids? If so, which? The evidence has tipped back and forth over the years. Much of the uncertainty is because scientists have very few physical samples to study.
And not all water is created equal. Most water contains one atom of oxygen and two atoms of hydrogen: H2O. But some water contains deuterium instead of conventional hydrogen. It’s a heavier version of hydrogen that has an extra neutron at the center. When scientists find the source of Earth’s water, they expect it will match the fraction of deuterium that scientists observe in Earth’s oceans today. But measuring that is tricky to do without physical samples like those from Itokawa.