Greenwood Debates the Source of Water on the Moon

In a story for PBS Newshour, James Greenwood, research associate professor of earth and environmental sciences, disputes a newly published finding by other scientists that water on the moon originated on the planet Earth, and was transferred during a massive collision 4.5 billion years ago. Comparing the specific proportions of hydrogen isotopes to deuterium isotopes in water found on the moon and the Earth, Greenwood argues that it’s not a close enough match to conclusively proof that the water on the moon is terrestrial. Instead, he maintains that the water arrived later, and probably from a comet.

“They are arguing that they have the same source of water and the source survived the impact event without changing the isotope signature,” Greenwood said. “It’s still similar to cometary water.”

And given the isotopic ranges we currently have for comets, they’re pretty close to Earth’s water, he added. “If comets have a deuterium to hydrogen ratio the same as the Earth’s oceans, then comets could have delivered all the water.”

Greenwood is also visiting assistant professor of earth & environmental sciences and interim faculty director of the McNair Program.