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Missing Zinc From Moon Rocks Suggest Moon's Origin, Local Scientists Find

A cross-polarized transmitted-light image of a polished section of Apollo sample 12021.
A cross-polarized transmitted-light image of a polished section of Apollo sample 12021.

Missing zinc from moon rocks could be evidence that the moon was created by a massive interplanetary collision soon after the formation of the solar system, scientists with the Scripps Institution of Oceanography announced today.

Zinc, which Scripps geochemist James Day and his partners call "a powerful tracer of the volatile histories of planets,'' is severely depleted on the moon, based on a comparison of moon rocks with those collected from Mars and the earth.

Similar elements, together called "volatiles,'' are also difficult to find in moon samples, they said in an article that will appear in Thurday's edition of the journal Nature.


"How do you remove all of the volatiles from a planet, or in this case a planetary body? You require some kind of wholesale melting event of the moon to provide the heat necessary to evaporate the zinc,'' Day said.

He said a gigantic collision could have eradicated the elements from the moon as it was created, while also providing the earth with rare metals like gold and platinum.

Day, along with Randal Paniello and Frederic Moynier of Washington University in St. Louis, used a mass spectrometer device, which measures the ratios of isotopes of chemical elements. He said information was revealed that was not available even five years ago.

In their article, they wrote that the large-scale evaporation of zinc must have come about "most likely in the aftermath of the moon-forming event, rather than small-scale processes during volcanic processes.''

He said the moon rocks were collected during the Apollo missions 40 years ago.


"They still have a lot of science to be done on them and that's exciting,'' said Day. "Hopefully these kinds of results will help push for future sample collection missions to try to more fully understand the moon.''

He said his findings will lead him toward investigating why the Earth is mostly covered by water.

The research was funded by the NASA Lunar Advanced Science and Exploration Research and Cosmochemistry programs.