Lunar Sample Studies Point to Meteorites as Common Earth, Moon Water Source


New evidence gathered from studies of lunar magma samples collected by the Apollo 15 and 17 mission astronauts suggest the moon and Earth share a common primary source of water, the carbonaceous chrondrite meteorites from the region of the asteroid belt rather than colliding comets that originated in the more distant regions of the solar system.

Earth, moon share meteorites as water source. Photo Credit: NASA

The findings suggest that water on the Earth survived the tremendous heat generated by the impact from a large planetary body 4.5 billion years ago. The collision cleaved off material from the Earth that coalesced from a debris disc into the moon and terrestrial water that became locked within the lunar mantle.

The research carried out by scientists from Brown University, the Carnegie Institution of Washington and Case Western Reserve University builds on observations from NASA's 2011-12 Gravity Recovery and Interior Laboratory (GRAIL) mission that suggest the moon began with a thick hotter outer shell and much colder interior. The latest findings, Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chrondrite Heritage, appear in May 9-10 editions of the  journal Science and Science Express.

Earlier assumptions of lunar formation suggested that heat from the impact would have led to the boil off of volatiles, including hydrogen.

"The simplest explanation for what we found is that there was water on the proto-Earth at the time of the giant impact," said Alberto Saal, an associate professor of geological sciences at Brown and the study's lead author, in a statement. "Some of that water survived the impact, and that's what we see in the moon."

The interpretation is based on studies of volcanic glass particles trapped within olivine crystals in the volcanic samples from the Apollo 15 and 17 lunar missions of 1971 and 1972. The tiny particles were examined with a Cameca NanoSIMS 50L multicollector ion microprobe.

Previous studies found water in the lunar glass particles in quantities rivaling similar particles found in lavas that form on the Earth's ocean floor. Saal and his colleagues traced the origins of the lunar water by examining the ratio of the deuterium isotope to hydrogen in the glass samples.

The relatively low ratio provided a "fingerprint" that matched the deuterium/hydrogen ratio found on Earth as well as in the carbonaceous chondrites. Comets, long thought to be the source of ice locked in permanently shaded regions of craters at the moon's poles, display a higher ratio.

"The new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and moon, and perhaps the entire inner solar system," said co-author and Carnegie Institution geochemist Erik Hauri in a statement.

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