May 29, 2014
Distribution Of Lunar Water Sheds Light On Complexities Of Moon Formation
redOrbit Staff & Wire Reports - Your Universe Online
By reviewing hundreds of chemical analyses of lunar samples collected during the Apollo missions, scientists have discovered new clues about how water originated and was redistributed on the Moon, according to a recently published Nature Geoscience paper.
In their study, lead author Katharine Robinson of the University of Hawai'i – Mānoa (UHM) School of Ocean and Earth Science and Technology and her colleagues explained that the initial analysis of the Apollo samples indicated that the moon was anhydrous, or completely devoid of water. Now, however, improved analytical techniques have proven that pyroclastic glass beads included in those samples actually contain a measurable quantity of water.
The water found in those beads is not liquid H2O, but water contained in volcanic glasses or chemically bound in mineral grains contained inside lunar rocks, the study authors reported. Rocks originating from some locations in the moon’s interior were found to contain far more water than rocks obtained elsewhere, and the hydrogen isotopic composition of lunar water varied from region to region as well, they added.
“The present consensus is that the Moon formed as the result of a giant impact of an approximately Mars-sized planetesimal with the proto-Earth,” the university said. “The water in the Moon is a tracer of the processes that operated in the hot, partly silicate gas, partly magma disk surrounding Earth after that impact.”
The source of the moon’s water and the source of Earth’s water are linked, according to Robinson’s team. It is possible that the moon inherited water from the Earth during the impact that formed our planet’s natural satellite. Conversely, it could have been added to the moon later by comets or asteroids, or it could be a combination of both. Either way, Robinson said that it appears that whatever happened to the moon also happened to the Earth.
The UHM research team compiled water measurements from lunar samples that had been taken from scientists throughout the world, as well as some of their own. They focused specifically on hydrogen and its isotope deuterium, which includes an extra neutron in its nucleus, measuring each using microprobes that used a focused beam to sputter a small rock sample’s ions into a mass spectrometer.
By determining the ratio of hydrogen to deuterium, they were able to pinpoint the source of the water or trace magmatic processes in the lunar interior. Their findings, Robinson said, are “surprising” because they demonstrate that “lunar formation and accretion were more complex than previously thought.”
“Studies of water in the lunar interior are just beginning, and it is clear that more data are needed,” the authors concluded. “The important point is that water concentration and hydrogen isotopic composition vary inside the Moon, and these variations might be useful tracers of lunar formation, differentiation and early bombardment.”
Image 2 (below): This shows secondary electron image of pits left by ion microprobe analyses of a heterogeneous apatite grain in Apollo sample 14321, 1047. Water has now been detected in apatite in many different lunar rock types. Credit: Katharine L. Robinson, University of Hawaii, HIGP