A research team including Jim Van Orman, a Case Western Reserve University faculty member, has uncovered that, contrary to accepted theory, there may be water within the Moon's interior.
Using new techniques, scientists from three major research universities have discovered for the first time that tiny beads of volcanic glasses collected from two Apollo missions to the Moon contain water.
Jim Van Orman, associate professor of experimental petrology and geochemistry in the geological sciences department at Case Western Reserve University, and the other researchers found that water was not entirely vaporized in the violent events that formed the Moon. The new study suggests that the water came from the Moon's interior and was delivered to the surface via volcanic eruptions over 3 billion years ago.
The finding calls into question some critical aspects of the "giant impact" theory of the Moon's formation and may have implications for the origin of possible water reservoirs at the Moon's poles. The research is published in the current issue of Nature.
Water found within the Moon's surface could have a big effect on any future plans for long-term manned lunar presence or using the Moon as a launching point for explorations further into space, said Van Orman. "Water contains the essential ingredients used for rocket fuel," he said. "Certainly, if there is ice on the Moon's polar caps, that could be used. But if there is water in the rocks -- and as much as our studies infer -- that is another resource that could be tapped."
It is believed that the Moon was formed when a Mars-size body collided with Earth some 4.5 billion years ago. This "giant impact" melted both objects and sent molten debris into orbit around the Earth, some of which coalesced to form the Moon. Under this scenario, the heat from the giant impact would have vaporized the light elements.
Over the past 40 years there have been significant efforts to determine the content and origin of the volatile contents -- such as water -- in the lunar samples. There is reliable evidence that the Moon's interior contains sulfur, some chlorine, fluorine and carbon. Yet the evidence for indigenous H2O has remained elusive, consistent with the general consensus that the Moon is dry.
The research team, with scientists from Brown University, Carnegie Institution for Science and Case Western Reserve, took advantage of new methods for analyzing lunar samples to detect tiny amounts of water.
The paper's co-author Erik Hauri of the Carnegie's department of terrestrial magnetism developed new techniques that can detect extremely minute quantities of water in glasses and minerals by the technology called secondary ion mass spectrometry (SIMS). These technical advances were made in collaboration with engineers from Cameca Instruments (France), who manufactured the NanoSIMS instrument used to make these challenging measurements.
"For the past four decades, the limit for detecting water in lunar samples was about 50 parts per million (ppm) at best," explained Hauri. "We developed a way to detect as little as five ppm of water. We were really surprised to find a great deal more in these tiny glass beads, up to 46 ppm."
One glass bead told the tale of what happened. The researchers found that the volatiles decreased from the tiny sphere's core to its rim – a difference that indicates that some 95 percent of the water was lost during the volcanic activity.
Van Orman wrote the numerical model that brought about this conclusion. He became involved in the lunar project at a chance meeting with Hauri and Alberto Saal of Brown University – with whom he had collaborated before – at a conference in Germany.
They told Van Orman of their project and of their dissatisfaction with the numerical models they were using to determine the presence and loss of volatiles during the creation of the glass beads. He mentioned that he had confronted a similar problem in his lab work on experimental diffusion profiles.
Invited to join the project, Van Orman was on a fast track to run through thousands of models to come up with the parameters that best fit the measured volatile contents in the lunar glass beads.
"We looked at many factors over a wide range of cooling rates that would affect all the volatiles simultaneously and came up with the right mix," he said.
"A droplet cooling at a rate of about three degrees Fahrenheit to six degrees Fahrenheit per second over a time frame of two to five minutes between the time of eruption and when the material was quenched, or rapidly cooled, matched the profiles of all the volatiles, including the loss of about 95 percent of the water," he said.
The researchers estimated that there was originally about 750 ppm of water in the magma at the time of eruption. "Since the Moon was thought to be perfectly dehydrated, this is a giant leap from previous estimates," continued Hauri.
"It suggests the intriguing possibility that the Moon's interior might have had as much water as the Earth's upper mantle," he said. "But even more intriguing: If the Moon's volcanoes released 95 percent of their water, where did all that water go?"
Since the Moon's gravity is too feeble to retain an atmosphere, the researchers speculate that some of the water vapor from the eruptions was probably forced into space, but some may also have drifted toward the cold poles of the Moon where ice may be present in permanently shadowed craters.
Several previous lunar missions have suggested the presence of ice at both poles. Unless it is very deep, lunar groundwater is unlikely to exist since the sun heats most of the Moon's surface to over 200 degrees Fahrenheit (100 degrees Fahrenheit).
Van Orman and the other team members came to the lunar project previously having devoted their individual research efforts to conditions here on Earth. Because they had focused on terrestrial matters prior to this project, the team members brought a fresh approach to the issue of water on the Moon.
Among Van Orman's research interests are understanding processes of chemical differentiation in the Earth, Moon and meteorite parent bodies and the rheology of Earth's lower mantle and inner core. Like others on the research team, much of Van Orman's previous work looked at conditions here on Earth and was not devoted specifically to lunar studies.
Lead author Alberto Saal of Brown University remarked: "Beyond the evidence for the presence of water in the interior of the Moon, which I found extremely exciting, I learned that the contributions from scientists in other disciplines have the potential to produce unexpected results. Such a scientist is able not only to ask questions that no one has asked before, but also can challenge hypotheses that are embedded in the thinking of the scientists working in the field for many years. Our case is a typical example. When I suggested we measure volatiles in lunar material, everyone I talked to thought that such a proposal was a futile endeavor. We 'knew' the Moon was dry."
Many scientists have believed the Moon's polar ice, if there, originated from impacts of water-rich meteoroids and comets that struck the Moon's surface over its history. The new study suggests that some of this water could have come from lunar volcanic eruptions. Verifying that water is at the Moon's poles is one goal of the NASA Lunar Reconnaissance Orbiter mission, due to launch later this year. And it is the primary objective of the Lunar Crater Observation and Sensing Satellite with a 2009 launch date.
Funding for the study came from the Carnegie Institution for Science and NASA.
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