Water discovery challenges "giant impact" theory of the Moon's formation

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Washington, July 10 : Scientists have discovered for the first time that tiny beads of volcanic glasses collected from two Apollo missions to the moon contain water, which suggests 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.

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 forty years, there have been significant efforts to determine the content and origin of the volatile contents 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 water 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 University, took advantage of new methods for analyzing lunar samples to detect tiny amounts of water.

Co-author of the paper, 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).

"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 5 ppm of water. We were really surprised to find a great deal more in these tiny glass beads, up to 46 ppm," he added.

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," said Hauri. "It suggests the intriguing possibility that the Moon's interior might have had as much water as the Earth's upper mantle," he added.

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