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Water Discovered on the MoonIs the Moon the result of a massive impact? |
By Gabriel Gache, Science News Editor
10th of July 2008, 07:18 GMT
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Soil samples returned from the Moon during the Apollo missions were for the first time proven to contain trace amounts of water, although they cannot indicate how much water is currently present there nor can they be used to predict a method through which water could be extracted in the near future. The long expected discovery was made during the analysis of volcanic glass beads brought back from the Moon and may have significant importance regarding the past of Earth's satellite, especially in terms of the process that created it.
"This really appears to have changed the rules of the game. The assumption has been that the moon is dry," said Robin Canup, astrophysicist and director of the Southwest Research Institute in Boulder, who did not participate in the study.
It is widely believed that the Moon was formed some 4.5 billion years ago when a planet roughly the size of Mars collided with Earth. The tremendous impact tore molten pieces out of Earth which eventually were shaped by gravity into the large Moon we see today. In fact, Earth has the biggest Moon in the solar system in relation to its size. However, this Moon formation theory implies that during its formation all of the water would be vaporized and lost into space, making the satellite extremely dry.
"If there was a lot of water in the early moon, then that is new for sure. People will have to think about that when they think about how the moon evolved," said Ben Bussey, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
Nonetheless, regardless of the implications of the process that led to the creation of the Moon, researchers have been trying for more than four decades to determine if the Moon could hold some amounts of water on its surface. "I thought that if we were really lucky we would get to see it. Like everybody else, I was thinking our chances were low," said leader of the study Alberto Saal, a geochemist at Brown University.
Saal's research team found that the glass beads contained in the samples returned back to Earth during the Apollo missions are most likely drops of molten lava coming from deep within the Moon's inner regions, not from the impact that created the Moon. Additionally, there is little evidence that the samples could have been contaminated with hydrogen gas carried out by the solar wind.
"For the past four decades, the limit for detecting water in lunar samples was about 50 parts per million (ppm) at best. We developed a way to detect as little as 5 ppm of water," said co-author of the study Erik Hauri, geochemist at the Carnegie Institution in Washington.
The secondary ion mass spectrometry technique the team used in studying the beads revealed an amount of 46 ppm of water inside the volcanic glass droplets, indicating that they may actually hold up to 745 ppm of water, close to the water contents of solidified lava originating in the upper mantle of the planet. However, the team calculated that the true concentration of water is most likely somewhere around 260 ppm.
The fact that the Moon contains any water at all raises several questions to how it came to exist in the first place or if the current model is correct, as well as how it would be possible for the Moon to retain water or gather it in its first 100 million years, before the surface solidified. The models also predict that Earth lost little water during the Moon formation process, albeit they cannot say much about the water content of the Moon.
"The major uncertainty I see is whether they're sampling something that tells us about the bulk composition of the moon, or whether they have sampled materials produced by a more limited water-rich part of the moon's interior," Canup said.
Knowing exactly how much water is present on the Moon can have significant consequences on the future of lunar exploration, but would have little effect on the currently scheduled missions, such as the Lunar Reconnaissance Orbiter or the Lunar Crater Observation and Sensing Satellite, which is set to find evidence of water on the Moon's poles by impacting two spacecrafts into its surface.
If indeed the surface contains water ice, it most likely came from other bodies in the solar system, although some amounts could be remnant from the Moon's violent birth. Further analysis of samples returned by the Apollo missions may partially answer some of the questions raised by the new discovery, and could seal the faith of future lunar exploration. "I think it's exciting that you keep getting results out of the Apollo samples," Bussey said.
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