spacetoday.net: Water on Earth and in Moon may come from same source

Posted: Fri, May 10, 2013, 7:56 AM ET (1156 GMT)
Water in the Moon's interior has the same isotopic ratios as water on the Earth, indicating that the Moon's water may have come from the Earth when it formed. Scientists measured the ratio of deuterium to hydrogen in water trapped in volcanic rocks returned by the Apollo missions and found that the ratio is similar to that found in water on Earth, but lower than that seen in comets. The researchers conclude that the water trapped in the Moon came from the Earth when a protoplanet collided with the early Earth, creating the Moon, rather than from impacts of comets after the Moon formed. That formation process was previously thought to have vaporized any water. Other scientists, though, argue that the lunar rocks sampled in this study are outliers and may not be representative of the Mon's composition in general.