Water on earth, moon came from same place
Traces of water inside the moon probably came from the same place as water on earth, a fresh analysis of lunar rocks has found.
The findings make for a clearer picture of our neighbour, once viewed as an arid expanse but now considered a frost-coated rock holding water throughout.
The results come from studies on the most extraordinary samples brought back from the moon, including green-tinged stone collected by Apollo 15 in 1971 and orange material gathered by Apollo 17 in 1972. Scientists focused on tiny droplets of volcanic glass that were trapped in crystals inside the rocks. The crystals protected the droplets from the violence of eruption, preserving in them a snapshot of the moon's ancient interior.
Evidence for water inside the glass droplets emerged in previous studies, but the latest US research goes further, showing that the lunar water is chemically identical to that on ancient earth.
According to the leading theory, the moon was created about 4.5 billion years ago from a hot cloud of debris that was knocked into space when a planet the size of Mars hit earth. The findings suggest earth was already damp at the time. "Some of that water survived the impact, and that's what we see in the moon," said Alberto Saal, a geologist at Brown University, Rhode Island.
To identify the source of the water, Saal and his colleagues relied on a chemical fingerprint, the relative amounts of hydrogen and deuterium, in the water.
They found the deuterium-hydrogen ratio in samples from the moon matched that of primitive asteroids called carbonaceous chondrites. The ratio is also similar to that found in water on earth. They said the fingerprint ruled out the possibility that the water on the moon rocks came from a comet, since comet water tended to have different deuterium-hydrogen ratios.
Additional reporting by Xinhua