New Moon

This photograph of the full Moon was taken from Apollo 11 during its trip back to Earth from a distance of roughly 18,000 km. Courtesy of NASA

Friday, December 21st, 2007--

The moon might not be as old as scientists thought--it may be thirty million years younger, according to a new study in the journal Nature. Mathieu Touboul of the Swiss Federal Institute of Technology in Zurich, Switzerland and his colleagues analyzed the elements in moon specimens to determine the moon's age.

Using a technique called radiometric dating, the researchers estimated the age of the moon by measuring the presence of the isotope tungsten-182, in relation to hafnium-182. Hafnium-182 radioactively decays into tungsten-182 with a half-life of 9 million years.

But using tungsten to date the moon can be complicated by the fact that tungsten-182 is also produced by another element. In past studies, the other production of tungsten had to be corrected for. In this study, the researchers figured out a way to isolate tungsten produced only by hafnium--allowing for more accurate dating.

The new data challenges not only the assumption about the moon's age, but also how the moon was formed. Current computer models predict that the moon was made when a planet the size of Mars--called the "impactor"--smashed into proto-Earth, a junior-sized version (60-70 percent of the size) of our planet today, experts say. It was thought that during this collision, a piece of the impactor spun off and formed the moon.

The data from this study showed the tungsten composition of moon rock was identical to that on Earth--unlikely to be a mere coincidence, experts say. "We shouldn't expect the giant impactor that hit the earth--that formed the moon--to be essentially the same as Earth," says geochemist Alan Brandon of NASA's Johnson Space Center in Houston, Texas, who published a corresponding Nature paper describing the results. This suggests that the moon wasn't made of the impactor, as previous models suggested, but of proto-Earth. "Generally this has been the model that everybody has used," Brandon says, adding "so it is kind of Earth-shaking to find out now that it's different."

--Flora Lichtman