It's not unheard of for a newly found birth certificate to show that someone isn't really the age they've always said -- or even thought. Usually, it shows that they're a little older than they claimed. But in the case of the Moon, it may show that it's a little younger than scientists have thought.
The Moon probably was born when a body as big as Mars slammed into Earth when the solar system was still quite young. The impact vaporized much of Earth and the other body, blasting a disk of debris into orbit. Within a millennium, this material cooled and coalesced to form the Moon.
Scientists try to read the Moon's "birth certificate" in its rocks -- in the ratios of different radioactive elements. Most readings have said the Moon was born about 30 million to 50 million years after Earth.
But last year, a team of Swiss geochemists read the record differently. Its reading says the Moon was born a little later than that -- 60 million to 100 million years after Earth.
All of these analyses of the Moon's age are based on the rock and soil returned to Earth by the Apollo astronauts. But the samples are limited, and some have already been used up; more about that tomorrow. We may need samples from future missions to resolve the truth about the Moon's age.
Look for the Moon scudding low across the south tonight. It's followed by the planet Jupiter, which looks like a brilliant star. It's to the left of the Moon in early evening.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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