Magazine article Science News

Aluminum Emerges as Early Timekeeper

Magazine article Science News

Aluminum Emerges as Early Timekeeper

Article excerpt

It isn't easy trying to determine when objects formed in the early solar system. What planetary scientists need is an accurate timekeeper, and a new study supports the notion that a short-lived isotope of aluminum fills the bill.

By analyzing some of the oldest known bits of rock, the scientists say, they have found strong evidence that aluminum-26 was widespread in the early solar system. The isotope's ubiquity, together with its half-life of only 730,000 years, gives researchers a means of clocking key events during the first few million years of the solar system's existence.

Because earlier objects would capture a higher proportion of this isotope, its relative abundance in asteroids and other rocky bodies provides a clue to when they were formed. Some of these bodies provided the building blocks for planets.

Scientists have known since the 1970s that significant amounts of aluminum-26 resided in some meteorites that have fallen to Earth. However, these ancient rocks, called carbonaceous chondrites, are rare, so astronomers had no guarantee that this aluminum isotope was widely distributed and bore witness to events throughout the newborn solar system.

In the new study, Glenn J. MacPherson of the National Museum of Natural History in Washington, D.C., and his colleagues measured the amount of magnesium-26-the isotope produced when aluminum-26 decays-in a far more common class of meteorites, the ordinary chondrites. They deduced that, early in the solar system's existence, the ratio of aluminum-26 to its stable sister isotope, aluminum-27, had been the same in ordinary chondrites as in the much rarer carbonaceous chondrites. …

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