Solar system older than estimated

Meteorite age suggests planets began to form earlier than thought

The solar system may be almost 2 million years older than previously thought, a new study shows.

WHAT’S IN YOUR POCKET? A pocket of calcium- and aluminum-rich material (light area) in a meteorite may be the remains of some of the first solids that formed in the solar system. The rock puts the age of the solar system up to 1.9 million years older than previously estimated. A. Bouvier and M. Wadhwa/Nature 2010

Data from a newly studied meteorite recovered from the Saharan Desert show that the solar system formed 4,568.2 million years ago, 0.3 million to 1.9 million years earlier than other estimates. The results were published online August 22 in Nature Geoscience.

“All the interesting things we want to understand about the chemistry of our solar system happened within the first five to 10 million years,” says study coauthor Meenakshi Wadhwa, a cosmochemist from Arizona State University in Tempe. “When you push it back by 2 million years, that’s a substantial proportion of that 5 to 10 million years.”

The meteorite contains millimeter- and centimeter-sized bits of calcium- and aluminum-rich substances, some of the oldest material ever found in primordial rocks. These pockets in the rock, called inclusions, are believed to be among the first solids that condensed from gas at the beginning of the solar system’s formation. Along with other materials in the presolar cloud, the inclusions snowballed into larger objects, eventually forming asteroids and planets.

Study coauthor Audrey Bouvier of Arizona State measured the ratios of variants of lead atoms produced by the radioactive decay of uranium present when the inclusions formed.  Since uranium decays at a known rate, current amounts of lead forms, or isotopes, allow scientists to calculate how long ago the space dust formed.

Two meteorites previously analyzed for their lead-isotope ratio suggested the first solar system solids formed 4,567.1 million to 4,567.6 million years ago. But these ages were inconsistent with other radioactive “clocks” in the same rocks, such as one based on the decay of an aluminum isotope to magnesium.

The uranium-lead decay age is consistent with other clocks in the new meteorite. The rock probably went through less heating and bombardment when it was part of an asteroid than the previously studied meteorites did, the authors say, so it experienced less chemical change.

The softball-sized meteorite was found in Morocco in 2004 and weighs a little over three pounds.

“It’s like crime-scene investigation four and a half billion years after the scene is vacated,” says astrophysicist Alan Boss of the Carnegie Institution for Science in Washington, D.C. “We’re coming toward more of a cohesive picture of how things happened.”

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