Rock of ages

If you wanted to bring back a sample of some of the oldest material in the solar system, you couldn't do much better than the asteroid 234 Barbara. It lies in the main asteroid belt between Mars and Jupiter and astronomers say it's one of a trio they've found that represent the most ancient asteroids yet detected – some 4.55 billion years old.The key to dating them lies in a unique blend of calcium and aluminum – among the first compounds thought to have condensed out of the nebula of dust and gas from which the solar system formed. A team led by University of Maryland astronomer Jessica Sunshine dated the asteroids through an analysis of the minerals' blend in meteorite samples, studies of the three asteroids, and some modeling.

They concluded that these three have remained largely free of the mixing and jumbling that have substantially altered thousands of other asteroids since the solar system formed. They contain two to three times more of these aluminum-calcium "inclusions" – and so are far older – than any meteorite that has fallen to Earth.

Knowing where these time capsules are, the team says, scientists could develop approaches to return samples. These would yield key insights into processes that took place during the first few million years the solar system was forming. The results appear in the current issue of the journal Science.