Thursday, April 21, 2005
Chock Full of Chondrules
Scientists at the Lawrence Livermore National laboratory studying an ancient meteorite say they have determined the age of the solar system. By their counting, our cosmic neighborhood started condensing from a cloud of interstellar dust and gas between 4.567 billion and 4.565 billion years ago.
The scientists made the discovery by studying chondrules, milimeter-sized spheres thought to be among the first solids to have formed in the solar nebula, and "calcium aluminum inclusions" called CAIs.
Chondrules and CAIs have never been found in any terrestrial rocks, but they are often embedded in space rocks like the massive Allende meteorite, which crashed in Mexico in 1969 and scattered tons of debris over 100 square miles.
Both chondrules and CAIs contain strange isotopic signatures that pointed to their birth before the solar system formed. The assumption was that these tiny objects were probably the product of a nearby supernova.
The Livermore scientists working hand in had with researchers in Hawaii, Tokyo, the Smithsonian and MIT dated the oxygen 16 isotope present in Allende's chondrules and CAIs to crack the riddle. They discovered that the CAIs and chondrules were born about two million year apart, but tens of millions of years before any planets in the solar systems. Earth and the rest of the solar rocks are thought to have formed about 4.5 billion years ago.
"Over this span of about two million years, the oxygen in the solar nebula changed substantially in its isotopic makeup," said Livermore's Ian Hutcheon. "In the past the age difference between CAIs and chondrules was not well-defined. Refining the lifetime of the solar nebula is quite significant in terms of understanding how our solar system formed."
The scientists made the discovery by studying chondrules, milimeter-sized spheres thought to be among the first solids to have formed in the solar nebula, and "calcium aluminum inclusions" called CAIs.
Chondrules and CAIs have never been found in any terrestrial rocks, but they are often embedded in space rocks like the massive Allende meteorite, which crashed in Mexico in 1969 and scattered tons of debris over 100 square miles.
Both chondrules and CAIs contain strange isotopic signatures that pointed to their birth before the solar system formed. The assumption was that these tiny objects were probably the product of a nearby supernova.
The Livermore scientists working hand in had with researchers in Hawaii, Tokyo, the Smithsonian and MIT dated the oxygen 16 isotope present in Allende's chondrules and CAIs to crack the riddle. They discovered that the CAIs and chondrules were born about two million year apart, but tens of millions of years before any planets in the solar systems. Earth and the rest of the solar rocks are thought to have formed about 4.5 billion years ago.
"Over this span of about two million years, the oxygen in the solar nebula changed substantially in its isotopic makeup," said Livermore's Ian Hutcheon. "In the past the age difference between CAIs and chondrules was not well-defined. Refining the lifetime of the solar nebula is quite significant in terms of understanding how our solar system formed."
