Computer Science
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005psrd.repte..94t&link_type=abstract
Planetary Science Research Discoveries
Computer Science
Meteorite, Chondrule, Cosmochemistry, Cai, Oxygen Isotope
Scientific paper
Chondrules and calcium-aluminum-rich inclusions (CAIs) in stony meteorites called chondrites are silicate objects only fractions of a millimeter to several millimeters in diameter. Both formed during rapid heating events at the dawn of the solar system, before there were planets. Conventional wisdom, based on numerous observations and isotopic analyses, indicates that CAIs formed before chondrules. CAIs contained more radioactive aluminum-26 (which has a half-life of only 730,000 years) when they formed than did chondrules, indicating that they formed 1-3 million years earlier. Relict pieces of CAIs have even been found inside chondrules, and so must have formed earlier. However, Shoichi Itoh and Hisayoshi Yurimoto of the Tokyo Institute of Technology found a chondrule inside a CAI, the reverse of the normal situation, which indicated that some chondrules must have formed before CAIs, a blow to the conventional wisdom.
Alexander (Sasha) Krot (University of Hawaii), Professor Yurimoto from Tokyo, Ian Hutcheon (Lawrence Livermore National Laboratory), and Glenn MacPherson (Smithsonian Institution) report two additional cases of chondrules inside CAIs. They show that in both cases the CAIs contained less 26Al when they crystallized than did most CAIs. The CAIs are also depleted in oxygen-16, a characteristic associated with chondrules. Durable minerals located in the central parts of the two CAIs have oxygen-16-rich compositions. Krot and his co-workers conclude that the two chondrule-bearing CAIs had chondrule material added to them during a reheating event about 2 million years after they had originally formed. The conventional wisdom that CAIs are older than chondrules remains intact, at least for now, but this work shows that CAIs, like most solar system materials, can be reworked after they form.
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