Isotopic dichotomy
The isotopic dichotomy is the split of meteorites into two isotopic families, non-carbonaceous and carbonaceous, from the inner and outer Solar System.
In 2011, a study of chromium, titanium and oxygen isotopes showed that meteorites fall into two distinct families with almost no overlap. This is the isotopic dichotomy. One family, called non-carbonaceous or NC, includes ordinary and enstatite chondrites, most achondrites such as eucrites, and several iron groups. The other, called carbonaceous or CC, includes carbonaceous chondrites and some iron groups such as IID, IIIF and IVB.
The differences arise from small nucleosynthetic variations, inherited unevenly from the cloud that formed the Solar System. They are thought to reflect two reservoirs, the inner and outer Solar System, that stayed apart for several million years.
The leading explanation is that the young Jupiter grew rapidly, within about a million years, and its gravity created a barrier that stopped material from mixing across its orbit. Iron meteorites from both families formed early, showing both reservoirs were busy making planetesimals. The dichotomy has become a powerful tool for tracing where planets got their ingredients.
Related terms
Level: Expert Advanced