What is the isotopic dichotomy in meteorites?

In the 2010s, scientists discovered that meteorites split cleanly into two families when they measured certain isotopes. This is the isotopic dichotomy.

The isotopes involved, such as chromium-54, titanium-50 and molybdenum isotopes, vary slightly because the Solar System inherited material from different stars that was not perfectly mixed. When meteorites are plotted using these isotopes, they fall into two clusters with a clear gap.

- The non-carbonaceous or NC family includes ordinary chondrites, enstatite chondrites, most achondrites, including HED meteorites from Vesta and Martian meteorites, and many iron meteorite groups. Earth and the Moon also belong to this family. - The carbonaceous or CC family includes all carbonaceous chondrites and some iron meteorite groups.

The two families are thought to represent the inner and outer Solar System. The gap suggests that something kept the two regions apart for several million years. The most popular explanation is that Jupiter's core formed very early, within about a million years, creating a gap in the disc that blocked material from drifting inwards. Another idea involves a pressure bump in the disc.

The dichotomy is a powerful tool. It allows scientists to tell whether a meteorite or planet formed from inner or outer Solar System material. Earth seems to be mostly NC material with a small addition of CC material, which may have delivered some water and volatiles. The dichotomy also shows that outer Solar System material, like CC meteorites, later reached the asteroid belt.

More about the science of meteorites

• Did Jupiter affect which meteorites reach Earth?
• What can meteorites tell us about the Moon's origin?
• Why are there no known meteorites from Mercury or Venus?
• What is the most common type of meteorite to fall?
• Do meteorites contain sugars or DNA building blocks?
• How do scientists stop meteorites being contaminated?

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