Stable isotope
A stable isotope is a form of an element whose nucleus does not decay over time.
Every element has atoms with the same number of protons but different numbers of neutrons. These versions are isotopes. A stable isotope has a nucleus that does not break down, so the amount of it stays the same forever unless something else changes it.
Oxygen, for example, has three stable isotopes: oxygen-16, oxygen-17 and oxygen-18. Carbon has two, carbon-12 and carbon-13. The ratios between stable isotopes vary slightly from place to place, because physical and chemical processes such as evaporation and condensation sort them by mass, and because different reservoirs in the early Solar System inherited different mixtures.
In meteoritics, stable isotopes are fingerprints. Oxygen isotopes separate meteorites from different parent bodies, nitrogen and hydrogen isotopes trace the origins of organic matter and water, and isotopes of chromium, titanium and molybdenum reveal whether a meteorite formed in the inner or outer Solar System.
Related terms
Level: Explorer Ages 10 and up