They reveal the origin of wine, the age of bones and fossils, and they serve as diagnostic tools in medicine. Isotopes and isotopologues—molecules that differ only in the composition of their isotopes—also play an increasingly important role in astronomy. For example, the ratio of carbon-12 (12C) to carbon-13 (13C) isotopes in the atmosphere of an exoplanet allows scientists to infer the distance at which the exoplanet orbits its central star.
