Mass-independent fractionation of titanium isotopes and its cosmochemical implications

Isotopes of heavy elements are produced in various amounts by nuclear processes in stars1,2. Consequently, the presence of isotopic anomalies in the Solar System is considered to reflect the presence of presolar grains condensed in previous generations of stars3 and not a (proto-) Solar System process. However, for oxygen, the major rock-forming element, it has been shown that physico-chemical reactions applicable to the presolar cloud or the protoplanetary disk were a possible source of isotopic variations due to mass-independent isotopic fractionation (MIF)4,5. Here we show that MIF effects are not restricted to oxygen, but can also be produced for titanium. Titanium-rich grains experimentally condensed from a TiCl4(g)/C5H12(g) plasma exhibit MIF effects from −25% to +120% for all Ti isotopic ratios. These large Ti isotopic variations follow the model developed for oxygen MIF6 and mimic the Ti isotopic anomalies observed in some presolar grains. This effect is ascribed to the reactions between chemically indistinguishable isotopes6 and could contribute to the complexity of isotopic anomalies observed in Solar System materials1,7–14. The abundances of isotopes in presolar grains are presumed to reflect their nucleosynthetic generation in stars. However, here Robert et al. report experimentally detected evidence of mass-independent fractionation of titanium, implying that titanium isotopic abundances in presolar grains may not be as representative as once thought.