A STELLAR ORIGIN FOR THE SHORT-LIVED NUCLIDES IN THE EARLY SOLAR-SYSTEM

Primitive meteorites contain isotopes that are the decay products of s hort-lived nuclides in the early Solar System(1,2). The relative abund ances of these isotopes provide a means to determine timescales for th e formation and accretion of primitive Solar System objects, the abund ances of the parent nuclides being fixed when these objects solidified , The abundances can also be used to investigate the source of the nuc lides (such as Ca-41, Al-26, Fe-60, Mn-53 and Pd-107), although this i s an area of controversy. The nuclides could have originated from a si ngle stellar object(2-6), such as a nearby red-giant or a supernova. B ut observations of enhanced ion fluxes in a molecular cloud(7) have le d to other models(8-10) in which these nuclides are formed by energeti c particle irradiation of gas and dust in the protosolar molecular clo ud; alternatively, irradiation by energetic particles from the active early Sun may have occurred within the solar nebula itself(11-18). Her e we show that there is a correlation between the initial abundances o f Ca-41 and Al-26 in samples of primitive meteorite (as inferred from their respective decay products, K-41 and Mg-26), implying a common or igin for the short-lived nuclides. We can therefore rule out the mecha nisms based on energetic particle irradiation, as they cannot produce simultaneously the inferred initial abundances of both nuclides. If, a s our results suggest, a single stellar source is responsible for gene rating these nuclides, we can constrain to less than one million years the timescale for the collapse of the protosolar cloud to form the Su n.