A Late Episode of Irradiation in the Early Solar System: Evidence from Extinct 36 Cl and 26 Al in Meteorites

Abstract

Late-formed halogen-rich phases in a refractory inclusion and a chondrule from the Allende meteorite exhibit large 36S excesses that linearly correlate with the chlorine concentration, providing strong evidence in support of the existence of the short-lived nuclide 36Cl (mean life of 0.43 Myr) in the early solar system. The inferred 36Cl/35Cl ratios at the time when these phases formed are very high (∼4 × 10-6) and essentially the same for the inclusion and the chondrule and confirm the earlier report of 36S excess in another meteorite. In addition, the 36Cl is decoupled from 26Al. The observed and any possible higher levels of 36Cl cannot be the result of a supernova or AGB stellar source but require a late episode of energetic particle bombardment by the early Sun, in support of the arguments based on the previous discovery of 10Be. It is now clear that a blend of several sources is required to explain the short-lived nuclei when the solar system formed. © 2006. The American Astronomical Society. All rights reserved.