On non-thermal nucleosynthesis of Short-Lived Radionuclei in the early solar system

The first results from the STARDUST mission revealed that refractory phases formed at a close distance from the nascent Sun have been transported to the comet forming region. Such refractory phases from meteorites (that originate from the asteroid belt), hold the ashes of Short-Lived Radionuclei (SLR) that were alive in the early solar system (ESS). We show that global energetic constraints obtained from Xray observations of young stellar objects strongly limit the amount of SLR that can be produced by nonthermal nucleosynthesis (irradiation) in the ESS. We show that Be-10 and Ca-41 can indeed be produced at levels compatible with a homogeneous distribution over the entire protoplanetary disk up to the comet forming region, but not Be-7, Al-26, Cl-36, and Mn-53. The maximum amount of irradiation-induced Al-26 can barely account for a homogeneous rocky reservoir of 2-3 Earth mass. We show here that, even considering a heterogeneous distribution of Al-26 in the ESS, an irradiation origin of this preeminent isotopic chronometer is unlikely. (C) 2008 Elsevier B.V. All rights reserved.