Irradiation in the early solar system and the origin of short-lived radionuclides

Abstract

The origin of short-lived ( T ∼ 1 Myr) radionuclides (SRs) in the early solar system is a matter of debate. Some short-lived radionuclides had abundances in the solar protoplanetary disk in excess compared to the expected galactic background ( Be 7 , Be 10 , Al 26 , Cl 36 , Ca 41 and possibly Mn 53 and Fe 60 ). These SRs thus either originated from a supernova contamination, or were produced by in situ irradiation of solar system dust or gas, or by Galactic Cosmic Ray (GCR) trapping in the molecular cloud core progenitor of our solar system (for Be 10 only). GCR trapping in the molecular cloud core seems to fail to reproduce the initial abundance of Be 10 , because trapping timescales exceed by one order of magnitude the observed core lifetimes. On the other hand, irradiation models can synthesize large quantities of Be 10 and other SRs ( Be 7 , Cl 36 , Al 26 , Ca 41 and Mn 53 ). In addition, X-ray observations of young, solar-like stars provide direct evidence for protoplanetary disk irradiation in a different energy window. The initial abundance of Fe 60 is poorly known, and its presence in the early solar system might be accounted for galactic abundance rather than by a nearby supernova.