Whence the Solar System?

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Science  25 Jun 2010:
Vol. 328, Issue 5986, pp. 1613
DOI: 10.1126/science.328.5986.1613-b

Primitive materials within meteorites hold evidence for processes that occurred during the earliest stages of the solar system. In particular, the inclusion of the daughter products of now-extinct, short-lived radioisotopes tells us that the parent isotopes were active at the time they were incorporated into the solar system's earliest solids. One such isotope is 60Fe, whose origin is attributed to either a core-collapse supernova (the thermonuclear explosion of a massive star) or an intermediate-mass asymptotic giant branch (AGB) star. Sun-like stars end their lives as AGB stars; in the late stages of their evolution, these stars expel their outer envelopes and shine as planetary nebulae as their hot surfaces are exposed and ionize material around them. The ejecta of AGB stars or supernovae drive shock fronts into the interstellar medium, a process posited to have triggered the collapse of the cloud from which the Sun formed and then injected freshly synthesized radioisotopes into it. Using numerical simulations to test both scenarios (supernova versus AGB), Boss and Keiser show that only supernovae have thin enough shock waves to inject the material necessary to match the abundances of short-lived radioisotopes measured in primitive meteorites.

Astrophys. J. 717, L1 (2010).

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