Planetary Science

No Stellar Explosion Needed

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Science  18 Jan 2013:
Vol. 339, Issue 6117, pp. 251
DOI: 10.1126/science.339.6117.251-b

The presence of the decay products of short-lived radioactive isotopes in meteorites provides clues to the astrophysical context of the formation of our solar system. Iron-60, for example, can only be produced in stellar explosions; given its half-life of 2.62 million years, a high abundance of this radioisotope in early solar system materials would imply that a star exploded in the vicinity of the newborn Sun. The abundance of 60Fe, an extinct radioisotope, can be constrained by measuring isotopic variations in its decay product 60Ni: a stable isotope of nickel. Previous estimates disagree, depending on the materials analyzed, which has been interpreted as reflecting heterogeneous distribution of 60Fe among planetary bodies. Based on high-precision and high-accuracy 60Ni and 58Fe isotope measurements of a variety of meteorites, Tang and Dauphas now show that, contrary to previous results, the initial abundance of 60Fe in the early solar system was uniformly low, precluding the need for a nearby stellar explosion around the time the solar system formed. Instead, 60Fe may have been inherited from the interstellar medium as the result of the long-term chemical evolution of our galaxy.

Earth Planet. Sci. Lett. 359-360, 248 (2012).

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