Iron-60
Iron-60 is a short-lived radioactive isotope made in massive stars; its amount in the early Solar System is debated.
Iron-60 is a radioactive isotope of iron with a half-life of about 2.6 million years. It decays to cobalt-60 and then to nickel-60. Unlike aluminium-26, iron-60 is made almost entirely in massive stars and supernovae, not by cosmic rays, so its abundance in the early Solar System is a test of whether a stellar explosion contributed to the young Sun's cloud.
Measurements in meteorites have given conflicting answers. Some early studies suggested high levels of iron-60, implying a nearby supernova. More recent, precise measurements on bulk meteorites and chondrules found much lower values, consistent with the general background of the galaxy.
Iron-60 has also been found on Earth, in deep-sea crusts and Antarctic snow, deposited by supernovae within the last few million years. In meteoritics, it remains a puzzle that touches the question of the Sun's birthplace: in a quiet region, or close to massive stars about to explode.
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