Which came last—The supernova or the red giant?

Science Focus

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A red giant star really is quite gigantic compared to our Sun.

NASA

Radioactive decay is a powerful tool. The predictable decay of radioactive isotopes can be used for far more than just dating old rocks. Scientists have used radioactive isotopes to determine the age of the Earth and the age of the Solar System itself. Now, a team of scientists has used radioactive dating to study the pre-history of the Solar System more accurately than before, in the process reconciling data that had seemed to be contradictory.

The contradiction came in the form of data from two different isotopes. The radioactive elements iodine-129 and hafnium-182 are found throughout meteoroids in the Solar System. The abundance of those elements, in relation to the abundance of their non-radioactive counterparts, should give estimates of the time when those elements were produced. The problem is that the date calculated from the iodine (~72 million years prior to the Sun’s formation) does not match the date from the hafnium (~15 million years). Since the two elements should have been produced in the same event (typically a supernova), this was quite a problem.

Both these isotopes are produced via a neutron-capture process. Under certain conditions, an atomic nucleus can pick up a loose neutron. While it remains the same element, it ends up being a different isotope with a different atomic weight. There are two known types of neutron-capture processes: the s-process and the r-process.

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