A new study, published by University of Chicago researchers challenges, the notion that the force of an exploding star forced the formation of the solar system.
In this study, published online in Earth and Planetary Science Letters in November 2012, authors Haolan Tang and Nicolas Dauphas found the radioactive isotope iron 60 – the telltale sign of an exploding star – low in abundance and well mixed in solar system material.
As cosmochemists, they look for remnants of stellar explosions in meteorites to help determine the conditions under which the solar system formed. Some remnants are radioactive isotopes, that is, unstable, energetic atoms that decay over time. Scientists in the past decade have found high amounts of the radioactive isotope iron 60 in early solar system materials. “If you have iron 60 in high abundance in the solar system, that’s a ‘smoking gun’ – evidence for the presence of a supernova,” Dauphas, professor in geophysical sciences, told me during a meeting in his office in October 2012.
Iron 60 can only originate from a supernova, so scientists have tried to explain this apparent abundance by suggesting that a supernova occurred nearby, spreading the isotope throughout the explosion. However, Tang and Dauphas’ results were different from previous work. They discovered that levels of iron 60 were uniform and low in early solar system material. They arrived at these conclusions by testing meteorite samples. To measure iron 60’s abundance, they looked at the same materials that previous researchers had worked on, but used a different, more precise approach that yielded evidence of very low iron 60.
Previous methods kept the meteorite samples intact and did not completely remove impurities, which may have led to greater errors in measurement. However, Tang and Dauphas’ approach required that they ‘digest’ their meteorite samples into solution before measurement, which allowed them to thoroughly remove the impurities. This process ultimately produced results with much smaller errors. “Haolan has dedicated five years of very hard work to reach these conclusions, so we did not make those claims lightly. We’ve been extremely careful to reach a point where we’re ready to go public on those measurements,” Dauphas remarked.
To address whether iron 60 was widely distributed, Tang and Dauphas looked at another isotope of iron: iron 58. Supernovae produce both isotopes by the same processes, so they were able to trace the distribution of iron 60 by measuring the distribution of iron 58. “The two isotopes act like inseparable twins: once we knew where iron 58 was, we knew iron 60 couldn’t be very far away,” Dauphas explained.