Wrede, an assistant professor of physics at Michigan State University, told Live Science in an email that researchers look at the grains' isotopes - variations of an element that have different numbers of neutrons. About a dozen grains held a great deal of the isotope silicon-30, which has been linked to a certain type of stellar explosion called a classical nova.
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Classical novas - stellar eruptions that happen in a binary, or paired, star system - are different from supernovas, Wrede said, in that they are a type of explosion that can happen over and over again. The smaller star in a pair, a white dwarf, steals fuel from its larger neighbor, heating up its own surface and eventually blasting dust and gas into space.
"After a classical nova, the white dwarf can continue to siphon fuel from the companion and ignite again," Wrede said. "In a supernova, the entire star explodes, so it can only happen once."
Going Nuclear When Earth's solar system was forming, collisions heated and mixed the building blocks of dust and gas, cooking them uniformly so that they shared many of the same isotopes. Grains with unusual isotopes - like silicon-30, which is rare on Earth - stand out, Wrede explained. "This tells us that they must have been produced prior to the formation of the solar system," dating back around 5 billion years, Wrede said.