Electron microscope image of pre-solar particles extracted from primitive meteorites. Image credit: NASA, Liu Nan and Andrew Davis.

Presolar particles are small pieces of solid interstellar material that condense in the gas flowing and cooling from different types of stars before the formation of the sun. After traveling through interstellar space, some presolar particles are embedded in the material that becomes meteorites in our solar system. Most of the pre-solar particles found in meteorites are carbonaceous materials such as diamond, silicon carbide (SiC) and graphite. Studying the unique chemical, isotopic, and physical properties of pre-solar particles can provide detailed information about the nucleosynthesis and stellar evolution of stars outside the sun.

A research team led by Nan Liu of Washington University in St. Louis examined 85 sub-micron to micron-sized pre-solar SiC particles found in Murchison carbonaceous chondrites to determine their isotopic composition and better understand Their stellar origin. The multi-element isotope data of carbon, nitrogen, silicon, titanium, magnesium, and aluminum in these particles were measured with a NanoSIMS mass spectrometer. This work shows that most pre-solar particles have a layer of pollutants, whether they are land or from surrounding host meteorites. This pollution must be removed or avoided in order to obtain the inherent isotope data from the pre-solar particles. In some cases, the high spatial resolution of NanoSIMS images can avoid contamination. The results indicate that previous data on pre-solar particles may include pollution and may not reflect the true isotopic composition of the particles. The new, pollution-free isotope data of pre-solar particles obtained in this work shows that hydrogen fusion (that is, the nuclear fusion of four protons to form a helium nucleus) occurs in the parent carbon star of the pre-solar particle, and the temperature is higher than previously thought The new isotope data will help astrophysicists build more accurate models of star formation and evolution. read more