Working Out The Source Of Shooting Star Samples

Meteorites, being literally not of this world, show intrinsic differences to rocks found on Earth. Very specifically the ratio of isotopes present in meteors tells us what the isotope ratios were in the places the meteors were likely to form. The difficulty comes in assigning which environment and specifically which star type was likely to have a created the particular proportions of isotopes.  A puzzle is created due to the fact that although stars with masses between four and eight times our own sun should have produced a good number of meteorites none have ever been found with confirmed isotope ratios matching these stars. These are the kinds of inconsistencies what plague a physicists mind because it shows that somewhere in the theory a mistake has been made.

There has been some progress towards answering this question with a recent paper discussing the development of the isotope oxygen-17. Through proton addition from smaller elements oxygen-17 is believed to be created when temperatures reach about 70,000,000 K. This temperature and the experimental ratio of oxygen-16/17 found in the meteorite remnants matches the conditions during the end part of a star between four and eight solar masses lifetime. Similar results were also found for the isotopes of magnesium and aluminium with which the ratios are most accurately explained by scenarios where protons are in such a high energy state they can be added to nuclei, a process known as proton burning. Since this would be expected in the described solar mass range this provides the missing evidence for meteorites produced in this way. This theory also explains why not many fragments of meteorites with these isotope ratios are found; the extreme temperatures present during their formation resulted in much of the evidence being destroyed and even the amount that did was likely trapped by the protosolar nebula and eventually became our star. Now by looking at the isotope ratios it is possible to deduce some qualities of the original stars and since stars of this mass, called asymptotic giant branch stars, are a rare observation this method could become very useful.

Paper links: Origin of meteoritic stardust unveiled by a revised proton-capture rate of 17O


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