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September 22, 2008 | by  | in Opinion | [ssba]

Iron Meteorites

Kimberly Andrews is a Master’s student in the School of Geography, Environment and Earth sciences, and her thesis is studying the possibility of a supernova playing a part in the formation of the solar system.

She does this by analysing the levels of 60Ni in samples of iron meteorites (bought online), which represent the oldest known objects from the early solar system. 60Ni is a naturally occuring isotope of nickel, but is also the stable product of radioactive decay from 60Fe, an isotope that can only form in a supernova. If the amount of 60Ni present in these samples is consistently above or below the level on Earth, then this is evidence that there was a supernova present at or immediately before the formation of the Solar System.

The process of measuring the level of 60Ni is painstaking. Each meteorite must first be prepared, grinding off a piece of meteorite, and then polishing it to remove any contamination from the surface of Earth. The sample is then dissolved in acid, and through a complex process of filtering reduces the sample to nickel only. This final sample of nickel is then analysed using a mass spectrometer to determine the proportion of 60Ni in the sample compared to other possible isotopes.

So far Andrews has analysed samples from 11 different meteorites, and has found levels of 60Ni lower than those found on Earth. This, paradoxically, suggests that a supernova did play a part in the formation of the solar system. The iron meteorites she has been analysing come from the core of early planetesimals, so will have been exposed to much less solar 60Fe than crust and mantle. Earth provides a baseline, as it was formed much later, once these planetesimals had combined producing a consistent level of 60Ni throughout.

Each nickel sample to be analysed with the mass spectrometer must be accompanied by two Earth samples; one before and one after. This gives the ‘default’ level of nickel-60 to be found in a sample of nickel, and using two measurements gives an idea of the margin of error.

For each meteorite, 10 samples of nickel must be taken, and each of these must be accompanied by two control samples from Earth. Each measurement takes 30 minutes. In the month of April, before a new machine was acquired, Andrews was running the machine continuously, 24 hours a day. She was required to attend to the machine every 5 hours, so was getting up at 3am, 8am, 1 pm et cetera throughout.

Andrews is also looking at other stellar-produced isotopes of nickel to see how homogenous the distribution is. However, because Iron-60 has such a short half-life, it is now extinct in the solar system, so anomalous levels of 60Ni are clear evidence that a supernova played a part in solar system formation. She has found that the other isotopes are all fairly homogenous across samples, so the reduced levels of 60Ni cannot be explained purely by sample bias.

There are four other labs around the world doing similar work. Andrews’ results have not correlated with the results of other labs, and has consequently been highly controversial. Andrews has tested samples from a meteorite sent from another lab, and her results fit her own trend, rather than those of the lab from which the meteorite came. However, a recently published study has reinforced her results, suggesting any methodological errors have arisen with the lab she received the meteorite from.

Kimberly Andrews holds a BSci in Biology and Geology. She has recently presented her work at seminars in Hawaii and British Columbia.


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