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Supernova shrapnel
found in meteorite

Posted: 10 September 2010

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Traces of an ancient supernova event have been identified in a meteorite, explaining the curious chemical fingerprints found in the rock.

Chromium 54 is the cosmic chemical that has fallen under the scrutiny of University of Chicago cosmochemist Nicolas Dauphas and colleagues, which is found to vary from one planet and meteorite to another. This was unexpected, since all elements are thought to have been evenly spread throughout the cloud of gas and dust that collapsed to form our Solar System.

“It was a very well-mixed soup,” says Clemson University professor Bradley Meyer, who was not involved in the new study. “But it looks like some of the ingredients got in there and didn’t get completely homogenized, and that’s a pretty interesting result.”

The Crab nebula is one of the most well-known supernova remnants. Image: NASA, ESA, J. Hester and A. Loll (Arizona State University).

Scientists suspect that a supernova occurred around 4.5 billion years ago, possibly triggering the birth of our Sun – the evidence coming from traces of aluminum 26 and iron 60, two short-lived isotopes found in meteorites but not on Earth. “It seems likely that at least one massive star contributed material to the Solar System or what was going to become the Solar System shortly before its birth,” says Meyer.

Aluminum 26 and iron 60 could have been generated in a Type II supernova, caused by the core-collapse of a massive star. While supernova shrapnel from Type II supernova have been extracted from meteorites before, they have not been identified from Type Ia supernova, which result from the explosion of a white dwarf binary star. Dauphas and his team hope to identify which supernova type contributed the chromium 54 found in the meteorite that they were studying, the Orgueil meteorite. Just one grain, measuring less than 100 nanometres in diameter (1,000 times smaller than the diameter of a human hair) was found to contain an excess of chromium 54.

The scientists speculate that the ancient supernova event sprayed finely grained particles of different elements into the birthing pool of the Solar System, where dynamical processes sorted the grains by size, such that they become disproportionally incorporated into the meteorites and planets newly forming around the Sun.

“It’s remarkable that you can look at an isotope like chromium 54 and potentially find out a whole lot about what happened in the very first period of the Solar System’s formation,” says Meyer.

“The test will be to measure calcium 48,” adds Dauphas. “You can make it in very large quantities in Type Ia supernovae, but it’s very difficult to produce in Type II.” So if the team find grains that are highly enriched in calcium 48, they no doubt came from a Type Ia supernova.

The results of the study are reported in the 10 September issue of the Astrophysical Journal.