What Hit Sudbury?

The Sudbury basin is a 30-by-60 km hole in the Canadian Shield, visible from space, that is, in fact, the deformed remains of a crater created by a cosmic impact, 1.85 billion years ago.  New work by Joe Petrus, a PhD student in Earth Sciences at Laurentian University, and his colleagues, has now pointed at the identity of the crater-creator. Sensitive chemical analysis of the melted debris from the impact gives a signature of the object, which had to be either an asteroid or a comet. But the energy of the impact and the dilution of the geochemical trace suggests that it was a comet - a combination of ice and rock that slammed into what would become Sudbury.

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