THERE is now considerable evidence to support the view that supernovae can be caused by the explosive ignition of degenerate material in evolved stars1. The conditions leading to such ignition have recently been investigated by Arnett (ref. 2 and private communication). Explosive carbon-burning produces elements ranging from Ne to Si, and silicon-burning produces elements from P to Ni. The relative abundances of elements produced in both processes are similar to the observed solar values, which supports the view that supernova explosions are a major source of enrichment of the interstellar medium in heavy elements.