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WHEN the sun dies, it’s not just Earth that will be doomed – the destruction will reach as far as the comets in the outer solar system. That’s according to a new explanation of the behaviour of planetary nebulae – bubbles of gas sloughed off by dying stars (pictured).

There are two methods for calculating the abundance of elements in planetary nebulae: looking at light emitted when electrons and ionised atoms recombine, or looking at the energy emitted by atoms excited by collisions. Yet they yield very different results, a discrepancy that has baffled astronomers for decades.

Now William Henney of the National Autonomous University of Mexico in Mexico City and Grazyna Stasinska of the Paris Observatory in France suggest that material from vaporised comets could be skewing the recombination method’s result. This is because pockets of gas rich in heavy elements would be created if a comet in the outer regions of a solar system got vaporised by a dying star in its red giant phase or by the expanding planetary nebula that follows it ().