COULD A SUPERNOVA WORDS ANDREW MAY ENGULF EARTH?

We put some intriguing, baffling and bizarre space questions under the spotlight

A supernova is what happens when a large enough star explodes. Such explosions are among the most dramatic of all astronomical events, and the resulting remnant can be a spectacular sight thousands of years later. Fortunately, supernovae are relatively rare, and we’re very unlikely to get caught up in one. The most disastrous thing from our perspective would be if our own Sun went supernova, but this will never happen. Only two types of star are capable of exploding in such a dramatic fashion: super-dense white dwarfs orbiting larger companion stars, which can produce Type I supernovae, or stars with at least eight times as much mass as the Sun, which end their lives as Type II supernovae. Our Sun isn’t in either of these categories.

Even so, this doesn’t mean that Earth can never be harmed by a supernova – in theory, at least. As well as producing the visible remnant, a supernova creates a burst of high-energy radiation that travels outwards at the speed of light. This radiation, particularly the highest energy gamma rays, could damage Earth’s biosphere if it came from the explosion of a nearby star. A sudden burst of gamma rays hitting the upper atmosphere could convert nitrogen and oxygen into smog-like nitrogen oxides, as well as damaging the ozone layer that protects Earth’s surface from the deadliest frquencies of ultraviolet radiation.

These effects would be particularly catastrophic for marine life. Scientists have speculated that just such a gamma-ray burst around 450 million years ago caused the Late Ordovician mass extinction, which saw the death of around 60 per cent of all oceanic life on Earth.