Could a Supernova Wipe Out Life on Earth ?

   

A supernova is a stellar explosion. Incredibly strong, a typical supernova can outshine an entire galaxy at its peak, ejecting a Sun’s worth of stellar mass at a significant fraction of the speed of light within seconds. And here’s the harsh reality: A supernova, if it were close enough, could certainly spell the end of civilization and, perhaps, wipe out all life on Earth. As heavy radioactive elements in the ejected matter decayed, they would produce gamma rays.

    

     These gamma rays would be powerful enough to convert our ozone layer into nitrogen oxides and pure nitrogen, neither of which would protect us from the radiation of space.

    

     The bombardment of solar and cosmic rays would destroy key parts of the ecosystem, especially plankton and coral reefs. With the collapse of these systems, the oceanic biome would likely collapse, leading to a mass extinction that would vibrate across the food chain. Given long enough exposure, the bombardment of cosmic and solar rays would threaten and, eventually, wipe out surface life— including humankind—everywhere. If any life survived, it would likely be microbes hiding deep inside Earth’s crust.

    

     As scary as this scenario is, it is also extremely unlikely. In cosmic terms, that supernova would have to be awfully close to cause any real damage. Powerful, Type Ia supernovas dim significantly beyond 75 light-years, and less powerful Type II supernovas are unlikely to cause significant damage at a distance greater than 25 light-years. Thankfully, there are no stars close enough and massive enough to go supernova. The nearest candidate is IK Pegasi, safely 150 light-years away (and creeping even further away from us). Luckily for us, of the 200 to 400 million stars in the Milky Way, an average of three go supernova every century. This isn’t something we have to worry about any time soon.