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I've been reading about supernovae for a while, and I noticed how incredibly fast their shockwave and remnants travel shortly after the explosion. So I thought about how this would affect the earth if one happened nearby.

I know that the Earth's atmosphere already protects us from cosmic rays which I think have energy comparable to those particles from supernovae, so would a near-earth supernova be any different ? Of course I know it depends on how far the supernova is and I know that currently there are not too close stars that are about to go supernova. So for the sake of the question, let's assume it's a few light years away. Please notice that I am not asking about the possibility of something like this happening, I am just curious what it would do to earth if it does happen that close.

So what do you think the effects of such close supernova can be?

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I have never given this much thought because supernovas and stars are so far away. But I took a look at the research out there. (Note 10 parces or pc is 32.6 lightyears or ly)

A supernova explosion of the order of 10 pc away could be expected every few hundred million years, and could destroy the ozone layer for hundreds of years, letting in potentially lethal solar ultraviolet radiation. In addition to effects on land ecology, this could entail mass destruction of plankton and reef communities, with disastrous consequences for marine life as well. A supernova extinction should be distinguishable from a meteorite impact such as the one that presumably killed the dinosaurs. (near-earch supernovas)

The study continues by investigating possible past extinction events and found:

We conclude that recent observations of Geminga, PSR J0437- 4715 and SN 1987A strengthen the case for one or more supernova extinctions during the Phanerozoic era. A nearby supernova explosion would have depleted the ozone layer, exposing both marine and terrestrial organisms to potentially lethal solar ultraviolet radiation. In particular, photosynthesizing organisms including phytoplankton and reef communities are likely to have been badly affected.

Most researchers agree this type of event is very unlikely. For a supernova to do real damage on Earth, it probably has to occur at a distance of less than about fifty light years. All such nearby stars are of sufficiently low mass (less than about ten times the mass of the Sun) that they will very likely lose enough of their mass in their red giant phase and turn into white dwarf stars without an explosion. Spica, the brightest star in Virgo, has a mass of about ten times the Sun, and will probably explode as a supernova in several million years, but it is 260 light years away.

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