Re: The Extinction Challenge

John Clark (
Fri, 30 Jul 1999 00:18:08 -0400

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Billy Brown <> On July 28, 1999 Wrote:

>A typical supernova would have a total energy output of something like
>10^44 ergs. Applying a little basic geometry, that gives us an energy
>density of 2x10^10 ergs per square meter at a distance of 100 million
>kilometers, which will certainly do a lot of damage. However, at a
>distance of 1 light-year (9x10^12 kilometers), the energy density drops to
>less than one erg per square meter. That isn't even enough energy to
>damage electronics, let alone harm people.

Energy density is not a realistic measure of danger. If the energy is in the form of infrared photons there is no problem, an equal amount of energy in the form of X rays or Gamma rays and there is is a problem. The sinister thing about neutrinos is that there is no way to hide from them and most of the energy in a supernova is released in the form of neutrinos. About 20 neutrino's were detected from the 1987 supernova in a thousand ton tank of water and it was about 200,000 light years away. The numbers I'm using are from memory but I don't think they're too far off. If it were 6 or 7 light years away, that's 30,000 times closer, and the flux would be about a billion times greater. Thus a 200 pound man would receive absorb about 2 million neutrons. A neutrino on the very rare times it hit something would do a lot more damage than the more usual types of radiation like ionizing photons or high speed electrons or protons, it would be almost as damaging as an alpha particle. Usually such a hit would kill the cell it happened in and 2 million dead cells wouldn't be much of a problem for a large animal like a human, but sometimes the cell wouldn't die but become mutated and that's not good. Natural radiation is probably a major cause of cancer and in this case you'd be receiving a massive dose in less than a second.

John K Clark

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