A safe distance from a supernova explosion is typically defined as thirty light-years
Two sources discuss near-Earth supernovae and atmospheric protection, but insufficient evidence is available to establish thirty light-years as the typically defined safe distance.
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Earth’s atmosphere protects the biosphere from nearby supernovae | Communications Earth & Environment. https://www.nature.com/articles/s43247-024-01490-9
Earth’s atmosphere protects the biosphere from nearby supernovae | Communications Earth & Environment Download PDF ### Subjects - Atmospheric chemistry - Environmental chemistry - Space physics ## Abstract Geological evidence indicates that a supernova within 100 parsecs of Earth occurs around once per million years. Such nearby supernovas can produce an intense gamma-ray burst and a 100-fold increase of cosmic rays, lasting several centuries. We find that the effect of a short burst of gamma rays is small since they are strongly attenuated before reaching the lower stratosphere. Intense cosmic radiation affects stratospheric ozone but, due to compensating effects in catalytic chemical cycles, ozone depletion is moderate and comparable to that from current anthropogenic emissions. This also holds for the low-oxygen atmosphere during early evolution of terrestrial life. We estimate the increase in aerosol and clouds from a 100-fold increase of cosmic rays exerts a radiative forcing comparable in magnitude but opposite in sign to current anthropogenic climate forcing. We conclude that Earth’s atmosphere is effective at shielding the biosphere from nearby supernovae. ### Eviden
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Near-Earth supernova - Wikipedia. https://en.wikipedia.org/wiki/Near-Earth_supernova
Near-Earth supernova The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova. It is located about 6,500 light-years from the Earth. A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth, less than roughly 10 to 300 parsecs [33 to 978 light-years] away, to have noticeable effects on its biosphere. An estimated 20 supernova explosions have happened within 300 pc of the Earth over the last 300 thousand years. Type II supernova explosions are expected to occur in active star-forming regions, with 12 such OB associations being located within 650 pc of the Earth. At present, there are up to 14 near-Earth supernova candidates within 300 pc. ## Effects on Earth Estimates for the rate of supernova explosions are highly uncertain. An example is that on average, one supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. Gamma rays are responsible for most of the adverse effects that a supernova may have on a life-harboring terrestrial planet. In Earth's case, gamma rays induce radiolysis of diatomic N2 and O2 in the upper atmosphere, converting molecular nitrogen and
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