Solar Energetic Particle and Galactic Radiation Hazards in the Past, Present, and Future (Invited Presentation)

Solar energetic particles (SEPs) and Galactic Cosmic Rays (GCRs) constitute significant hazards to humans and hardware in space. Measurements of the radioactive isotopes ¹⁰Be in ice cores and ¹⁴C in tree rings show that the GCR intensity was ~50% greater during the Maunder minimum than at present. In addition, polar ice-core data for ¹⁴C, ¹⁰Be, and ³⁶Cl show that there have been at least three instances in the past when nuclear reactions of SEP ions in Earth’s atmosphere produced excesses of these rare isotopes well above those due to the more steady cosmic ray background. The largest of these events (in 775 AD) produced at least 5 times the ¹⁴C (in the span of a few months or less) than was produced in the February1956 SEP event, the largest ground-level SEP event of the last 80 years. This talk will relate GCR and SEP measurements during the last few solar cycles to those from the last few thousand years, and discuss the implications for future human space exploration.