Live radioisotopes as signatures of nearby supernovae

Nearby (less than or similar to1 kpc) supernovae were almost certainly common in earth's geological history. Such events allow the direct study of their freshly synthesized live radioisotopes, opening new windows onto supernovae. Very close supernovae (within a few tens of pc) may deposit radioisotopes directly on the earth. Recent high-sensitivity accelerator mass spectrometry measurements of deep-ocean samples find live Fe-60 at levels that greatly exceed background, suggesting an explosion occurred within 30 pc during the last 5 Myr. Somewhat more distant-but also more frequent-supernovae leave observable signatures of radioisotopes whose decay includes gamma-ray line emission. In particular, a large, old supernova remnant was recently discovered at similar to100 pc, and appears to contain Al-26. If confirmed, this would be the first detection of Al-26 in a single remnant, and would be a new probe of supernova nucleosynthesis and astrophysics. (C) 2003 Elsevier B.V. All rights reserved.