Solar system exposure to supernova γ radiation

Abstract

Planetary habitability may be affected by exposure to γ radiation from supernovae (SNe). Records of Earth history during the late Quaternary Period (40 000 years to present) allow testing for specific SN γ radiation effects. SNe include Type Ia white dwarf explosions, Type Ib, c and II core collapses, and many γ burst objects. Surveys of galactic SNe remnants offer a nearly complete accounting for this time and including SN distances and ages. Terrestrial changes in records of the cosmogenic isotope 14C are here compared to SN-predicted changes. SN γ emission occurs mainly within 3 years; average per-event total emissions of 4 × 1049 erg are used for comparison of close events There are 18 SNe ≤ 1.5 kpc, and brief 14C anomalies are reported for eight of the closest. Four are notable (BP is year before 1950 CE): the older Vela SNR and an abrupt 30‰ del 14C rise at 12 740 BP; S165 and a 20‰ rise at 7431 BP; Vela Jr. and a 14‰ rise at 2765 BP; and HB9 and a 9‰ rise at 5372 BP. Rapid-increase anomalies in 14C production have been attributed to cosmic rays from exceptionally large solar flares. However, the proximity and ages of these SNe, the probable size and duration of their γ emissions, the predicted effects on 14C, and the agreement with 14C records together support SNe causation. Also, the supposed solar-caused 14C anomalies at CE 774 and 993 may instead have been caused by the SNe associated with the G190.9-2.2 and G347.3-00.5 remnants. Both are of appropriate age and distance.

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