| We investigate the mechanism by which supernova ejecta can penetrate the solar system, and in particular, directly deposit live radioactivities on Earth. This study is motivated by the discovery of live undersea 60Fe from an event 2.8 Myr ago. The 60Fe signal is consistent with a nearby supernova explosion---occurring within a few tens of parsecs from the solar system. We present the first numerical hydrodynamic simulation of the interaction between a supernova blast and the solar wind, using the FLASH code. We find that the supernova ejecta can penetrate the solar system within the orbit of the Earth if the supernova explosion is within 10pc of the Sun. Since 10 pc marks the nominal "kill radius" within which biosphere damage is severe and could lead to species extinction events, the absence of paleontological evidence of such an extinction coeval with the 60Fe deposition leads us to consider a more subtle mechanism of ejecta delivery. There exists evidence that the vast majority of heavy elements in a supernova remnant may be depleted onto grains, hence they can be considered as charged particles which do not participate in the plasma dynamics of the interaction of the supernova plasma and the solar wind. We examine the motion of these charged particles as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation and gravitational field. We find that given the large incoming velocities of the charged grains, they suffer little or no deflection within the solar system. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability, and the dust capture onto the Earth should have a geometric cross section. |
