  About 4.6 billion years ago, some event disturbed a cloud of gas and dust,
triggering the gravitational collapse that led to the formation of the solar
system. A core-collapse supernova, whose shock wave is capable of compressing
such a cloud, is an obvious candidate for the initiating event. This hypothesis
can be tested because supernovae also produce telltale patterns of short-lived
radionuclides, which would be preserved today as isotopic anomalies. Previous
studies of the forensic evidence have been inconclusive, finding a pattern of
isotopes differing from that produced in conventional supernova models. Here we
argue that these difficulties either do not arise or are mitigated if the
initiating supernova was a special type, low in mass and explosion energy. Key
to our conclusion is the demonstration that short-lived Be-10 can be readily
synthesized in such supernovae by neutrino interactions, while anomalies in
stable isotopes are suppressed.
