Can 1957 cold-fusion explain 1989 cold-fusion?

The possibility that muon-catalyzed nuclear fusion at ambient temperature takes place in deuterated metals is analyzed theoretically. It is suggested that the muon-catalyzed deuterium-deuterium (dd) or deuterium-tritium (dt) fusion rate, experimentally observed in liquid deuterium, increases in a PdD crystal. The main reason is that, in the palladium crystal matrix, deuterium diffuses in ionic (d+), rather than molecular (D2), form, thereby favoring the rate of (d$\mu$d)+ formation. The slightly enhanced deuterium density and the possibly reduced muon sticking probability (compared to liquid hydrogen) point to an increase of the fusion-rate, unfortunately counterbalanced by the probability of $\mu^-$ capture by the Pd nucleus, whose value should be evaluated by a dedicated experiment. If this mechanism were possible, we advance the hypothesis that 1989 cold fusion might have been randomly triggered by cosmic muons: an order-of-magnitude analysis shows that, under special conditions, a mW power per $\mu^-$ might be produced. Moreover, recent experimental results showing that neutrons can sustain deuterium fusion in out-of-equilibrium conditions might explain the remaining power generation. However, reliable quantitative figures are difficult to obtain theoretically, and an experiment is suggested, to be conducted at muon-beam sources, to verify or invalidate this idea.