The early twentieth century saw the replacement of the Nebular Hypothesis with the Chamberlin-Moulton theory that the solar system resulted from the encounter of the Sun with a passing star. Fruitful Encounters follows the eventual refutation of the encounter theory and the subsequent revival of a modernized Nebular Hypothesis. Professor Brush also discusses the role of findings from the Apollo space program, especially the analysis of lunar samples, culminating in the establishment of the "giant impact" theory of the Moon's origin in the 1980s.