Comets have not only blazed across the celestial vault throughout human history, they have embellished the night sky since the Earth itself formed some 4.5 billion years ago. Comets were among the first-born solid bodies in the solar system, and their frozen nuclei tell of the primordial chemistry and chaos that ultimately resulted in the formation of the planets, the evolution of life and us. For all this, however, comets have long been celestial oddities: they baffled our distant ancestors,...