Number 76 (Story #3), April 17, 1992 by Phillip F. Schewe and Ben Stein TITAN'S ATMOSPHERE may have come from a comet. Kevin Zahnle and his colleagues at the NASA Ames Research Center suggest that in the early stages of the solar system comets from beyond Uranus may have struck Saturn's moon Titan, which had enough gravity to retain the material. Smaller moons, or those farther in, such as Jupiter's moon Ganymede and Callisto, may not have been able to capture or keep the comet debris. (New Scientist, 11 April 1992.)