Even by the diverse standards of Saturn's satellites, Enceladus was an outlier. Its icy surface was as white and bright as fresh snow, and whereas the other airless moons were heavily pocked with craters, Enceladus was mantled in places with extensive plains of smooth, uncratered terrain, a clear sign of past internally driven geologic activity.

Scientists tend to come in two stripes: those who have tremendous appetite and aptitude for the details, and those who illuminate the big picture. Sagan was definitely in the latter category, and he was profoundly good at it. He made connections that others did not have the intellectual breadth or courage to make.

'Carl Sagan: A Life,' though a riveting tale, tells as much about the all-too-human feelings of jealousy and resentment as it does about the individual who inspired them.

Carolyn Porco Quotes