In this Photograph, taken by the Cassini spacecraft in June 2006, the brilliant silhouette of Titan, Saturn’s largest moon, is visually bisected by Saturn’s elongated rings. The moon Enceladus transits the scene at the bottom right. Enceladus was 2.4 million miles away from Cassini, and Titan was 3.3 million miles away. Astrobiologists believe that both moons may be habitable with the right supplies. Surviving on Titan would require only an oxygen mask and warm clothing, as well as the willingness to live through days that are equivalent to 16 Earth days. In contrast, the icy, geyser-ridden moon Enceladus is so cold that the warmest areas, at the south pole, reach only minus 120 degrees Fahrenheit.
—Adapted from The Planets: Photographs From the Archives of nasa, by Nirmala Nataraj, with a preface by Bill Nye