Cover: This special issue of Astrobiology is a collection of articles that, together, presents an up-to-the-minute assessment of the meaning and significance of Cassini's discoveries at Enceladus and maps out new directions for future exploration of this captivating world. This natural color view of Saturn during its southern summer, on March 16, 2006, was created by combining images taken through the red, green, and blue spectral filters with Cassini's wide-angle camera. The solar phase angle is 102 degrees. The image scale is ∼120 km/pixel. The rings, which are not spatially resolved in the vertical direction, are seen edge-on. Their shadows are draped on the blue northern (winter) hemisphere. Enceladus, 504 km across, hugs the ringplane right of center.

Despite Enceladus' diminutive size, it is home to the Cassini mission's most profound discovery. Within the moon lies a global ocean of salty liquid water, with traces of organic compounds and evidence of hydrothermal activity on its seafloor, that erupts at the south pole in a spectacular array of over 100 geysers through deep, prominent fractures in its overlying ice shell. Enceladus' geysering activity makes its watery reservoir the most accessible and promising habitable zone in the Solar System for future astrobiological study.

Image credit: NASA/JPL-Caltech/Space Science Institute