Enceladus is a medium-size moon of Saturn, with a diameter of about 500 km. Its surface temperature is quite chilly, ranging between 32.9 K (-240 degrees Celsius) and 145 K (-128 degrees Celsius); this is partially because of its distance from the Sun, and also because of its highly reflective surface. The entire moon is coated in fresh ice, so it reflects a lot of the sunlight that reaches it. This helps make it cold, and also makes it one of the brightest worlds in the solar system. Despite its small size and its frigid surface temperatures, Enceladus seems to show signs of ongoing geological activity, due to the fact that its orbital resonance with Dione (another of Saturn’s moons) causes tidal heating.
One of the most fascinating things about Enceladus is that it is believed to have a global subsurface ocean of water beneath its coating of ice. Thanks to tidal heating, Enceladus spews geysers of its ocean material from near its South Pole. The Cassini spacecraft found that these geysers contain mostly water vapor, along with traces of nitrogen, methane, and carbon dioxide. The geysers reach hundreds of miles into space, and the released material makes up most of Saturn’s E ring.
The presence of liquid water and other compounds have led many to speculate/wonder if Enceladus is capable of sustaining some form of life in its ocean. Programs such as the Breakthrough Initiatives and other proposed missions such as the Enceladus Life Finder seek to find whether life does exist somewhere on Enceladus.