In order to ask a question such as this, and ultimately answer it, one needs to first understand what life is, and then analyze the degree to which a celestial body is capable of sustaining this life. And what are the requirements for life as we know it? In the most basic sense: water, an atmosphere, and a source of energy. The interesting bit here is that Enceladus only fits into two of these categories (it has water and an atmosphere). However, this does not necessarily mean that life cannot survive. After all, the lifeforms that exist in the deepest parts of our ocean are a prime example of living beings thriving in unexpected places. And it seems that similar oceans flow under the icy covering of Enceladus.
Enceladus is one of Saturn’s small moons (it’s about the size of Wyoming). Interestingly, it is also one of the brightest objects in our Solar System. This is a world that has a temperature of -201 degrees Celsius (-329 Fahrenheit). Meaning, the moon is completely frozen over. Could life exist on this frozen moon? Apparently, the answer is yes (of course, scientists don’t expect this life to be a species of gigantic super aliens that want to enslave humanity…just bacteria).
Although the outer crust of the planet is frozen ice, there are vast plumes of water that shoot out from the surface (sometimes containing 20000 liters or more). In fact, Enceladus has MASSIVE underground (or "underice") oceans. Though this planet is tiny compared to Earth (picture a marble compared to a soccer ball), it contains 3/4 the amount of water that the Earth does. Ultimately, these massive under-ice oceans are what power such huge outbursts of water.
Scientists monitoring Enceladus have found that these plumes are constantly between 59 and 212 degrees Fahrenheit (15 and 100 degrees Celsius). Since the temperature of this water is more agreeable with life as we know it, there are hopes that it could contain bacteria. And considering that Enceladus has more than 5 different terrain types (most orbiting bodies have 2 or 3) it vastly increases the probability of alien life.
So although this moon orbits 1billion miles from the Sun, it still seems to have "livable" conditions. Notably, varying amounts of organic compounds exist in Enceladus’ oceans. We know this because, with every outburst of water, satellites register the building blocks of life in the surrounding space. Additionally, although the atmosphere of Enceladus is very thin, it contains the essentials for life (potent amounts of water vapor, carbon dioxide, and nitrogen gas have been found). In fact, what led scientists to believe that bacteria could exist in such an environment in the first place was the presence of carbon dioxide, which is a byproduct of many forms of bacteria.
In October of 1997 NASA launched Cassini. This craft, which was designed to investigate Saturn, is now investigating Enceladus. The aim of the newly named "Cassini Solstice Mission" is to fly the craft directly through one of the plumes of water on Enceladus and obtain a sample of the contents. This shouldn’t be too difficult, as these plumes can reach 1.2 miles (2km). Now the one type of bacteria scientists believe could live there would be "Cupriavidas metallidurans." This variation of bacteria resides here on Earth too. It lives in gold chloride, also known as "liquid gold." They can survive incredible temperatures, ranging from -150 degrees Celsius to well over 200 degrees Celsius. This bacteria would not need any form of light to survive (and considering that the sun is 1billion miles away, this is a very good thing).
In simple terms—Enceladus seems to be the reason why scientists came up with the term "Astrobiology." And with the fascinating yet strange "hotspots" at the Southern tip of the moon (which displays near Earth like temperatures) who knows what NASA may find?