NASA believes that the most likely places to find life beyond Earth could be right next door — at least in space terms. They have new evidence to suggest that Jupiter's moon Europa and Saturn's moon Enceladus both contain vital requirements that would allow for alien life to survive. Enceladus particularly has almost all of the key ingredients for life as we know it.
Enceladus is a frozen ice world, but beneath the inhospitable surface, scientists believe that basic life could be thriving in warm underground seas. NASA's Cassini spacecraft detected an abundance of hydrogen and carbon dioxide in water plumes that rise to the surface through fractures in the surface of the planet.