Enceladus, a moon of Saturn, may be home to an ocean the size of Lake Superior. This body of water, hidden beneath the surface of the frozen satellite, may now be considered one of the most likely places in the solar system to find alien life. 

Cassini, a spacecraft first launched in 1997 to study Saturn, along with its rings and moons, does not have the capability to directly detect water. For years, the craft has provided pictures and data about dark lines and features seen on the surface of Enceladus. Organic material in the structures is mixed with ice.  

Astronomers were able to make precise measurements of the gravitational field of the moon, revealing the density of material beneath the surface. During three flybys of Enceladus between 2010 and 2012, radio signals from Earth were sent to the spacecraft and back to our home planet. By measuring tiny changes in the signal, researchers were able to measure the gravitational influence of regions of the moon on Cassini. 

The southern pole of Enceladus shows a large depression in the ice. This would suggest gravitational forces on the craft would be slightly lower over the northern pole than the south. Cassini discovered the area does exhibit less of a tug than other regions of the moon, but the difference was not as great as had been predicted. 

"So, you say, 'Aha! This is compensated at depth,'" David Stevenson of the California Institute of Technology and author of the article announcing the results, said. 

Frozen on the outside, due to its great distance from the Sun and lack of atmosphere, the moon is warmed by tidal forces. Gravity from Saturn and another moon, Dione, pulls on the surface of Enceladus, stretching and warping its surface. This creates heating in the crust and water, caused by friction. This could mean the water is warmed enough to be liquid. 

Just 300 miles in diameter, the fourth-largest moon of Saturn may be even more likely than Mars or Titan to house alien life. 

In 2005, the Cassini spacecraft detected geysers of ice on the Saturnian moon, suggesting the satellite might house a large ocean. This new finding confirmed those earlier theories. 

If confirmed, "there is a large, possibly regional ocean about [30 miles] below the surface of the south pole. This then provides one possible story to explain why water is gushing out of these fractures we see at the south pole," Stevenson said. 

Discovery of the subsurface ocean on Enceladus was detailed in the journal Science.