NASA's Cassini spacecraft has discovered signs of what appears to be a large body of water on Enceladus, an icy moon orbiting Saturn. The findings were reported in the journal Science on Thursday.
The Washington Post's Joel Achenbach breaks down the reasons why scientists believe this is actually water: gravity, shape, and plumes. Enceladus appears to have a gravitational asymmetry, with the moon's pull slightly different in the area around the south pole, and calculations make it appear that this is due to liquid water, which is denser than ice. Also at the south pole, there's a depression that bolsters the hypothesis of denser water below the surface. Then there are plumes of water vapor spewing from the south pole, which could be caused by a deep ocean pushing water up through the cracks in the moon's crust.
The report also suggests that Enceladus' sea has a rocky floor, which, The Post adds, "is significant because the contact between liquid water and rock creates the potential for the kind of interesting chemistry that gets astrobiologists excited."
According to NASA, the ocean could be six miles deep, have roughly the same volume of water as Lake Superior, and lie beneath an ice shell 19 to 25 miles thick. Read more at Science.