An ocean of liquid water may lurk under the icy crust of Enceladus, one of Saturn’s moons. The new NASA observations make the satellite one of the most likely places in our solar system to be harboring extraterrestrial microbial life.
Locations in the solar system with liquid water are considered candidates for alien life because all life-forms on Earth require H2O to survive. Astrobiologists—scientists interested in life beyond Earth—have had their eye on Enceladus ever since researchers discovered plumes of salty water vapor and ice containing organic molecules jetting from the moon’s south pole in 2005.
The new evidence comes from measurements of tiny gravitational fluctuations at the moon’s south pole, which are most easily explained by the greater density—and gravitational pull—of liquid water compared to ice. (Water is denser than ice, which is why ice cubes float.) The shape of the moon’s gravity field strongly suggests that the mysterious icy plumes discovered in 2005 originate from a 6-mile-deep ocean under a 19- to 25-mile-deep layer of surface ice.
As exciting as this finding is, we won’t be looking for life on Enceladus in the near future. Another icy moon suspected to have a subsurface ocean, Jupiter’s Europa, is first in line for limited space exploration funding. If Europa does have an ocean, scientists believe it has a rocky seafloor with nutrients that could sustain microbial life.