Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus? Long features dubbed 'tiger stripes'(in blue) are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole.
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
MARYLAND: New evidence has shown that Enceladus, a tiny moon floating just outside Saturn's rings, is home to a vast underground ocean, which is probably fizzy like a soft drink and could be friendly to microbial life.
For years researchers have been debating whether Enceladus, is wet or not, and a close encounter with the moon by NASA's Cassini probe in 2005 kicked off an investigation into its unusual conditions.
"Geophysicists expected this little world to be a lump of ice, cold, dead, and uninteresting," said Dennis Matson of NASA's Jet Propulsion Laboratory. "Boy, were we surprised!"
A precociously active moon
Cassini found the little moon busily puffing plumes of water vapor, icy particles, and organic compounds out through fissures (now known as ‘tiger stripes’) in its frozen carapace. Mimas, a nearby moon about the same size, was as dead as researchers expected, but Enceladus was precociously active.
Many researchers viewed the icy jets as proof of a large subterranean body of water. Near-surface pockets of liquid water with temperatures near 32o F could explain the watery plumes. But there were problems with this theory. For one thing, where was the salt?
In initial flybys, Cassini's instruments detected carbon, hydrogen, oxygen, nitrogen, and various hydrocarbons in the plume gasses. But there were none of the elements of salt that ocean water should contain.
Resetting the clocks
In 2009 Cassini's cosmic dust analyser located the missing salt – in a surprising place.
"It wasn't in the plume gasses where we'd been looking for it," said Matson. "Instead, sodium and potassium salts and carbonates were locked up in the plumes' icy particles.* And the source of these substances has to be an ocean. Stuff dissolved in an ocean is similar to the contents of these grains."
The latest Cassini observations presented another intriguing discovery: thermal measurements revealed fissures with temperatures as high as -120o Fahrenheit (190 Kelvin). "This discovery resets our clocks!" said Matson. "Temperatures this high have to be volcanic in origin. Heat must be flowing from the interior, enough to melt some of the underground ice, creating an underground waterworks."
Like soft drink spewing from a can
The finding has led the scientists to ponder how contents of an ocean capped by a crust of ice as much as tens of miles thick could reach the surface. "Have you ever been sprayed when you popped the top of a soft drink can?" said Matson.
The model he and his colleagues propose suggests that gasses dissolved in water deep below the surface form bubbles. Since the density of the resulting ‘sparkling water’ is less than that of the ice, the liquid ascends quickly up through the ice to the surface.
