It’s only a seltzer moon

Plumes from Saturn’s Enceladus may have carbonated source

Eau my! Things could be really popping inside Saturn’s moon Enceladus. A fizzy ocean, similar in carbonation to Perrier, may feed the plumes of water vapor, gas and ice that erupt from the south pole of the moon, a new model suggests.

A fizzy, interior ocean similar to Perrier may feed jets spraying from the south polar region of Saturn’s moon Enceladus. Bubbles in seawater travel through a passage in the icy crust to feed a geyser, as shown in the illustration above. The expelled seawater then flows back down to the subsurface ocean through cracks in the ice. SSI, JPL/NASA

Since 2005, when the Cassini spacecraft first observed icy plumes spewing from the south pole of Enceladus (SN: 5/6/06, p. 282), researchers have speculated that an ocean may lie buried tens of kilometers beneath the moon’s fractured, icy surface. Now, Cassini scientist Dennis Matson of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues propose adding a bit of effervescence to the watery hypothesis. Circulating, bubbly seawater containing 1 or 2 percent dissolved carbon dioxide and other gases could supply water, gas, dust and heat to Enceladus’ polar plumes, the researchers say. It can also explain why some of the ice grains expelled by the plumes carry sodium and potassium salts.

Noncarbonated seawater circulating from the moon’s solid core to the surface would stall rather than seep though cracks in the ice because seawater is denser than the icy carapace. If the seawater were fizzy, however, gas bubbles would form in the liquid, reducing the ocean’s density. Once the seawater became less dense than the ice, the water could rise to within 10 to 15 meters of the frigid surface. That’s close enough to fill chambers in the icy crust with water that feeds the south polar plumes.

In addition, as the bubbles popped they would spray the plume chambers with tiny droplets containing dissolved salts from the seawater. Those droplets would emerge from the plumes as salty grains like those that have been observed by Cassini (SN: 8/30/08, p. 10). The bubbly water would also warm large areas of the icy south polar crust, Matson notes.

After the water transferred its heat and grew colder, the bubbles would dissolve and the water would once again become denser than the surface ice. The liquid would sink back through the cracks and rejoin the rest of the subsurface ocean.

Matson sketched the findings during a press briefing October 4 at the American Astronomical Society’s Division for Planetary Sciences annual meeting in Pasadena and presented further details during his scientific presentation October 5.

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