Year in review: Ocean may power Enceladus’ geysers

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The case for a saltwater ocean — and a potentially habitable environment — beneath the icy crust of Saturn’s moon Enceladus keeps getting stronger.

Enceladus has been dribbling hints about a subsurface sea since the Cassini spacecraft first visited the moon in 2005. Salty ice geysers erupt through cracks in the south polar ice sheet. Heat wells up through the fissures, presumably from a deep, warm reservoir. But all evidence for an interior sea had been limited to surface observations — until this year.

In April, Luciano Iess of Sapienza University of Rome and colleagues used Cassini data to map an ocean hiding under the moon’s south pole (SN: 5/3/14, p. 11). The sea holds about as much water as Lake Superior.

Iess’ data couldn’t pinpoint what powers the surface geysers. Three months later, however, Carolyn Porco of the Space Science Institute in Boulder, Colo., and colleagues found evidence connecting the fountains to an underground water supply (SN: 9/6/14, p. 15). Using Cassini images and maps, Porco found that warm spots at the base of each geyser are too small to power the jets, so the spray couldn’t originate at the surface. Most likely, Saturn’s gravity repeatedly opens and closes the fissures, allowing water and heat to escape from the interior and vent into space.

The findings suggest that water jetting out of Enceladus probably comes from a warm, briny, subsurface sea atop a rocky core. There’s no evidence for life, but many of the ingredients seem in place.