Ganymede's Oceans have Sandwich-Like Stacks of Water and Ice

Jupiter's moon Ganymede might have ice and oceans in the form of a club sandwich, new research suggests.

The club sandwich model for Ganymede was proposed last year. Now, researchers have provided theoretical evidence that supports this idea.

Jupiter's moons; Ganymede, Europa and Callisto and Saturn's Titan and Enceladus have water beneath their icy surfaces. According to astrobiologists, these moons could harbor life.

Previously, other researchers believed that Ganymede couldn't support life because of rocky sea floor had ice. However, the new study suggests that a layer of salty water coats the surface of the sea-floor.  

"Ganymede's ocean might be organized like a Dagwood sandwich," said Steve Vance of NASA's Jet Propulsion Laboratory in Pasadena, Calif. The moon resembles multi-tiered sandwiches of the cartoon character, Blondie.

The club-sandwich arrangement could lead to chemical reactions, and even development of biological organisms, space.com reported.

"This is good news for Ganymede," said Vance in a news release. "Its ocean is huge, with enormous pressures, so it was thought that dense ice had to form at the bottom of the ocean. When we added salts to our models, we came up with liquids dense enough to sink to the sea floor."

Researchers conducted laboratory experiments to show how salt increases density of water hidden beneath Ganymede's surface. Vance and colleagues' model also accounts for the pressure changes that could occur on the moon.

It is a common observation that ice floats on water. But at high pressures, such as those inside Ganymede, ice can become heavier and fall at the bottom of the sea.

In fact, changes in pressure and chemical reactions across the "sandwich layers," could lead to bizarre phenomenon such as snow that falls upwards, researchers said.

The team's sandwich model shows that the ocean on Ganymede has three layers and a rocky seafloor.

"We don't know how long the Dagwood-sandwich structure would exist," said Christophe Sotin of JPL, a co-author of the study. "This structure represents a stable state, but various factors could mean the moon doesn't reach this stable state.

The study is published in the journal Planetary and Space Science.