Jupiter's moon Ganymede, our solar system's biggest moon, may possess a layered "club sandwich" interior makeup of ice and water in which exotic marine organisms might find it possible to exist, scientists say.
The new theoretical model is at odds with former assumption the moon harbored a single ocean layer sandwiched between single layers of frozen ice above and below.
"Ganymede's ocean might be organized like a Dagwood sandwich," says Steve Vance at NASA's Jet Propulsion Laboratory in Pasadena, Calif., a reference to the well-known many-layered sandwich in the comic strip "Blondie."
First put forward as a theory of Ganymede's internal structure last year, more studies by Vance and others have yielded new evidence for a "club sandwich" interior model.
If it's correct, it would give support to the possibility of primitive life having arising on the frigid moon.
Before the new model, the rocky bottom of what was assumed to be Ganymede's single ocean layer was thought to be covered with ice, which would be a barrier to an emergence of life.
In the multi-layer sandwich model, the layer immediately atop the rocky bottom could consist of salty water, they researchers say.
"This is good news for Ganymede," says Vance. "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."
That's significant because where regions where rock and water can interact are considered important factors in the development of life, scientists say.
Five moons orbiting planets in our solar system -- Ganymede, Callisto and Europa at Jupiter and Enceladus and Titan at Saturn -- are believed to have vast oceans lurking beneath their icy crusts.
In 1995, NASA's sent its Galileo mission to fly by the giant Ganymede -- the moon is larger than the planet Mercury -- confirming the existence of its ocean and determining it was several hundred miles deep.
While the "club sandwich" model of Ganymede remains only a theory at the moment, The European Space Agency is working on a mission dubbed the JUpiter ICy moons Explorer, or JUICE, intended to reach and study Ganymede, Callisto and Europa by the 2030s.
Among the instruments aboard the spacecraft when it launches in 2022 will be three developed by JPL and NASA.
