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New 'club sandwich' model of Ganymede has implications for life

Ganymede club sandwich
Ganymede club sandwich
NASA/JPL

NASA’s Jet Propulsion Laboratory announced on Thursday that recent computer modeling suggests that Jupiter’s moon Ganymede might have several layers of ice and liquid water, sort of like a “club sandwich.” Before scientists thought that Ganymede might have a liquid ocean sandwiched between two layers of ice, the lower layer covering the moon’s rocky core. The findings have implications for possible life on Ganymede.

The change that brought about the new model was the assumption that ice is presence in Ganymede’s subsurface oceans. Salt makes water denser by attracting the h20 molecules to salt ions. The denser water tends to sink to the surface of Ganymede’s rocky core.

Ice can be denser depending on how much pressure it exerted on it. The least dense ice can be thought of as being like the ice that floats in a drink. Ganymede has an outer layer of ice, an inner layer of ice, and a middle layer that is more like slush than ice.

NASA describes the processes that may have created this multilayer of alternating ice and water thus:

“By modeling these processes using computers, the team came up with an ocean sandwiched between up to three ice layers, in addition to the rocky seafloor. The lightest ice is on top, and the saltiest liquid is heavy enough to sink to the bottom. What's more, the results demonstrate a possible bizarre phenomenon that causes the oceans to ‘snow upwards.’ As the oceans churn and cold plumes snake around, ice in the uppermost ocean layer, called "Ice III," could form in the seawater. When ice forms, salts precipitate out. The heavier salts would thus fall downward, and the lighter ice, or "snow," would float upward. This ‘snow’ melts again before reaching the top of the ocean, possibly leaving slush in the middle of the moon sandwich.”

The reason that this new model has implications for life on Ganymede stems from the fact that liquid water exists on top of the surface of the rocky core, The theory is that places where the ocean floor and the water meet and interact are important for the evolution of life. It is thought that life on Earth started when organic compounds began forming into life forms, heated by vents at the bottom of the ocean. Clearly this could not have happened if there had been a layer of ice between the water and the ocean floor.

This new model is certainly not proof that there is life on Ganymede. But Ganymede does join the number of outer planet moons such as Europa and Titan that might have life. The only way to be sure is to take a closer look.