NASA’s Galileo spacecraft flew by Ganymede in the 1990s and confirmed the presence of an interior ocean. It also found evidence for salty water which may be from salt known as magnesium sulfate.
A team of scientists performed computer modeling of Ganymede’s ocean, taking into account, for the first time, how salt increases the density of liquids under the type of extreme conditions present inside Ganymede. Earlier research suggested just a regular “sandwich” set-up in which there is ice at the surface, a layer of liquid water in the middle, and another layer of ice on the bottom. This new study, however, suggests there may be more than these three layers.
An astrobiologist at NASA’s Jet Propulsion Laboratory in California, Steve Vann, said the new study reveals the arrangement may be more like the following:
- a layer of ice on the moon’s surface (on the top);
- a layer of water beneath that;
- a second layer of ice;
- another layer of water underneath that;
- a third layer of ice; and
- a final layer of water at the bottom – above the rocky seafloor.
“That would make it the largest club sandwich in the solar system,” Vann said in a telephone interview. “I suppose I’m also a fan of club sandwiches. My fiancée points out that I order them every time we go out to eat.”
Ganymede boasts a lot of water, perhaps 25 times the volume of the Earth’s oceans. Its oceans are estimated to be about 500 miles (800 km) deep.
With sufficient salt, Ganymede’s liquid water could become so dense that it sinks to the very bottom, according to researchers. That means water could be lapping on top of rock, a situation that may foster conditions suitable for the development of microbial life.
Some scientists think life first formed on Earth in building thermal vents on the ocean floor.
“Our understanding of how life came about on Earth involves the interaction between water and rock. This (research) provides a strong possibility for those kinds of interactions to take place on Ganymede,” added Vance, whose study was published in the journal Planetary and Space Science.
“We’re providing a more realistic view into ocean structure in Ganymede’s interior. We’re showing that the salinity has a tangible effect on the ocean,” Vance said.