Ganymede is Jupiter’s largest moon; in fact it’s the solar system’s biggest moon. Now members of the Icy Worlds team at NASA’s Jet Propulsion Laboratory (JPL) think that the giant moon, which is even larger than the planet Mercury, may have several layers of ice and liquid oceans piled atop each other, much like a club or other type of stacked sandwich.
The JPL scientists based their findings on computer models of Ganymede’s makeup.
The research also revealed that the icy moon may have hosted primitive life.
They drew attention to areas of the Jovian moon where water and rock intermingle and said those interactions are important for the development of life. The researchers pointed out that life on our own planet may have also gotten its start in a similar way.
Some scientists propose that about 3.6 billion years ago, key life-giving elements contained within material that originated deep beneath Earth’s surface bubbled out of hydrothermal ocean vents and eventually developed into our planet’s earliest life forms.
Until these recent findings, it was thought that the rocky sea bottom of Ganymede was covered with ice instead of liquid, which is something that could prevent the development of life. The computer models the scientists produced for their research also led them to believe that the first layer atop the moon’s core might be salty water.
“This is good news for Ganymede,” said JPL’s Steve Vance, who also led the study. “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.”
Models of Ganymede’s oceans produced in the past led scientists to assume that salt had little effect of a liquid’s properties with pressure. But the JPL team conducted laboratory tests that showed the density of liquids under the same harsh conditions inside of Ganymede were increased with salt.
While some may find it odd that the ocean could be made to be denser with the addition of salt, the researchers suggested an experiment that can be tried at home that will show how this is possible. Simply add some regular table salt to a glass of water. You should be able to notice that instead of increasing the volume of liquid within the glass, it shrinks and becomes denser. This is, according to the scientists, because the salt ions attract water molecules.
As the JPL scientists progressed through their computer models they noticed that things got a little more complicated when they took the different forms or phases of ice into consideration.
The cubes of ice you add to your drink to make it colder is referred to as something called “Ice Ih.” It’s lighter than liquid water and is the least dense form of ice.
But you start adding in more pressure and the structure of the ice crystals become much more compact.
Incredibly high pressure, such as what is thought to be found in the deep oceans of Ganymede, produces ice that is so dense that it can actually drop to the bottom of the ocean. Study scientists believe the densest form of ice on the Jovian moon is “Ice VI”.
The team added these processes to their computer model and came up with an ocean sandwiched between up to three ice layers that cover the rocky seafloor of Ganymede. The lightest ice makes up the top layer and the bottom layer consists of the saltiest liquid.
The JPL team said that their findings can also be applied to the study of exoplanets or planets beyond our solar system. Some have proposed that a number of the rocky exoplanets that are more massive than Earth – Super-Earths – are also covered in oceans.
Vance and his colleagues think that scientists conducting laboratory experiments with models similar or even more complex than those they used in their research could help determine whether or not life could exist on these alien “water worlds”.