On April 13, 2023, the European Space Agency is scheduled to launch a rocket carrying a spacecraft called Jupiter Icy Moons Explorer (JUICE), destined for Jupiter; followed by NASA's robotic spacecraft Europa Clipper, launching in October 2024.
But the real interest for both: three of Jupiter's moons — Europa, Ganymede and Callisto. All three almost certainly possess underground oceans of liquid water," says Purdue University Professor of Planetary Science Dr. Mike Sori in The Conversation.
Europa’s ocean alone has more than double the water of all of Earth’s oceans combined
These three moons "have chilly surfaces that are hundreds of degrees below zero," says Sori. "At these temperatures, ice behaves like solid rock. But just like Earth, the deeper underground you go on these moons, the hotter it gets. Go down far enough and you eventually reach the temperature where ice, warmed by a volcanic sea floor, melts into water."
How do we know? "When these moons travel through Jupiter’s magnetic field, they generate a secondary, smaller magnetic field that signals to researchers the presence of an underground ocean. Using this technique, planetary scientists have been able to show that the three moons contain underground oceans."
What about extraterrestrial life?
Liquid water is an important piece of what makes for a habitable world, but far from the only requirement for life. "Life also needs energy and certain chemical compounds in addition to water to flourish. On Europa, for example, the liquid water ocean overlays a rocky interior. That rocky seafloor could provide energy and chemicals through underwater volcanoes that could make Europa’s ocean habitable.
Magnetometers will also be on both missions. These tools will give scientists the opportunity to study the secondary magnetic fields produced by the interaction of conductive oceans with Jupiter’s field in great detail and will hopefully give researchers clues to salinity and volumes of the oceans.
"Scientists will also observe small variations in the moons’ gravitational pulls by tracking subtle movements in both spacecrafts’ orbits. That could help determine if Europa’s seafloor has volcanoes that provide the needed energy and chemistry for the ocean to support life."