From the volatile landscape of Io, pockmarked by eons of volcanic activity, to Ganymede’s saltwater oceans sandwiched between hundreds of miles of ice and rock, Jupiter’s so-called Galilean moons are uniquely diverse and act like a miniature solar system.
“Jupiter is an archetype of gas giants,” says Werner Magnes from the Space Research Institute at the Austrian Academy of Sciences in Graz, Austria. “It’s a kind of mini-solar system, which means Jupiter acts like a star in a minisystem with its moons acting like planets.”
That’s why the European Space Agency chose the distant gas giant’s icy moons as the target of its next big scientific mission. The 19-member group opted this month to send a spacecraft to explore and investigate the satellites, which are located some 500 million miles away from Earth. The plan is to launch the Jupiter Icy Moons Explorer, or JUICE, in 2022.
“No one has ever orbited one of these moons, which means it has never been studied in the high level of detail that JUICE will allow,” said Fabio Favata, the man responsible for planning all of the missions in ESA’s science program.
The mission will study the moons’ potential habitability and address two big questions: What are the conditions for planet formation and the emergence of life, and how does the solar system work?
Once JUICE reaches the Jovian system in 2030, the spacecraft will zip past Callisto and twice fly by Europa, measuring the thickness of their icy crusts and identifying potential landing sites for future explorations.
Europa, Callisto and Ganymede are all believed to have subsurface oceans. Ganymede in particular is the only moon in the solar system known to generate its own magnetic field, and JUICE will enter orbit around it in 2032. The craft will then continuously observe Jupiter’s atmosphere and magnetosphere and beam back data on the interaction of the Galilean moons and the gas giant.
"We won't be able to literally look into the ocean, that much is clear," Favata said. "But we will be able to do all sorts of measurements ... that allow you to really understand the worlds below the icy crust."
To make this possible, scientists from around the world are scrambling to fashion the most effective tools for gathering data remotely and relaying it back to Earth.
One such instrument is the craft's magnetometer. Designed by Magnes’ team at the Space Research Institute in Austria, it is outfitted with high-tech sensors for measuring the direction and intensity of a body’s magnetic fields via a process similar to radar.
A decision regarding which instruments will make the cut and be included in the final payload will be made this fall, Favata said. All in all, he added, a craft as large and complex as JUICE will take six to eight years to put together.
The JUICE mission was selected over two other candidates by ESA’s Space Science Advisory Committee for the next big scientific mission, according to information provided by the agency. One was a proposal for a new gravitational wave observatory, while the other was an advanced telescope for high-energy astrophysics.
"When you make such a big decision, it's hard to identify a single factor," Favata said about the reasoning behind ESA's choice of the JUICE mission. "You could call it an embarrassment of riches, because all three could have been done. All three were excellent projects."