Why Jupiter’s Moon Ganymede is an Exciting Destination
Ganymede, here we come. A €1 billion mission to place spacecraft in orbit around Jupiter’s largest moon - also the largest in the solar system - has received the green light from the European Space Agency.
Called the Jupiter Icy Moon Explorer, or Juice, the spacecraft will fly past two other Jovian moons - Callisto and Europa - and end its journey in orbit around a third, Ganymede.
While Europa, a water world with the potential to support life, has grabbed more of the limelight over the years, Ganymede,with its own ocean, auroras and oxygen, may have even more to offer, says Emma Bunce, a physicist at the University of Leicester, UK, and a member of the science team behind Juice.
Europa caught the public imagination in the 1980s when images from the Voyager spacecraft suggested water from a liquid ocean might lie beneath a relatively thin, icy crust. The Galileo spacecraft later confirmed the presence of such an ocean.
NASA has tentative plans to visit Europa and at one stage planned to send a Europa orbiter along with Juice. But the agency’s financial woes have intervened and ESA will now go to Jupiter’s moons alone. What will it find?
A little bigger than Mercury, Ganymede is, like Europa, a large, ice-covered moon. Ganymede too has a subsurface ocean, which could potentially also host life. Just how deep this ocean is, and whether it exists in pockets or as a continuous band around the moon, are questions the Juice team hopes to answer.
Ganymede is also more complex. It is the only moon in the solar system with its own magnetic field, probably generated by a liquid-iron core like Earth’s. This field is even powerful enough to generate an aurora, like Earth’s. Understanding the origin of this field and how it interacts with Jupiter’s field is one of the key goals of the mission.
If all that isn’t convincing enough, Ganymede also has a tenuous oxygen atmosphere formed by the breakdown of water ice on the surface.
"Ganymede appeals to geologists, astrobiologists, magnetophysicists and atmospheric scientists," says Bunce. "It’s clearly a very rich environment, which is why we’re so excited to be going.”
The plan is to launch Juice in 2022 and for it to enter Ganymede orbit in 2032.