Jupiter is seen in the back with a glowing storm on its north pole. The Juice spacecraft is toward the top left and a few moons are scattered throughout the image, one is very close at the bottom, partially off-screen.

An artist’s concept of ESA’s Juice mission in Jupiter’s “solar system” of moons.

Jupiter is something of a spectacle. It’s home to a tangerine storm larger than Earth, keeper of peachy winds so frigid they’d likely freeze your body on impact, and owner of 83 moons — having recently stolen Saturn’s crown for the planet with the most lunar friends. Even its enormity is barely comprehensible. Take every planet in our solar system, slap their masses together, multiply that by two and you get a chunk about the size of it. 

Who knows what could be going on over there. I mean, really. 

Which is why the European Space Agency has a grand plan. ESA is getting set to send a next-gen space probe to join NASA’s Juno orbiter in studying the Jovian lifestyle. It’s called Juice, or the Jupiter Icy Moons Explorer. And currently, Juice is being given its final touches in preparation for an exciting April launch date. 

Basically, this spacecraft “will make detailed observations of the giant gas planet and its three large ocean-bearing moons — Ganymede, Callisto and Europa — with a suite of remote sensing, geophysical and in situ instruments,” ESA said in the mission’s overview. Last year, the agency also laid out five mysteries it wants to tackle once Juice gets to its destination in, hopefully, 2031. 

We’ll discuss those mysteries in a moment, but here’s some quick information about Juice’s potential launch day so you can update your calendars. 

The spacecraft, which looks like a robotic box attached to two wings made of five solar panels each, is expected to launch in the middle of the month. It’s poised to head to space atop an Ariane 5 rocket, the same model that propelled the trailblazing James Webb Space Telescope to its station, about a million miles from Earth, two Christmases ago. 

After a bunch of mid-space maneuvers and gravity assists, Juice would reach Jupiter by the year 2031 — and in 2034, if all goes well, Juice will orbit the moon Ganymede. That’d make it the first spacecraft to traverse the gravitational tides of a moon other than our own lunar companion.

“Large in the night sky, Jupiter was naturally a target for one of the first telescope-assisted stargazers, Galileo,” ESA said. “His observations, from 1610, discovered Io, Europa, Callista and Ganymede, and showed them to move, relative to Jupiter, from night to night — suggesting the controversial notion that Earth was not the sole center of motion in the universe.”

As such, the agency says Juice will carry a plaque in honor of Galileo to the brilliant scientist’s beloved, planetary muse.

What will Juice look for?

ESA’s first major question is the obvious one you might have guessed from Juice’s full name and that I’ve touched on already: What’s going on with Ganymede, Callisto and Europa? 

In short, these three moons are at the forefront of the agency’s endeavor because they’re all suspected to have some sort of water on, or under, their surfaces. “Scientists believe that Callisto, Europa and Ganymede hold vast quantities of water buried under their surfaces in volumes far greater than in Earth’s oceans,” ESA said in a statement.

Europa, in particular, is projected by astrobiologists to have a hefty amount of H2O — and of course, water equals the potential for alien life, which leads us to another of Juice’s queries.

Has there ever been life on any of Jupiter’s moons — or, I guess, on Jupiter? 


Jupiter, center, and its moon Europa, left, are seen through the James Webb Space Telescope’s NIRCam instrument 2.12 micron filter. 

NASA, ESA, CSA, and B. Holler and J. Stansberry (STScI)

In truth, probably not on the latter. That’s simply because there’s neither land nor water on this planet. There’s only gas and atmospheric water vapor. If you tried to stand on Jupiter, you’d just fall in until you were crushed by the planet’s immense gravity concentrated toward the center. And… that’s if you could make it that far in the first place.

But with regard to Europa, an icy world very much with solid ground, scientists currently have this region at the top of their lists of places we might find evidence of extraterrestrial life. In fact, NASA is also building a spacecraft dedicated to scanning Europa for such remnants. It’s called the Clipper, and it’s quite impressive.

Next, turning to Ganymede, another of ESA’s wonders is: Why is Ganymede the only moon in our solar system with its own magnetic field? 

This one’s pretty odd. Ganymede’s magnetic field is so strong that it even gives rise to auroras in its atmosphere, similar to the way Earth’s magnetic field produces the northern lights when electrons get caught within.

But for some unknown reason, the rest of our solar system’s moon community can’t relate to Ganymede’s magnetic ventures. It’s an outsider that way. “Juice’s tour of Jupiter will include multiple flybys of these ocean-bearing moons, before culminating in orbit insertion around Ganymede — the first time a spacecraft will have orbited a moon in the outer solar system,” ESA said. 


A visualization of Ganymede in the shadow of Jupiter, with its aurorae glowing.


Further, getting a little more general, ESA also wants to know if, and how, Jupiter’s complex space environment shaped the trajectory or conditions of its moons. With 83 individual satellites orbiting it, this Jovian world basically holds its own solar system if you think of Jupiter as the “sun.”

And finally, the fifth and final box ESA hopes to tick while dissecting Jupiter is how such colossal balls of gas come into existence in the first place. Though colored with hues on the cooler end of the spectrum, Uranus, Neptune and Saturn are also wispy cradles of zippy molecules floating around our solar system. What would give rise to these extreme mini-universes?

Hopefully, we’ll soon have some answers. But it all begins with that April launch. We’ll keep you updated as the days go by.

Leave a Reply

Your email address will not be published. Required fields are marked *