The European Space Agency’s first dedicated mission to the icy moons of Jupiter has launched successfully.

JUICE launch
Liftoff! Ariane 5 launches with JUICE.

An exciting new planetary mission took to space today, headed to the largest planet in the solar system. The European Space Agency’s Jupiter Icy Moons Explorer (JUICE) lifted off from pad ELA-3 at the Guiana Space Centre in French Guiana atop an Ariane-5 rocket. Liftoff occurred on Friday, April 14th, at 8:14 a.m. EDT (12:14 Universal Time, or UT).

The launch was nominal. JUICE successfully separated from the Ariane upper stage at T+28 minutes after launch, ESA's New Norica ground station in Australia acquired signals from JUICE at T+38 minutes, and the spacecraft deployed its solar panels and is in good health a bit early at T+1 hour, 18 minutes after launch. The launch was delayed one day from April 13th, due to weather concerns at the launch site.

This was also one of the heaviest interplanetary launches to date: The JUICE mission had a launch mass of 5,963 kilograms, versus NASA Cassini at 5,712 kilograms. The heaviest remains the Soviet Union's Phobos 1 and 2 missions, which both tipped the scales at 6,220 kilograms.

JUICE team group photo
The JUICE mission control team.

Now, JUICE will take the long road to Jupiter, making one flyby past Venus in August 2025 and three past Earth in August 2024, September 2026, and January 2029, before arriving at Jupiter in July 2031. JUICE also has the option to fly past the asteroid 223 Rosa in October 2029.

JUICE is also ESA’s first flagship mission to the outer planets. JUICE will be joined later next year when NASA launches Europa Clipper in October 2024. Europa Clipper will be the first planetary mission launched on a Falcon Heavy (excluding the Tesla Roadster). Although Europa Clipper launches later, it will reach Jupiter a bit earlier, on April 11, 2030.

JUICE will explore the large icy moons Europa, Ganymede, and Callisto, in an effort to address key questions on habitability and whether these icy worlds harbor internal oceans. The mission was first conceived in 2012 as a top priority for ESA’s Cosmic Visions program, and international partners on the project include NASA and the space agencies of the UK, France, Italy, and Japan.

Galilean moons composite with the Great Red Spot showing on Jupiter
A montage of Jupiter's moons (from top to bottom) Io, Europa, Ganymede, and Callisto.

“JUICE will address two top-level questions: What are the conditions for planet formation and emergence of life, and how does the solar system work?” says project scientist Oliver Witasse (ESA). “Its mission themes are to examine the emergence of habitable worlds around gas giants, with the Jupiter system as a model for gas giants in the quest to better understand exoplanet systems.”

JUICE follows Juno’s precedent as a solar-powered mission. Early flyby missions such as the Pioneer and Voyager missions all utilized nuclear-fueled MMRTGs (Multi-Mission Radioisotope Thermal Generators). Solar power is difficult to use out by Jupiter, as the mission must utilize sunlight that’s just 3% the strength of that received on Earth. Thankfully, solar-panel development has come a long way in recent years. Europa Clipper will use the same newer, gallium-arsenide panels as JUICE and reach 30% efficiency, versus 20% for ESA’s comet-shepherding Rosetta mission.

JUICE solar panels
Testing JUICE's solar panel deployment on Earth.

The 10 instruments aboard JUICE include high-resolution cameras, an imaging spectrometer and UV imaging spectrograph, an ice-penetrating radar, and a laser altimeter.

One innovative instrument aboard JUICE is J-MAG (the JUICE Magnetometer) which will probe interior oceans. J-MAG was built by Imperial College London, which also supplied the magnetometer for Cassini, an instrument that helped discover a possible global ocean under the ice of Saturn’s moon Enceladus.

“The JMAG instrument would be instrumental in comprehending the ocean worlds,” says Shivangi Sharan (Imperial College London). “Ganymede, Callisto, and Europa seem to have an ocean beneath their surface. JMAG would be able to provide the characteristics of these oceans. The focus is on Ganymede, which is the only moon in the solar system to have its own magnetic field and magnetosphere. This magnetic environment is embedded in the larger magnetosphere of Jupiter. Their interaction is an important aspect that JUICE hopes to decipher.”

The instruments, including the magnetometer, will switch on periodically every six months to test performance and record the local solar environment.

JUICE in the cleanroom
JUICE prepped for launch.

JUICE will complete 35 flybys of Jupiter's primary moons during its nominal mission. Ultimately, JUICE will settle into an orbit around Ganymede — the largest moon in the solar system — in December 2034. JUICE will end its mission will an impact on Ganymede in late 2035, though an extended mission could prove useful.

“JUICE will be in orbit around Ganymede at the end of its mission, the first spacecraft to orbit the moon of another planet,” says Randy Gladstone (Southwest Research Institute). “If there’s enough fuel left, it may be possible to lower the 500-kilometer circular orbit to 200 kilometers, allowing surface maps of higher spatial resolution.”

Observers in Australia, New Zealand, and southeast Asia can also track JUICE as a 13th-magnitude object tonight on its outbound flight from Earth. NASA’s JPL Horizons will list ephemeris for the JUICE mission — astronomer Gianluca Masi and the Virtual Telescope Project will also host a live tracking session online tonight, starting at 19:00 UT/3:00 p.m. EDT.

It will be exciting to see JUICE and Europa Clipper explore Jove in the coming next decade, as humanity unlocks the secrets of the ice moons of Jupiter.


Image of Yaron Sheffer

Yaron Sheffer

April 14, 2023 at 3:27 pm

A bit of nitpicking is in order. This is not ESA's first mission to the outer planets, if you recall Huygens, the ESA probe that landed on Titan. True, it got a ride from the Cassini mission, but the end result was a very successful ESA landing on another moon, the only such achievement so far.
And now for the long wait... 8 years! Spaceflight is so much faster in the movies 🙁

You must be logged in to post a comment.

Image of Ludovicus


April 14, 2023 at 4:44 pm

I guess the reason for this sauntering trek to Jove is the mass of the craft - pretty large! Still, would be nice ot see it there in 4-5 years instead of nearly double this!

I hope that the team avails themselves of the Venus flyby and maybe even an Earth one too - to perhaps get even more data about our outer magnetosphere during the flyby. Could yield useful home-bound data! Plus they can check the solar panels for battery testing.

I still do not understand the need to splay out acres of solar panels - makes way more sense to use MMNTGs - even a small one, as a standby backup if needed. Well - here's hoping nothing hits a critical panel en route! 🙂

Bon voyage, Juice! Please be "sweet" in the years to come! lol


You must be logged in to post a comment.

Image of David Dickinson

David Dickinson

April 14, 2023 at 6:40 pm

Yup. My bad, I 'spaced' out and forgot Huygens. Good catch, corrected.

You must be logged in to post a comment.

You must be logged in to post a comment.