Europe’s JUICE mission about to launch to explore Jupiter, here’s what you need to know

Europe’s mission to explore some of the solar system’s most mysterious ice worlds is scheduled to get underway on Thursday local time when the Jupiter Icy Moons Explorer (JUICE) is launched into space.

The mission – which will conclude a decade from now – is to chart Jupiter and three of its four largest moons – all of which are covered in thick ice sheets.

Below these frigid surfaces however, scientists expect to find potentially world-covering oceans.

As well as seeking to understand the interactions between our biggest planetary neighbours and its massive moons, the European Space Agency’s exploration of the Jovian system hopes to extend knowledge of planet formation and how it may support the emergence of life.

Even so, it’s unlikely that JUICE is about to find even simple lifeforms beneath the ice, though Ganymede – the principal target of the mission – does possess a magnetic field similar to Earth’s.

JUICE: Why we won’t know much for nearly a decade

“JUICE, the spacecraft, has taken the better part of the past decade to be designed and developed and is now ready,” Alessandro Atzei, JUICE’s payload system engineer said ahead of Thursday’s launch.

“We’re talking about a rather large spacecraft with many key features that really are striking… once deployed the huge solar arrays are 85 square metres.

“It will take quite some time to arrive at Jupiter… in the distant July of ’31 and then the real mission will start. We’ll [first] focus on Europa, then we’ll go to a high latitude phase which is basically focussing on the polar areas of Jupiter itself.”

About 30 minutes after launch on Thursday, JUICE will separate from Ariane 5 and ground stations on Earth will begin tracking the spacecraft. Then the slow process of unfurling the space craft’s infrastructure will begin. Over the course of 17 days, all of JUICE’s solar arrays, probes, antennas and booms will be deployed so the craft can begin its journey out of Earth’s neighbourhood.

In total, the JUICE spacecraft is about the size of two tennis courts and, including fuel, weighs about as much as an adult elephant.

Juice is prepared for loading onto the ariane 5 spacecraft.
JUICE is prepared for loading onto the Ariane 5 spacecraft. Credit: ESA-CNES-ArianeSpace/ Optique vidéo du CSG, S Martin

What’s JUICE going to do?

Jupiter is a unique planet in our solar system and entirely different to Earth. It’s a gas giant with a magnetic field 20 times more powerful than Earth’s. The JUICE mission will try to understand how Jupiter’s unique properties have influenced the formation of its largest moons as well as the wider planetary system which consists of more than 90 moons. This includes understanding the characteristics of the ice-covered Ganymede, Callisto and Europa

Jupiter, as seen in 2017 from NASA’s Hubble Space Telescope / Credit: NASA, ESA, and A. Simon (NASA Goddard)

What are the mission targets?

Jupiter is the biggest planet in the solar system – a 142,000-kilometre-wide world that would fit more than 1,300 Earths inside it.

Its massive atmosphere is about nine tenths hydrogen, and the rest mostly helium, with tiny traces of methane and other gases. It also pulls 92 moons into its orbit, among which are the Galilean moons – the first non-planets outside of our own Moon to be observed by the astronomer Galileo Galilei in 1610. Three of these moons are covered in thick icy shells and are the targets of interest for the JUICE mission.


Depiction of jupiter's moon ganymede, a brown, cratered sphere against a black background.
Depiction of Ganymede centered over 45° W. longitude. Credit: National Oceanic and Atmospheric Administration

The largest moon in our solar system, (and around half the size of Earth), Ganymede is believed to possess a saline ocean under its ice-covered surface. Scientists believe this ocean may cover the entire world. It also generates its own magnetic field, a characteristic shared only by the Earth and Mercury in our solar system. It also possesses a unique, billions of years old geological history as one of the oldest space bodies in our solar system.


Callisto as seen by nasa's galileo spacecraft.
Callisto as seen by NASA’s Galileo spacecraft. Source: NASA/JPL/DLR

The second largest moon orbiting Jupiter, Callisto is a fraction smaller than Mercury and bigger than the dwarf planet Pluto. Callisto is another ancient world that appears to have ceased geological activity for at least a billion years. This will give scientists an idea of what the space environment around Jupiter might have been like in the early formation of the planet and its children.


Jupiter’s icy moon Europa will be visited by NASA’s Europa Clipper probe, launching in 2024. Credit: NASA/JPL-Caltech/SETI Institute

Europa’s veiny surface is mainly ice, and likely conceals a liquid ocean beneath. For this reason it has been suggested as a possible home for simple life (and was featured in classic science fiction works like Arthur C. Clarke’s Space Odyssey series for this reason). It’s also hypothesised that plumes of ocean and ice may erupt from the surface into space.

What about Io?

The third-largest of the Galilean moons, Io is the most volcanically active place in the solar system with kilometre-high lava plumes thanks to gravitational interactions with Jupiter and its neighbouring moons Europa and Ganymede. Unsurprisingly, Io’s volcanic nature keeps it ice-free and so won’t be explored in detail as part of the JUICE mission (it’s also unlikely to have life for this reason).

The moon io
Io, as seen from Voyager. Credit: NASA/JPL/University of Arizona

How is JUICE getting to Jupiter?

On April 12 (local time), the JUICE spacecraft will be blasted into space on board an Ariane 5 rocket from the European Space Agency’s spaceport in Kourou, French Guiana. After launch it will perform a series of flybys of Earth, the Moon and Venus to calibrate its course towards Jupiter. This series of flybys is imperative to the mission – effectively juicing (pardon the pun) the spacecraft with gravity assistance to increase its momentum and slingshot it towards its target planet. These flybys will take place in August 2024 (Earth and Moon), August 2025 (Venus), September 2026 (Earth) and January 2029 (Earth) – that means JUICE will spend six years simply building up its speed to arrive at its destination.

In July 2031, it will start a three-and-a-half-year tour of Jupiter and its icy moons, before a final tour of Ganymede in December 2034 and then smashing into its surface in September 2035.

Summary of juice's instrumentation payload.
Summary of JUICE’s instrumentation payload. Credit: ESA

What’s on board JUICE?

To achieve its job, JUICE is carrying 10 specialised instruments. These include:


This optical camera is the spacecraft’s eye. It will image the moons’ surfaces at a resolution of 2.4 metres, and the clouds of Jupiter at 10km.

MAJIS: Moons and Jupiter Spectrometer

This instrument will cast a different eye on Jupiter’s clouds and moon surfaces. A spectrometer can be used to determine the composition of these phenomena, such as what chemicals constitute the planet’s atmosphere and the ice sheets of Ganymede, Callisto and Europa.


The UVS is JUICE’s ultraviolet imaging spectrograph, which will study Jupiter’s aurorae and the composition of the planet and moons’ uppermost atmospheres.

SWI: Sub-millimetre wave instrument

SWI is a radio telescope that will measure infrared radiation in Jupiter’s stratosphere and troposphere, as well as the moons’ exospheres and surface.

RIME: Radar for Icy Moons Exploration

This instrument will emit radio waves capable of penetrating the thick ice of Ganymede, Callisto and Europa to depths of up to 10 kilometres. This will allow the JUICE mission to map the nature of the moons’ surfaces and peer below the ice to understand what lies beneath.

GALA: Ganymede Laser Altimeter

Altimeters measure altitudes of objects – like an orbiting spacecraft – above a surface. GALA will seek to understand the topography and tectonics of the moons by emitting laser pulses to ping the surface of the world below.

3GM: Gravity and Geophysics of Jupiter and Galilean Moons

This instrument combines a radio transponder, oscillator and accelerometer to study the gravitational and physical effects of the study worlds. It will study Ganymede’s gravitational field, orbit and tidal effects. It will also study the ionosphere of the four worlds.

J-MAG: JUICE magnetometer

This instrument uses sensors to determine how Jupiter’s extensive magnetic field interacts with Ganymede.

PEP: Particle Environment Package and RPWI: Radio and plasma wave instrument

These instruments use sensors to study charged particles within the Jupiter system.

Please login to favourite this article.