Jupiter's four Galilean moons. Credits by: NASA/JPL/DLR

JUICE, ESA’s most important mission, is ready to take off

JUICE, the ESA Mission whose main objective is to study three icy moons of Jupiter, it's about to reach Kourou, from where it will be launched in April

JUICE is about to leave Toulouse for Kourou, where it will be launched on an Ariane 5 rocket in April 2023. As announced by Airbus, the spacecraft is expected to leave France in a few days.

Ariane 5 flight VA-256 on the launch pad with the James Webb Space Telescope. Credits by: NASA’s James Webb Space Telescope
Ariane 5 flight VA-256 on the launch pad with the James Webb Space Telescope. Credits: NASA

What is “JUICE”?

Selected as part of the Cosmic Vision 2015-2025 planetary exploration program, the Jupiter Icy Moon Explorer (JUICE) is a European Space Agency mission whose main objective is to study three icy moons of the gas giant Jupiter. The exclusion of Io from the list of moons to be explored is that the other three moons contain a significant amount of liquid water beneath the thick blanket of ice that forms the surface of the moons.

The JUICE probe, which took about a year to build in Germany, successfully passed all its tests and in August 2021 the spacecraft was sent to Airbus in Toulouse for final assembly and various tests. More than 500 people worked at Airbus, assembling some of the spacecraft’s instruments and installing the most advanced solar panel system ever used on a planetary exploration mission.

Artist's impression of the Jupiter Icy Moons Explorer, JUICE. Credits by: ESA/ATG medialab
Artist’s impression of the Jupiter Icy Moons Explorer, JUICE. Credits: ESA/ATG medialab

Once on its way, the spacecraft will arrive at Jupiter around 2030 and begin a three-year study of the Jovian system and its Galilean moons.


Mission objectives

There are a lot of important accomplishments to be reached, for example to study Jupiter’s atmosphere and magnetosphere. Other ones are:

  • To analyze Europa’s ice cap, find a suitable site for future robotic exploration, and learn about the ocean of liquid water that lies beneath the surface ice of the moon itself.
  • To study the icy surface and internal structure of Ganymede, gathering data on the possible liquid water ocean beneath the icy surface and its magnetic field. Note that Ganymede is the only moon in the Solar System with a magnetic field.
  • To study the icy surface of Callisto, the most cratered moon in the Solar System.
JUICE in the Jovian system. Credits by: ESA/M. Carroll
Illustration of JUICE probe in the Jovian system. Credits: ESA/M.Carroll

The Jovian environment and its moons

Jupiter is the fifth planet in the Solar System in distance from the Sun, but the first in size and mass. Because of its composition, Jupiter is called a ”gas planet” because it consists almost entirely of gases, such as molecular hydrogen, helium, methane, ammonia, ethane, and oxygen.

Jupiter is often referred to as a “missing star”, but this is not quite correct as to “shine” Jupiter would have to be more than 80 times more massive.

Due to the Kelvin-Helmholtz mechanism, the planet compresses by 2 cm per year. This compression causes the core to heat up more and more, and the endogenous heat emitted into space increases more and more. This is why the Jovian environment is much more radioactive than any other planetary environment in the Solar System.

The image of Jupiter captured by the Hubble Space Telescope Credits by: NASA/ESA/J. Nichols (University of Leicester)
Image of Jupiter captured by the Hubble Space Telescope. Credits: NASA/ESA/J. Nichols (University of Leicester)

Jovian system is often considered a small planetary system because of the large number of natural satellites orbiting it: 80. The most important of these are the first four, known as the “Medici” because Galileo Galilei first discovered them in 1610.

Jupiter's four Galilean moons. Credits by: NASA/JPL/DLR
Jupiter’s four Galilean moons. Credits: NASA/JPL/DLR

The first satellite to be studied by the JUICE probe is Europa, a moon characterized by a thick surface ice sheet and a deep subsurface ocean of liquid water. Interaction with Jupiter should heat the ocean to a point where it could potentially support primitive life forms.

Ganymede is the third Medicean satellite of Jupiter and is the largest moon in the Solar System, larger even than the planet Mercury. Ganymede consists mainly of silicates and water ice and has a core of molten iron. 200 kilometers beneath its icy surface, Ganymede may contain an ocean of liquid salt water. The darker areas on its surface are thought to be the result of tectonic activity due to tidal heating by Jupiter.

Finally, there is Callisto, another icy moon that could host a shallow ocean of liquid water. Because of the many craters that characterize its surface, it has been studied that the moon has no plate tectonic activity, nor geysers that could cover the craters with ice. Because of its distance from Jupiter, Callisto has been described as an ideal location for a possible human settlement in the outer Solar System.


On-board instruments and the Italian contribution

JUICE is a 6.2-tonne spacecraft that will be equipped with a high-resolution camera, three spectrometers, a magnetometer, a radio wave instrument, and a laser altimeter. JUICE also has a 3-meter diameter antenna that will be used to send 1.4Gb of data to Earth every day, and two tanks, the first full of nitrous oxide and the second containing propellant.

The JUICE mission will see a major contribution from Italy, in particular from ASI (Italian Space Agency), which has been working with ESA since 2004, on an ambitious plan for space exploration to be implemented in the near future and on cutting-edge instruments to be installed on robotic probes.

JUICE on-board instrumentation. Credits by: ESA
JUICE’s on-board instrumentation. Credits: ESA

JUICE will be equipped with entirely Italian solar panels and the system promises to be the largest photovoltaic generator ever designed for a space mission. Once opened, the panels will cover an area of no less than 97 square meters, which will ensure the right power supply for a probe that will be 800 million kilometers away from Earth, at an average temperature of -220 degrees Celsius. The trick is to use gallium arsenide, which can convert sunlight into electricity even at extremely low temperatures and in low light.

To pay tribute to Galileo, who was the first to observe Jupiter in detail and discovered four of its moons in 1610, the JUICE spacecraft will carry a commemorative plaque with a reproduction of the ‘’Sidereus Nuncius’’.

The missed Russian lander

The JUICE mission originally envisaged working with the Russian Space Research Institute to build Laplace-P, a lander to be dropped on Ganymede that would carry an astrobiology laboratory. Unfortunately, this project was not very successful and was canceled.


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Marco Fiaschi

Marco Fiaschi

I'm Marco, 25 years old from Gaeta, with a passion for astronomy, music and computing. I study Computer and Telecommunications Engineering and i'm the founder of 'Verso l'infinito...e oltre!'

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