breaking the boundaries of science
Jupiter is the largest planet in our solar system and the planet with the most moons. To date, their number is estimated at between 82 and 95, with most having been discovered in the last two decades. JUICE is the first mission to receive funding of more than one billion euros as part of ESA’s Cosmic Vision programme. It seeks to find answers to four main questions – How did planets form and how did life appear? How does the Solar System work? What are the fundamental laws of physics in the universe? How did the present universe come into existence and what is it made of? JUICE was chosen ahead of other proposed missions because it was designed to address the first and last of these questions. The Hubble Space Telescope and NASA’s Voyager, Galileo, Juno spacecraft have already obtained some clues about this.
More water than Earth on ‘ocean moons’
NASA’s Galileo was the first to discover water on the Moon in 1995. Data collected by the space probe revealed vast liquid oceans beneath the crusts of not only its three icy moons, Callisto, Europa and Ganymede, but also on its volcanic moon, Io. In 2014, the Hubble Space Telescope discovered geysers on Europa. Their bases appear to be filled with salts, including carbonates. It is therefore likely that Europa may meet four of the criteria for life—the famous quartet of carbon, hydrogen, oxygen, nitrogen (CHN), symbolizing the main chemical elements that make up living beings, with liquid water acting as a solvent. serves as a form, energy and a stable environment (orbits, rotation, average temperature…) to enable the development of life. The Galilean moons further enjoy Jupiter’s gravitational energy, generating significant tidal effects and helping to satisfy the last two conditions above.
Why Ganymede is the main objective
Ganymede is set to be studied in more depth by Zeus than Callisto and Europa. This is not only because it is the largest moon in the Solar System, but also an oceanic moon with its own magnetic field. Similarly to Earth’s magnetosphere, Ganymede has the potential to protect life by diverting the flow of cosmic rays and radiation particles from Jupiter’s radiation belts. Along the way, Zeus must contend with the highest radiation levels in the Solar System. This means that its electronic modules must be housed in lead-shielded cavities and that the components must be “hardened” to help them resist the harsh environment. Zeus will also encounter extreme temperatures, ranging from +250°C to -230°C, as it flies past Venus in the Jovian system. To maintain a constant internal temperature, the spacecraft is coated with a multilayer thermal insulation made of gray silicon aluminum alloy, earning the probe the nickname “Silver Beauty”.
an energy problem
Around Jupiter, which is five times farther from the Sun than Earth, the satellite would receive 25 times less solar energy than around Earth. The spacecraft does not have radioactive batteries because Europe is not yet capable of producing them industrially, unlike the US, Russia and China. To enable tools and equipment to operate with 1000W (the power of a small hairdryer) it will rely on huge solar panels – their total surface area is 85m2 – which have been tested to withstand radiation and temperature variations. Has been done Built by 80 European companies under the direction of EADS Toulouse, the Zeus probe will have a wingspan of 28 m (the length of a basketball court), carrying a 2.5 m long communications antenna (necessary due to Jupiter’s distance from Earth). It weighs about 6 tonnes at liftoff (most of which is the propellant that will be spent propelling the probe) and carries ten instruments (in total, less than 280 kg).
Numerous pearls filled with billions of tons of water are scattered on the moon, ‘priceless treasure’ can quench the thirst of humans
ten scientific instruments on board
Of these instruments, France – with the assistance of Italy – primarily built the Moon and Jupiter Imaging Spectrometer (MAJIS). It is an instrument that will help the spacecraft determine the physico-chemical compositions of the lunar surfaces as it flies over them and thus detect CHONs associated with potential life. MAJIS will also study their ice sheets and liquid water. This will enable us to identify landing sites for future in situ exploration and to evaluate the composition and dynamics of Jupiter’s atmosphere. The spatial resolution of MAJIS is between 100 meters and several kilometres, depending on the probe’s altitude at the time, with an accuracy 10,000 times higher than the equivalent instrument on Galileo.
Finally, it should be noted that JUICE’s plans may be revised based on the latest results from NASA’s Juno mission. Juno is still orbiting Jupiter and has been flying over its poles since 2016. Juno’s nominal mission has been extended to flyby each of Jupiter’s Galilean moons, starting with Ganymede in June 2021 and ending with Europa in early 2023. These observations and subsequent data analysis will help Jupiter scientists reach better conclusions 12 years after Juno and 30 years after Galileo.
(Carol Lariguderie, Center National d’Etudes Spatiales (CNES))