Frequently Asked Questions
Who built Juice and how long did it take?
Juice was built by an industrial consortium led by Airbus Defence and Space (Toulouse, France), based on requirements set by ESA. The development phase started in mid-2015. The production of the flight model started in 2019 and was completed in mid-2022.
How is Juice powered?
Juice’s power comes mainly from its large solar array. It was proven that a mission at Jupiter can be designed with solar panels, and therefore a radioisotope thermoelectric generator (RTG) – such as that used by the NASA/ESA/ASI Cassini-Huygens mission – was deemed unnecessary. The solar panels will generate around 700–900 Watts. The spacecraft is also equipped with batteries that allow it to survive periods of up to around five hours in the shadow of Jupiter.
Is Juice able to detect life?
Juice is not equipped to detect life. The mission is designed to find out whether there could be places around Jupiter, inside the icy moons, where the necessary conditions (water, biological essential elements, energy, and stability) to sustain life are present.
What kind of life could be present in the oceans of Europa, Ganymede and Callisto?
If life is present on these moons, it is most likely in the form of microbes. More advanced species might also be present, like the ones we detect in deep-sea trenches and at hydrothermal vents on Earth, such as various kinds of coral, worm, mussel, shrimp and fish. They might, however, be so different from the life forms we are familiar with that we have no current means to classify them. Possibly even so different that we cannot even detect them.
Will the spacecraft be sterilised? Could Juice bring life to Jupiter?
No, Juice will not be sterilised. The mission will therefore bring a miniscule number of cells (spores) from Earth with it. Icy moon Europa is the only object that is considered to have the potential for harbouring life, and that therefore needs to be protected. Juice has been designed to reliably maintain control of itself, so the likelihood of accidentally colliding with Europa and potentially contaminating it with cells from Earth is below the requirement for planetary protection.
If we discover, before entering into orbit around Ganymede, that this moon is habitable, we will follow the requirements for planetary protection. But as it stands, planetary protection rules allow a crash onto Ganymede, because there are no indications that the deep subsurface ocean on Ganymede can be in contact with the icy surface. Crashing into Europa would not be allowed because Europa's subsurface oceans are suspected to be less deep and therefore contamination from the surface to the ocean would in theory be possible.
How can an orbiter like Juice be used to detect liquid water underneath the crust of Ganymede and other icy moons?
Juice will not touch the liquid directly to make in-situ measurements, but there are a few methods to detect liquid water indirectly from orbit using instruments on board:
- With the magnetometer – The oceans of the icy moons are salty and therefore carry electricity. Plus, they are embedded inside Jupiter’s magnetic field, which varies over time. The combination of these two aspects (salty water, and Jupiter’s changing magnetic field) is responsible for the creation of a weak magnetic field around the icy moons which can be detected by a sensitive magnetometer.
- With the laser altimeter – Like the Earth experiences tides caused by our own Moon, Ganymede’s surface is deformed as it orbits around Jupiter. Precise measurements of surface displacements by Juice’s laser altimeter will indicate the presence of a subsurface ocean. If a subsurface ocean exists, the size of these displacements can be several metres, while without an ocean it is just a few tens of centimetres.
- With the radio science experiment – By measuring the gravity field of Ganymede and its variation over time with Juice’s radio science experiment (3GM), we will be able to detect an internal ocean and deduce some of its properties.
- With remote sensing instruments – Just like Earth, and also Jupiter, Ganymede has its own auroras. A very special method of detecting water is to measure slight shifts in Ganymede’s auroral ovals with Juice’s remote sensing instruments. The size of these shifts will tell us whether there is an internal liquid ocean.
Juice’s radar will explore the ice down to a depth of 10 km. The subsurface oceans are likely to be deeper, therefore not detectable by the radar. However, the radar will search for pockets of liquid water under the most active sites of Europa’s surface.
Why will Juice orbit Ganymede and not Europa?
There are two reasons. Firstly, Ganymede is a unique and fascinating object; it is the largest moon in the Solar System, the only moon with an internal magnetic field, it has a unique geological history and it harbours a large subsurface ocean. Secondly, the radiation environment is very harsh around Europa because it is much closer to Jupiter; this also explains why Juice will make only two flybys of Europa.
Will Juice work together with NASA’s Europa Clipper?
Whilst Europa Clipper is really focused on the moon Europa – including investigating whether the icy moon could have conditions suitable for life, Juice will study many targets (three icy moons, Jupiter's atmosphere, magnetosphere, Io, smaller moons, Jupiter's rings) with a special focus on Ganymede.
Having two missions in the Jupiter system at the same time is a great opportunity for science. The Europa Clipper science team and Juice science team are already working together to maximise the scientific harvest of the two missions. A joint meeting is organised approximately once per year and the two teams are in regular contact in between meetings. Recently, a steering group was formed that is dedicated to this collaboration, including members of both teams.
How will Juice complement NASA’s Juno mission?
Since arriving at Jupiter in July 2016, NASA’s Juno mission has been orbiting the gas giant every 53 days, capturing stunning high-resolution snapshots as it goes. Juice will complement Juno by taking a more global view, watching Jupiter as a whole system continuously to monitor how it is changing over time. This is vital for understanding Jupiter’s complex atmosphere, much of which we have never observed before.
What we see when we look at Jupiter – the distinct coloured bands, the intricate swirls, the Great Red Spot – is Jupiter’s lower atmosphere, the weather layer. This is the part that Juno focuses on. Juice, on the other hand, will tackle the upper atmosphere, using four instruments that each looks at a different wavelength of light to probe how temperatures, wind patterns and chemistry are changing in this part of the atmosphere.
What will Juice do between close encounters with Jupiter's moons?
Juice will observe Jupiter itself, take measurements in the planet's magnetosphere, and carry out remote observations of Jupiter's moons, including Io.
What will Juice tell us about Jupiter's shrinking Great Red Spot?
We can see from Earth that Jupiter's Great Red Spot is shrinking and starting to interact with other storms. To really understand this new phase of existence, Juice will look at how the storm changes over many years. Inside the Great Red Spot, gases are ‘cooked’ by ultraviolet rays from the Sun to form potentially unique molecules; Juice will use spectroscopy (looking at the wavelengths of light being absorbed and emitted by molecules inside the storm) to uncover the strange chemical processes taking place.
When will we get the first images and results from Juice?
The science mission will start around six months before arrival at Jupiter; images of Jupiter will be taken from a distance at that time and released soon afterwards. Juice’s first science flyby of a Jovian moon (Ganymede) and first passage close to Jupiter will occur in February 2032; image highlights will be released soon afterwards.
Concerning the first results, the science that Juice will undertake is very broad, covering Jupiter’s atmosphere, magnetosphere and rings, the Galilean moons, and more. It is difficult to predict when the first results will be available, but it will definitely be sometime in 2032.
Some images and data will be collected during the interplanetary transfer, for example during the flybys of Earth and Venus. We expect to be able to share some images and data following these milestones.
Can we follow where Juice is on its journey?
Is ESA already thinking about the next mission to ocean worlds?
The icy moons of the outer Solar System will be at the centre of ESA’s future exploration – it is the theme of the first Large mission of ESA's Voyage 2050 programme and has been designated as an ‘inspirator’ by the ESA Director General.