Space probe JUICE
Launch to Jupiter's icy moons
Picture: ESA/ATG medialab (Sonde), NASA/ JPL/DLR
The European Space Agency ESA is sending the largest mission of the decade on its way. The JUICE space probe will search for indications of life on Jupiter's icy moons. That is conceivable, but it is not yet known whether the conditions are actually suitable for the existence of life.
Jupiter is a long way away. On average, Earth and the gas planet are separated by about 780 million kilometers. The 5.2-ton space probe Jupiter Icy Moons Explorer, or JUICE for short, will not reach its destination until July 2031. After leaving our planet, it will return in August of next year to gain momentum and increase its cruising speed to save fuel. This is known as a swing by maneuver and is tried and tested in space travel. JUICE will perform another such maneuver around Venus in August 2025. It will then perform two more such maneuvers on Earth in 2026 and 2029 before finally setting off in the direction of Jupiter.
Planetary system in miniature
Awaiting the probe is a wondrous world, almost a planetary system in miniature. At least 92 moons orbit the giant ball of gas we call Jupiter. There is Ganymede, the largest of all moons in our solar system. Its size even exceeds that of the planet Mercury. Its ice cover, probably several hundred kilometers thick, could hide an ocean that contains more water than all of the seas on Earth. At least, that's what the data sent to Earth by the Galileo spacecraft in the mid-1990s suggest. Callisto is a little smaller than Ganymede and completely littered with craters. Here, too, an ocean could be hiding in the depths. The surface of the moon Europa, on the other hand, is one of the brightest a moon has to offer and likely consists mainly of ice. Beneath the icy surface an ocean of 80 – 170 km depth is believed to exist.
Where liquid water is present alongside certain basic chemical building blocks and stable environmental conditions, astrobiologists see the possibility, in principle, for the emergence of life. It would be a sensational discovery that would change our view of the world if we were to find that life had arisen twice independently in our solar system.
Juice’s odyssey of exploration
Looking under the ice of the moons
"One of the biggest questions facing science today is the origin of life," says Christian Gritzner, head of the Solar System Missions Group of the German Space Agency at the German Aerospace Center (DLR). "We want to get closer to an answer to this with the JUICE mission." Radar instruments, for example, will find out whether the moons are suitable as habitats, penetrate the ice cover and provide detailed information on the oceans; spectrometers will analyze the composition of the ice, and a submillimeter wave instrument will record the temperature structure of the moons. The German Space Agency is playing an important role in this. As an international cooperation partner, it coordinates the various contributions of German research institutions and provides funding. "German research institutions such as the DLR Institute of Planetary Research, the Max Planck Institute for Solar System Research and many universities are involved in seven of the ten measuring instruments," Christian Gritzner is pleased to report. "Two of them are even being lead-developed and built in Germany." If everything goes according to plan, the probe's measuring systems will take a closer look at the gas giant and three of its largest moons starting in 2031. Jupiter's atmosphere and magnetic field will also be of interest. The scientists want to find out what influence these have on the moons.
Christian Gritzner. Picture: DLR
The researchers are also taking a closer look at Jupiter's moon Europa. They want to know how thick its ice cover is, and they are also on the lookout for landing sites in preparation for future missions. For example, the Europa Clipper mission planned by the U.S. space agency NASA. By 2034, JUICE is expected to fly past icy moons a total of 35 times at fairly close range. "You can find out a lot about the Jupiter system from Earth, but you can do much better research right on the spot. The Galileo and Juno missions then opened a door and provided an unimagined treasure trove of data," Christian Gritzner tells us. "With JUICE, we now want to expand these fragmented snapshots and assemble them into a much more detailed picture of Jupiter and its moons."
A temporary companion for Ganymede
Of very special interest, however, is Ganymede. And this in several respects. So far, no other moon is known to have its own magnetic field. JUICE will investigate this more closely. In addition, the researchers want to know how the interior of the moon is structured. What is the ice crust like? What layers can be found underneath? How deep is the ocean? JUICE will measure the entire surface of the moon several times point by point. This will not only produce a high-resolution three-dimensional map. The researchers also want to get to the bottom of the deformation of the satellite. "Ganymede is being tugged on by Jupiter's tidal forces. Jupiter's gravitational pull and the additional outward centrifugal force are pulling the moon elongated. And at the same time, the moon rotates around its own axis," explains Christian Gritzner "This really kneads Ganymede. This warms its interior and, according to calculations, could keep the ocean liquid."
At the end of 2035, it will then be time to say goodbye. And with a bang. Because JUICE won't just fall silent somewhere in the outer solar system, but will find its final resting place on Ganymede, through a planned crash.
The five most important questions about the JUICE mission are:
- What do Jupiter's ocean worlds look like?
- Why is Ganymede so unique?
- Could life exist - or ever have existed - in Jupiter's system?
- How did Jupiter's complex environment shape its moons and vice versa?
- What does a typical gas giant planet look like, how did it form, and how does it function?
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