In December 2034, thunderous applause and cheers can be expected at the ESA control center in Darmstadt, Germany. The excitement will not be without reason either. The spacecraft JUICE has entered orbit around Ganymede, Jupiter’s largest moon, after an 11-year journey through the solar system.
The event will mark a turning point in the history of space travel. When the spacecraft soars into orbit, it will be the first time a spacecraft has orbited an alien moon.
This will also be the culmination of a major project that ESA has been very proud of since 2012.
Oceans beneath the ice may hold evidence that life can form elsewhere than on Earth.
JUICE (Jupiter Icy moons Explorer) is a kind of long-distance ESA flagship , and the goal is to study three of Jupiter’s large, ice-covered moons, much more closely than has been possible before.
With their variousmeasuring instruments, the scientists hope to gain a great deal of knowledge about the history of the moons, their structure and geology – and possibly also get answers to the big question: Could hidden oceans on these moons harbor life?
If it turns out to be the case, it will not only be the discovery of the century, but also proof that life can form on planets other than Earth, and that our existence is not a completely isolated coincidence.
All pre-tested
The price tag on the JUICE project says a lot about the size of the project by the standards of the European Space Agency. When the Ariane 5 rocket lifted off the spacecraft from the launch pad in French Guiana in April 2023, it can be said that ESA threw 1.5 billion euros into uncertainty.
But in fact, everything possible had been tried in advance. Tests have been carried out in ESA’s large space simulator, which is a vacuum space 10 meters wide and 15 meters high. There it is possible to simulate the situations that JUICE encounters on its way.
In the simulation, it was tested whether the unusually large solar panels of the spacecraft, which will be 85 square meters in total and the largest on any spacecraft, worked as expected.
During the space launch, the solar panels were folded in ten units, and it decided the fate of the entire mission that they managed to fold out perfectly.
The solar panels must both ensure that the fuel is sufficient for all phases of the mission and provide electrical current for all the scientific instruments of the spacecraft.
The spacecraft is supposed to withstand temperature fluctuations of 430 degrees.
At ESA, people breathed a sigh of relief when this 6.2-ton spacecraft was safely launched into space and the solar panels fell into place. However, the spacecraft still has many difficulties to overcome.
In the first part of the journey, the spacecraft has to swing quite a few times close to the Earth, the Moon and Venus before the direction is finally taken on Jupiter far out in the solar system.
Both the solar panels and the spacecraft itself have to withstand enormous temperature differences, ranging from 250 degrees at Venus to 180 degrees below zero at Jupiter. Added to that is the massive radiation from the gas giant.
Highlights of the trip
When the JUICE spacecraft lifted off from the launch pad in French Guiana in April 2023, a very eventful journey began, including a quick trip to Venus and then a look at the meteorite belt before arriving at the terminus around Jupiter.
April 2023: Reaches full size
An Ariane 5 rocket will launch the spacecraft in April 2023. JUICE has its long journey of deploying the solar panels, which total 85 square meters.
August 2025: Venus swing
First, JUICE passes the ground closely several times to save fuel. Gravity increases speed, and the same will happen when the spacecraft takes a swing around Venus in August 2025.
October 2029: Meteorites visited
Along the way, JUICE will pass through the meteor belt twice and will be able to view these small celestial bodies up close. One of them could be 223 Rosa, which is 80 km in diameter.
July 2031: Arrive at Jupiter
In July 2031, JUICE reaches all the way to Jupiter and its 80 moons. Over the next three years, the spacecraft will fly close by the large icy moons Ganymede, Europa and Callisto a total of 30 times.
December 2034: In orbit around the moon
JUICE will be the first spacecraft in history to orbit a distant moon in December 2034. The orbit around Ganymede will be circular and at an altitude of 500 km.
But if everything goes well, the trip to Jupiter and its moons will take more than 8 years. Jupiter’s moons are about 80 in total, but four of them are by far the largest: Io, Europa, Ganymede and Callisto. They are often called the Galilean moons after Galileo Galilei who discovered them with his telescope in 1610.
Water on 3 out of 4 moons
Of these moons, Io is the closest to Jupiter and is the planet in the solar system with the most terrestrial activity, but it is the other three moons that are now attracting more interest.
Namely, they bear all the signs that there is a huge amount of water in liquid form – and with that, life could possibly be hidden on these planets. Although the ice shell on the outside is about 100 km thick, there are probably enormous watery oceans under the ice, and astronomers believe that the total amount of water can be ten times the amount of water on Earth.
Measurements made by the Galileo spacecraft in the last decade of the last century showed that Jupiter’s magnetic field lines curve around Europa in such a way that it suggests that the planet is hiding an electrically conductive liquid. The easiest way is to think that the liquid is salt water that conducts an electric current.
Through the Hubble telescope, astronomers have since seen water eruptions that reach 160 km into space and are sent up through cracks in the ice.
Similar disturbances in Jupiter’s magnetic field were found around Ganymede, and in that case the Hubble telescope has also detected traces of water molecules in the thin vapor atmosphere, thus strengthening the suspicion of water.
Last but not least, Callisto also seems to disrupt the giant planet’s magnetic field, although the evidence for water under the ice is not as strong there as on the other two moons.
On all the globes, the vaporosphere is too thin for liquid water to remain on the surface, but the effects of Jupiter’s gravity could cause water to be liquid beneath the ice sheet.
In the same way that the Earth and the Moon pull on each other, Jupiter’s gravitational pull on its moons is so powerful that there is a tidal effect that heats the interior of the ice mass above the melting point.
Water and life are connected
Astronomers’ interest in liquid water stems from the fact that here on Earth life can be found everywhere where water is in liquid form. Even at great depths, there are hot springs that release into the environment heat, minerals and salts that are essential for living things.
It may be that the three moons have terrestrial activity just like on Io but at the bottom of the oceans and not on the surface. Then there could be similar heat sources as are known on the ocean floor on our own planet.
Jupiter’s moons are wet
At NASA, humans have found definitive proof that Europa, Jupiter’s moon, has an entire ocean of liquid water that could harbor life.
In its data acquisition, JUICE gets better than one chance at each moon. During the three years that the spacecraft will be in orbit around Jupiter, it will pass close to these moons 30 times.
It is hoped that the spacecraft’s magnetometers will provide definitive evidence that oceans exist on these three moons.
The spectrometers are also supposed to sniff out what kind of molecules can be found in the atmosphere, but for example on Europe they can come from water eruptions.
The planet Callisto will be visited 12 times and JUICE will then go down to an altitude of 200 km. In such a detour, one should also investigate why carbon dioxide, oxygen and hydrogen seem to be found in the thin atmosphere, but these gases seem to be in constant renewal.
Radar sees through the ice
At Ganymede, JUICE is to conduct detailed research as the spacecraft completes its journey by entering a stable orbit around this moon at an altitude of 500 km. From there, there is enough time to gather information about the surface, the vaporosphere and what is below the surface.
Ganymede is 5,260 km in diameter, the largest moon in the solar system and even larger than Mercury. Orbiting Ganymede, the JUICE spacecraft is to peer below the icy surface for the first time.
Among the instruments in the spacecraft is the radar RIME, which can detect down to a depth of 9 km. It is true that the ice sheet is much thicker, but the device is unable to see cracks that extend so far up and presumably contain water.
If so, the radar measurements can finally confirm that Ganymede is not a bottomless ice globe.
The JUICE spacecraft will orbit Ganymede for about a year, periodically using the rocket engine to maintain the correct altitude. By the end of 2035, the fuel will run out, after which JUICE will lose altitude and eventually crash to the surface.
But when that time comes, the spacecraft will hopefully have sent scientists enough data to provide answers to many questions about a possible ocean beneath the ice.
Otherwise, people will have to make do with the information from another spacecraft that will reach Jupiter in 2030.
It is the NASA spacecraft Europa Clipper that will be launched in 2024 and is supposed to go close to Europa several times, where the intention is to find traces of salts, amino acids, carbon, oxygen, sulfur and other basic units of life.
The other large moons of Jupiter will be in the middle of the whirlwind of space research in the next decade, and it is quite possible that it is precisely there that definitive evidence will finally be found that life can be found on distant planets and is completely independent of life on Earth.
