In 1610, the scholar Galileo aimed his improved telescope at Jupiter. There he was the first to see four moons: Io, Europa, Ganymede and Callisto. Four centuries later, the European Space Agency (ESA) will visit these moons, minus Io.
Space probe Jupiter Icy Moons Explorer, or Juice for short, will be launched from French Guiana on an Ariane-5 rocket at 2:15 p.m. Dutch time. For ESA, the stakes are high. In 2007, the organization ventured beyond Mars completely independently for the last time.
The main goal is to find out if life could have originated on the moons. “Juice has no instruments that can find life,” says ESA engineer Alessandro Atzei. What the probe does is accurately map the conditions on the moons. “Are there the ingredients for life? At least, as we know it.”
In any case, lunar Europe is a promising place. “We know that water is present in large quantities,” says Bert Vermeersen, professor of planetary exploration at TU Delft. “The oceans are even bigger than on Earth.”
The water is frozen on the surface, but there is an ocean below. Scientists also want to investigate the composition of the water because it is very important for the chance that life can arise.
Planet researcher Vermeersen is curious about the thickness of the ice layer. “If the ice is 20 kilometers thick, that’s not good news for a future mission that takes a drill,” he says. “We already have trouble reaching deep lakes 2 to 3 kilometers under the Antarctic ice.”
The ten instruments on board also measure other things, such as the composition of the atmosphere and radioactivity. Juice also has a camera.
Need patience
Scientific results do not only say something about our solar system. If the conditions on the moons around a gas giant like Jupiter are favorable for life, that also says something about the chance of life on planets around other stars. And many gas giants have been discovered there in recent years.
We have to be patient for the first results. Juice will not arrive at Jupiter until the summer of 2031. To build up speed, the probe must first swing four times from the Moon, Earth, and Venus; gravity assists – help from gravity – in space travel jargon.
That works like this:
At Jupiter, the probe will slow down to make dozens of flybys of the moons. Main destination is Ganymede, a moon larger than the planet Mercury. In 2035, Juice will go round in circles here and eventually crash.
Not only the flight plan, but also the construction was complicated. For example, the conditions on Juice’s route are extreme. At Venus, the probe heats up to 250 degrees Celsius. While he can later cool down to 230 degrees below zero. In addition, the magnetic field and radiation around Jupiter are extremely strong. Juice’s most sensitive electronics are therefore housed in a lead ‘safe’.
Distance is also a challenge. “It’s so far gone that Juice doesn’t immediately respond to commands,” says ESA engineer Atzei. “We use a lot of autonomous systems. Everything is pre-programmed.”
Because Jupiter is more than five times farther from the sun than Earth, the planet only gets 3 percent of the solar energy. Juice therefore has 85 square meters of solar panels – built by Airbus in Leiden – that are folded in half.
Other things to watch
In addition to the conditions for life, scientists also study the origin and development of the solar system. “Jupiter’s system is actually a kind of mini-solar system,” Atzei says. At the center is a gas giant with rocky moons surrounding it, as the Earth and other planets revolve around the sun. Knowledge about Jupiter’s system also helps to understand our solar system. And planetary systems around other stars.
For this research, scientists want to measure extremely accurately where the moons and Juice are located. They do this with the Dutch experiment PRIDE of TU Delft and the JIVE institute, known for the radio telescopes in Dwingeloo and Westerbork.
By tracking the probe’s signal with radio telescopes, they determine its speed and direction. In this way, the rising and falling of the ice on the moons can be followed indirectly. This happens under the influence of Jupiter’s immense gravity. With the GALA laser, an instrument involving planetary scientist Vermeersen, Juice measures the distance to the moons. Because it is known exactly where the probe and moon are located, researchers can measure the tide precisely.
NASA is also going
Juice is not the first mission to Jupiter. Not only did Voyager 1 and 2 of ESA’s American counterpart, NASA, fly past the planet; NASA’s Galileo and Juno missions had the planet as their final destination.
Juice is not alone between 2031 and 2035 either. NASA will launch the Europa Clipper in 2024, a probe that will explore the moon Europa. Despite its later launch, the Clipper arrives a year ahead of Juice. That’s because NASA uses a more powerful rocket.
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