Next week, Europa will fly its first mission to the Jupiter system to explore the gas giant and three of its intriguing moons.
The European Space Agency (ESA)-led Jupiter Icy Moons Explorer spacecraft, or JUICE, will launch on Thursday (April 13) from Europe’s spaceport in French Guiana. JUICE, packed with what ESA describes as (opens in new tab) “the most powerful payload ever flown to the outer solar system,” was newly cocooned inside Ariane 5 rocket that will fly it into space.
This “means we have seen the spacecraft for the last time ever,” ESA announced on the mission Twitter (opens in new tab) account on Wednesday (April 5). “And that we are one step closer to launch!”
Related: Europa’s flagship JUICE mission will study Jupiter’s moons Europa, Callisto and Ganymede.
Shortly after liftoff, JUICE will separate from the rocket, fan out its solar panels and kickstart its 7.6-year cruise to the largest planet in the solar system.
During its time in the Jovian system, JUICE’s main goal will be to study Jupiter and three of its largest moons: Europe, Callisto and Ganymede. The spacecraft has no lander, so it won’t land on any of its targets, but it will fly past all the moons multiple times to collect valuable data.
Between 2021 and 2034, JUICE will only whiz by Europa twice, skimming as low as 400 kilometers above the moon’s surface. The spacecraft will also whiz by Jupiter’s second-largest moon Callisto 21 times and complete 12 flybys of Ganymede, according to mission launch kit (opens in new tab).
In 2034, the spacecraft will enter orbit directly around Ganymede, making it the first moon other than Earth’s to have a spacecraft in its orbit. The mission will self-destruct a year later by crashing into Ganymede’s surface.
“[The moons] are special in the sense that we think they contain large oceans of liquid water, which is quite fascinating, Olivier Witasse, project scientist for the JUICE mission, told Space.com.
Primarily, JUICE will collect data to confirm the presence of such liquid water – crucial to life as we know it – beneath the surface of these moons, which was only hinted at by the Galileo mission in the 20th century.
“I’m really looking forward to seeing the results after we arrive [the] destination in 2031,” Witasse said. “I’m just curious and patient (I have to [be]!)”
Related: Jupiter’s Galilean Moons (Images)
Ganymede: A Uniquely Complicated World
Ganymede, the largest moon in the solar system, will be JUICE’s defining science target, and for good reason.
Ganymede has a radius of 1,635 miles (2,631.2 km), which is only slightly smaller than Mars, and is 4.5 billion years old, placing it the same age as its parent planet. Scientists believe that the moon was formed from gas and dust left over from the formation of Jupiter, and the fact that it has been around since early in the solar system’s history makes it of enormous scientific value.
Back in 1996, when the Galileo spacecraft ventured just 264 miles (264 km) above Ganymede’s surface, scientists confused to discover (opens in new tab) its distinct planet-like magnetic field. So far, Ganymede is the only moon in the solar system known to boast its own magnetic field.
As Ganymede orbits Jupiter – which has its own massive magnetic field – from 665,000 miles (1 million km) away, the moon’s magnetic field is partially submerged in the gas giant’s. This interaction is complex and unique, triggering puzzling phenomena on the Moon, such as the dancing auroras that “rock back and forth” in response to changes in Jupiter’s magnetic field.
Ganymede is also unique in hosting a surface that betrays its history of billions of years. Besides having largest impact crater among all solar system bodies, the moon is scarred with numerous craters, denting 40% of its surface. The remaining 60% is filled with countless tracks crossing thousands of miles.
Also, its subsurface oceans likely have more water than Earth’s, and scientists recently found that younger parts of the moon could have been formed by a certain flood on its surface.
Together, this variety of equally aged surface features makes the Moon a scientific hunting ground for learning about the history of the surface as well as its past and present geologic activity.
Ganymede’s subsurface ocean is believed to be sandwiched between layers of ice, making it unlikely to host the moon alien life, scientists say (because there probably isn’t much interesting chemistry going on in that water). So the JUICE team is confident that ramping the spacecraft onto Ganymede’s surface at the end of the mission will not contaminate a habitable world. And this action will protect another moon that is considered more friendly to life – Europa.
Related: The 6 Most Likely Places for Alien Life in the Solar System
Europe: “A Cracked Egg”
Europa may be the smallest of Jupiter’s four main moons, discovered by famous 17th-century astronomer Galileo Galileibut it is considered one of the best places for alien life to sprout.
Europa, unlike Ganymede, is relatively active, thanks to its proximity to Jupiter. Because of that proximity, the gas giant has significant gravitational influence on Europa, which can be seen in the moon’s large tides that stretch and compress its frozen surface. Sometimes such activity cracks its youthful surface, which scientists believe is only 20 million to 180 million years old, forming fissures and ridges that stretching hundreds of miles and overlap to form their own intricate design.
Such features are seen as lines that “scratch” the surface of the moon, which scientists believe may also host salt taken from the underground sea believed to be 40 to 100 miles (60 to 150 km) deep. This newly surfaced salt is bombarded with radiation, giving it a signature reddish-brown color, but the process that leads to this mysterious material is not well understood.
Perhaps the most fascinating aspect of Europa is the occasional glimpse it provides of a global ocean hidden beneath its 15-mile-thick (20 km) icy surface. In recent years, researchers have think they have discovered evidence of sporadic plumes of water erupting from the moon’s frigid surface. Such plumes, which can rise 120 miles (200 km) high, are believed to come from the moon’s hidden oceans. But scientists know little about the processes that drive these mechanisms in the oceanic world.
Europa’s frozen surface also has pools of meltwater, which scientists think could be “cozy living environments” for alien life. And its oceans are believed to be in contact with its rocky core, allowing a host of complex chemistry to occur.
Related: Europa Clipper: A Guide to NASA’s New Astrobiology Mission
The geologically dead Callisto
Jupiter’s second largest moon Callistowhich is almost the size of Mercury and has 142 known craters that mark its surface, is among the most battered moons in the solar system.
Unlike Europa’s surface, which is young thanks to the moon regularly recycling its surface, Callisto was once thought to be a “ugly duckling moon“, due to the dormancy of its 4.5-billion-year-old surface.
Countless asteroid impacts have punctured Callisto’s surface, and the resulting craters haven’t changed much since they began accreting 4.5 billion years ago. For example, the earth heals itself through recycle its surface continuously through plate tectonics. Callisto, on the other hand, cannot do the same, so the moon was long considered a boring place to explore, let alone search for alien life.
Although there are no water plumes erupting from Callisto’s surface, scientists believe the moon hosts a salty ocean beneath its punctured surface. They found this thanks to data collected by the Galileo spacecraft, which put the moon back on the map of interesting worlds in the Jupiter system to explore.
A second mystery involving Callisto is its mysterious ability to continuously replenish its atmosphere, which is dominated by carbon dioxide but is apparently so thin that individual gas molecules “literally drift around without bumping into each other,” NASA’s Robert Carlson, who was the principal investigator of the Galileo spacecraft’s instruments, said then. Because the atmosphere is so weak, it is easily dispersed into space, but scientists don’t yet know how the moon seems to replace it time and time again.
Unsolved puzzles about Jupiter
You might think we know all we need to know about Jupiter, the largest planet in the solar system. But scientists actually know very little about the evolution of the gas giant, whose thick atmosphere and absence of a solid surface lead to interesting but puzzling phenomena.
For example, Jupiter has strong auroras at its north and south poles. Scientists have been studying these Jovian lights for at least four decades, but they still don’t fully understand how they are created. The gas giant’s ability to host multiple life-friendly moons in its system is also one of the unsolved mysteries, one that the JUICE mission will try to unlock.
To carry out its explorations of the Jupiter system, JUICE carries an array of 10 complex and sensitive instruments. From a technical point of view, building JUICE was not easy, Witasse told Space.com. Preparing the spacecraft, which needs a lot of fuel to navigate, to be robust enough to face Jupiter’s strong and dangerous radiation is no small feat. Part of the mission’s development occurred during the pandemic, adding to the complications for the JUICE team.
“But all in all, we succeeded, and we’re ready to launch,” Witasse said.
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