What a newly-launched probe can teach us about Jupiter and its icy moons

The Jupiter Icy Moons Explorer mission (JUICE) launched on Friday to boldly go where few spacecrafts have gone before: Jupiter. 

As the largest planet in the solar system, Jupiter has more than 60 moons orbiting it, and the European Space Agency’s (ESA) JUICE spacecraft will study three of its largest in detail. 

These three Jovian moons — Ganymede, Callisto, and Europa — are believed to harbor subsurface oceans, which could mean they also contain life. But to find out whether they actually do, the spacecraft will need to explore and analyze these moons. 

The answers it uncovers will not only help characterize the moons and the likelihood they support life, but also will help shape future missions to Jupiter and other gas giants. 

The road to the outer solar system is long, which means the JUICE spacecraft won’t arrive at Jupiter until 2031. To get there, it is going to need more umph than its Ariane 5 rocket can provide. The spacecraft will need to slingshot itself around other planetary bodies to get a boost and tweak its trajectory. 

Its first gravity assist will come in 2024, when the craft will use the moon’s and Earth’s gravity to put itself on course for Jupiter. In 2025, the craft will complete the first of three planned planetary flybys, as it whizzes around Venus, gaining even more momentum. Finally, it will fly by Earth two more times (once in 2026 and once in 2029), setting it up for an on-time arrival at Jupiter in 2031. 

When JUICE is at its destination, the craft will begin its science phase, conducting multiple flybys of Ganymede, Callisto and Europa, before it begins orbiting Ganymede, the largest moon in the solar system, even larger than the planet Mercury. 

The probe will spend four years conducting science and using a suite of 10 state-of-the-art instruments to classify the moons, peer beneath their surfaces and determine their habitability. 

The mission will work in parallel with NASA’s Europa Clipper mission, which is slated to launch in 2024 on a mission to study the Jovian moon Europa in detail. These two missions are the first to explore moons other than our own.

JUICE will concentrate most of its mission on Ganymede while NASA’s Clipper mission will explore Europa. 

JUICE will only fly by Europa twice, coming within 250 miles (400 kilometers) of the moon’s surface, while Clipper will make regular dives coming within a few dozen miles of Europa’s surface. 

Any spacecraft orbiting Jupiter and its moons must be careful as the planet’s powerful magnetic field could damage anything that hangs around for any extended period.

Only two other spacecraft have explored Jupiter: Galileo from 1995 to 2003, and more recently, the Juno spacecraft which has been circling the giant planet since 2016. During its mission, Galileo discovered that three of Jupiter’s main moons may have liquid water lurking under the surface. The spacecraft also discovered that Ganymede has its own magnetic field, making it the only known moon in the solar system with this characteristic. 

Data collected from Galileo indicated that storms on Jupiter were so massive that they could be larger than the Earth. The Juno spacecraft has spent time studying these atmospheric storms in more detail, indicating that Jupiter’s atmospheric weather is complex and extends far beyond the visible clouds we see swirling on its surface. 

Jupiter is a gas giant, but the Juno mission discovered the planet may have a heavy metal core underneath. 

Scientists are hoping JUICE will be able to shed some light on Jupiter and help to deepen our understanding of the Jovian system and its habitability. 

According to Christian Erd, a JUICE spacecraft and system manager, one of the overarching goals for this mission was to show that this dynamic environment surrounding Jupiter was not completely out of reach for a spacecraft. 

“Spending three and a half years at Jupiter is equivalent to the radiation exposure of a telecommunications satellite in geostationary Earth orbit for 20 years, which we have plenty of experience managing,” he said. 

Erd says that just two orbits of Europa will add up to one-third of the mission’s whole radiation budget, which is why the spacecraft will concentrate more on the other two moons, conducting 21 flybys of Callisto, Jupiter’s second largest moon. Its heavily cratered surface is a stark contrast to Europa, which is known to have plumes of water emanating from its surface. The spacecraft is scheduled to conduct 12 flybys of Ganymede before it begins its orbit of the massive moon. 

Scientists are pretty sure that both Europa and Ganymede have oceans of liquid water under their surface, and while they suspect the same is true of Callisto, they’re hoping the JUICE mission will help prove it. 

“The Galileo mission measured weird disturbances on the magnetic field around Jupiter, which some scientists have attributed to the movement of liquid inside the moons,” said Olivier Witasse, a project scientist on the mission. “If you are able to measure variations of the magnetic field around each moon, you could attribute the variations to the presence of a subsurface liquid which could be as deep as 200 kilometers [120 miles ] underneath the crust.”

Observations of water vapor made by the Hubble Space Telescope back up the magnetic field observations, further indicating that both Europa and Ganymede have subsurface oceans. Juice is expected to help confirm that as well as shed some light on Callisto’s interior. Scientists believe that the surface we see on Callisto is one of the oldest in the solar system and has not changed much since its formation.

“Callisto formed 4 billion years ago when Jupiter formed and the surface, we see is from the time that it was born,” Witasse said. “In stark contrast, Europa has a very active surface, which is only 50 million years old and is resurfacing all the time.” 

Witasse said that JUICE could help tell us what if anything is going on in Callisto’s interior and why Ganymede is the only moon in the solar system to have its own magnetic field. It will also study Jupiter’s atmosphere in more detail, providing clues on its chemical composition and weather patterns. 

“By studying [Jupiter] and its moons in more detail, scientists are hoping to learn more about how the solar system and exoplanetary systems work, how planets form around other stars, and are hoping to use Jupiter as a model for other star systems,” officials from ESA said before the launch.” 

Of the three, Europa is the best candidate to find life, but scientists say they are prepared to not find any at all, especially on Ganymede. 

“We know that the ocean on Europa is in contact with a rocky substrate, which means it’s similar to oceans we have here on Earth,” Witasse said. “As such, there might be some interesting reactions and hydrothermal activity on Europa, just like we see at the bottom of oceans on Earth.”

Juice will search for evidence of the building blocks of life, including elements like carbon, oxygen, nitrogen, iron and magnesium. However, scientists are confident that we won’t see any on Ganymede, even if the moon has a subsurface ocean. That’s why, at the end of the mission, in late 2035, the Juice spacecraft will crash land on the surface of the moon.

Unless of course, they make a surprising discovery along the way.