JUICE: The messenger sent to explore Jupiter's icy moon has set off!

Produced by: Science Popularization China

Author: Li Zhenzhen (Shanghai Astronomical Observatory, Chinese Academy of Sciences) Sui Yuan (Shanghai Northland School)

Producer: China Science Expo

At 20:14 Beijing time on April 14, 2023, the European Space Agency (ESA) successfully launched the Jupiter Icy Moons Explorer (JUICE) from the French Guiana Space Port on an Ariane 5 launch vehicle.

According to the plan, JUICE will arrive at the Jupiter system in 2031 after eight years of space travel. By then, JUICE will conduct exploration of Jupiter and its three icy satellites (Europa, Ganymede and Callisto), study Jupiter's atmosphere and magnetic field, the ice shell and compound composition on the surface of the icy satellites, and explore possible life on the icy satellites.

JUICE's spacecraft

(Image credit: ESA)

JUICE launch site

(Image credit: ESA/CNES/Arianespace)

Human exploration journey: from looking from afar to visiting

As one of the celestial bodies that is most easily visible to the naked eye, Jupiter was discovered very early, but the satellites around Jupiter are difficult to be seen directly with the naked eye.

In 1610, Italian astronomer Galileo pointed his homemade telescope at Jupiter and discovered for the first time that there were four satellites around Jupiter. This discovery (other planets besides Earth also have satellites) had a huge impact on people's cognition at the time and promoted the germination and development of scientific thought.

To pay tribute to the great scientist Galileo's feat, a plaque commemorating Galileo was specially installed on the back of the JUICE spacecraft launched this time.

Through telescope observations, people have learned a lot about Jupiter and its satellite system. Jupiter is the largest planet in the solar system (equivalent to 1,321 Earths) and the heaviest (2.5 times the mass of the other seven planets combined). Its huge mass means that Jupiter has a large number of satellites (92 are known so far). Among them, Io, Europa, Ganymede and Callisto were discovered by Galileo in his early years and were later called Galilean satellites; the other satellites are much darker and require larger telescopes to be seen.

Today, our understanding of the Earth's neighbor, the Jupiter system, is no longer limited to observing it from afar through telescopes on Earth. Instead, we can "pay a visit" to Jupiter by launching probes, conduct on-site surveys, and transmit the local conditions back to Earth via radio.

In recent decades, humans have conducted many explorations of Jupiter by launching a series of spacecraft. These explorations began in the 1970s with NASA's Pioneer program. The explorations still underway include NASA's Juno and Europa missions, and the European Space Agency's Yos.

Timeline of Jupiter Exploration Progress

(Image credit: ESA; Chinese translation added by the author)

These probes have greatly enriched people's understanding of Jupiter and its satellite system. These messengers sent to Jupiter described the following information to us: Jupiter is mostly liquid and gaseous, with an extremely variable atmosphere, large-scale thunderstorms, and a strong magnetic field; Jupiter's satellites have signs of liquid water oceans, groundwater, and active volcanoes. These signs suggest that Jupiter and its surrounding satellites may have habitats suitable for the survival of life.

JUICE's trip planning

According to the plan, after its launch, JUICE will enter Jupiter's orbit in July 2031 and enter the orbit of Ganymede at the end of 2034. This will be the first time that a human spacecraft has orbited a satellite other than our own.

JUICE's trip planning to the Jupiter system

(Image credit: ESA; Chinese translation added by the author)

JUICE will not fly directly to Jupiter, but will take a tortuous journey. JUICE will fly over multiple planets and satellites along the way, using the gravity of these celestial bodies to change the flight trajectory and gain acceleration to save fuel for the spacecraft.

Artist's impression of JUICE's flight to the Jovian system

(Image credit: ESA)

The distance between Jupiter and the Sun is about five times that between the Sun and the Earth. The solar energy received around Jupiter will be much less than that received on Earth. In order to obtain as much solar energy as possible, the spacecraft carrying JUICE has a huge solar panel of 85 square meters, which is the largest solar panel ever built for an interplanetary spacecraft.

Finally, JUICE will be destroyed on Ganymede after completing its historical mission.

JUICE's Equipment and Skills

JUICE weighs about 6 tons and carries a variety of scientific instruments including optical cameras, mass spectrometers, radar detectors and magnetometers. It will conduct multi-faceted exploration of Jupiter and its icy satellites.

The mass spectrometer carried by JUICE will detect the atmospheric surface and interior of Jupiter's three satellites. When seawater is ejected from cracks in the ice shell of Jupiter's satellites, JUICE will take real-time samples and analyze the organic molecules that may indicate the existence of life.

JUICE collects seawater ejected from the ice shell of Jupiter's satellites

(Image credit: ESA)

The radar carried by JUICE can penetrate ice layers at least 9 kilometers thick. If the ice shell on the surface of the satellite is thin enough, the radar may detect an ocean under the ice shell, or at least detect underground water pockets embedded in the ice. The eruption of these underground water pockets may be the reason for the cracked landscape on Jupiter's satellites.

Schematic diagram of JUICE detecting the ice shell on the surface of Jupiter's satellites

(Image credit: ESA)

JUICE's scientific mission

JUICE will focus on addressing five key scientific questions.

1. What are the ocean worlds of Jupiter's satellites like?

There are three moons around Jupiter that may have large amounts of liquid water hidden beneath their icy crusts. How deep are these oceans? Is the ocean salty or fresh? JUICE will explore the icy crusts and hidden ocean layers of these moons to understand the conditions and mechanisms for their formation.

2. Why is Ganymede so unique?

Among Jupiter's three icy moons, Ganymede is the primary scientific goal of JUICE. Ganymede is the largest moon in the solar system and the only one with an intrinsic magnetic field.

Ganymede provides an ideal natural laboratory for studying the properties of icy worlds. JUICE will focus on this moon while comparing observations of Europa and Callisto. As the first spacecraft to orbit an icy moon, JUICE will use its suite of 10 advanced instruments to measure Ganymede's rotation, gravity field, shape, internal structure, magnetic field, and material composition. JUICE will also investigate water vapor and other materials in Ganymede's atmosphere to fully understand the processes occurring in the moon's space environment.

Artist's impression of JUICE's tour of the Jupiter system

(Image credit: ESA)

3. Is there life in the Jupiter system?

One of the core exploration goals of JUICE is to determine whether Jupiter's moons could provide an environment suitable for the existence of life.

Jupiter, as a gas giant, is not suitable for the existence of life, but there may be liquid water oceans under the ice shells of the satellites around Jupiter. As the largest satellite in the solar system, Ganymede can use its own magnetic field to shield space radiation. At the same time, Ganymede's gravitational interaction with Jupiter can obtain energy through tidal heating mechanisms. These environmental factors are exactly what life needs to survive.

Because of these environmental factors, people are full of expectations that there may be signs of life on this icy satellite. The environment of Ganymede's ocean may be similar to the environment of the deep seabed on our earth. Given that there is no sunlight on the deep seabed of the earth, but there are still organisms that rely on submarine volcanoes and hot springs to obtain energy, it is possible that there is life in Ganymede's ocean world.

JUICE will explore the hidden oceans, magnetic fields, heating processes, tidal effects, orbits, surface activity, core composition, atmosphere and space environment of Jupiter's three icy moons to determine whether the conditions necessary for life exist. JUICE's high-resolution positioning will help find the essential and important elements for life in the icy moon ocean world.

JUICE's research on the ice shells and compound composition of Jupiter's satellites even goes beyond research on the Jupiter system itself, because such research can help humans understand the general habitability of "ice and snow worlds" in the entire universe for life.

4. How do the complex environments of Jupiter and its satellites influence and shape each other?

Jupiter has a strong and unique gravity field, magnetic field and plasma environment. Understanding the complex magnetic environment of the planet remains one of the unsolved mysteries of the solar system and is a problem that JUICE aims to solve. JUICE will also study Jupiter's complex gravitational environment, understand the tidal interactions between Jupiter and its moons, and the relationship between the orbital dynamics of the moons.

Overall, JUICE will explore how different aspects of Jupiter's environment are coupled together. This can help us reveal more about not only our own solar system, but also other planetary systems in the universe.

5. What does a classic gas giant planet look like? How does it form and how does it function?

The Jupiter system is the prototype for gas giants in our own solar system and in many other star systems beyond our own. A major goal of JUICE is to understand how gas giant planets and their moons form and evolve.

Exploring the origin, history, and evolution of Jupiter and its satellites helps us understand how planetary systems evolve over time and reveals possible habitable environments for Jupiter systems around other stars.

Overall, the broader significance of JUICE's study of the Jovian system lies in understanding how planetary systems in general work like the Jovian system.

Conclusion

"There is no end to the exploration of the vast starry sky." From Galileo's discovery of Jupiter's satellite system through a telescope more than 400 years ago to the launch of probes to orbit Jupiter's satellites, human beings' understanding of the universe is constantly advancing. We hope that JUICE will successfully complete its scheduled scientific mission and send us new news about the world of Jupiter.

References:

【1】ESA. Juice-Jupiter Icy Moons Explorer[EB/OL]. [April 13, 2023].

【2】ESA. JOURNAL ARCHIVE of juice[EB/OL]. [April 13, 2023].