JUICE Mission: Unlocking Jupiter’s Icy Moon Secrets

The Jupiter Icy Moons Explorer (JUICE) probe is on its very long journey to Jupiter. It won’t be until after this decade is over that the spacecraft will finally arrive at the King of Planets.

Once reached, ESA’s mission will focus on Jupiter’s “big three” icy moons: Europa, Ganymede, and Callisto. Jupiter actually has 101 known moons, as of March 2026, so while mapping Ganymede’s magnetic field, JUICE will also observe other moons.

A recent paper called “Io and the Minor Jovian Moons – Prospects for JUICE¹,” published in Space Science Reviews by researchers from the German Aerospace Center (DLR), detailed how the spacecraft could still gather valuable observational data on Io and Jupiter’s lesser-known moons despite not directly targeting them. The paper outlines opportunities to study volcanic activity, surface changes, and dust environments through distant imaging and flyby geometry.

To understand why these observations matter, we need to examine Jupiter’s extreme environment and the moons JUICE will study.

JUICE: Expanding Science Beyond Its Primary Targets

The Solar System’s Dominant Force and Cosmic Architect

Jupiter is believed to be the first planet to have formed in the solar system and is the fifth planet from the Sun. Often called the “King of Planets,” it formed from the dust and gases left over from the formation of the Sun.

With a radius of 43,440.7 miles (69,911 kilometers), it is the largest planet in the solar system. In fact, Jupiter is so large that it could fit about a thousand Earths inside it if it were hollow. It also has the shortest day in the solar system, taking just 9.9 hours to complete one rotation. But because Jupiter spins almost upright, it doesn’t have as extreme seasons as other planets do.

As for its signature stripes, the dark orange bands are called belts, while the lighter ones are called zones, which flow in opposite directions. These stripes are cold, colorful, and windy clouds of ammonia and water that float in an atmosphere of hydrogen and helium.

Jupiter is actually mostly just these swirling gases and liquids, with no true surface. However, deep within the planet, hydrogen exists in a liquid state, forming what is effectively the largest “ocean” in the solar system. And halfway to its center, scientists believe the liquid is electrically conducting due to pressure, and the planet’s fast rotation and internal electrical currents together generate its powerful magnetic field.

This powerful magnetic field accelerates charged particles in Jupiter’s vicinity and creates intense radiation that even degrades spacecraft electronics rapidly.

Despite this extreme radiation environment, which makes Jupiter itself inhospitable, several of its moons may still support conditions suitable for life. The planet has four large moons: Io, Europa, Ganymede, and Callisto, which are known as the Galilean satellites, plus many smaller moons, creating a sort of mini solar system of their own.

Among the large moons, Ganymede is the largest in the solar system, even bigger than the planet Mercury, while Io is the most volcanically active body. A few small craters of Callisto, meanwhile, suggest some current surface activity. Then there’s Europa, which has a water ocean beneath its frozen crust.

To investigate these questions in greater detail, ESA launched the Jupiter Icy Moons Explorer (JUICE).

A Multi-Year Quest to Uncover Habitable Worlds Around Jupiter

The first major operation in the ESA Cosmic Visions 2015-2025 program was successfully launched in April 2023 from Europe’s Spaceport in French Guiana.

JUICE is a single-orbit spacecraft with no lander but 10 scientific instruments, including cameras, sensors, radar, and magnetometers, to analyze the moons and their potential to host life.

To protect the spacecraft’s instruments from Jupiter’s harsh environment, JUICE has been fitted with elaborate radiation shields. It is also equipped with massive solar panels to generate electricity for powering the spacecraft.

With Jupiter much farther from the Sun (over five times farther than Earth), the spacecraft receives far less solar radiation. To generate sufficient power, scientists are using panels as large as 914 square feet. Each wing is shaped like a cross and must work at low temperatures in its high-radiation environment.

Once JUICE reaches the gas giant in July 2031, it will take another three years before it moves into Ganymede orbit in December 2034.

This makes JUICE a critical step toward improving our understanding of the Jupiter system, located about 750 million kilometers from Earth on average. Once in orbit, JUICE will become the third spacecraft to study Jupiter from orbit.

The first was the Galileo probe, which studied Jupiter between 1995 and 2003 and found evidence that liquid-water oceans may exist beneath the ice crusts of three of its four main moons. Besides finding storms in Jupiter’s atmosphere to be potentially larger than Earth, the mission found that Ganymede has its own magnetic field, making it the only known moon to possess one.

The second was Juno, which has been circling the gas giant since 2016. This mission found that Jupiter’s atmospheric weather layer extends beyond the visible clouds and may contain a core of dilute heavy metals.

While profoundly successful, these missions have uncovered only the tip of the iceberg, and many questions about Jupiter and its moons remain unanswered.

JUICE is designed to extend these discoveries by directly probing the structure, composition, and habitability of Jupiter’s icy moons. JUICE has already performed its first Earth flyby back in August 2024.

After arrival, the spacecraft will spend three years orbiting the planet and making close flybys of its three moons before moving into orbit around Ganymede. By that time, NASA’s Europa Clipper mission will already be there. Launched a year before JUICE, Europa Clipper will arrive at Jupiter slightly before ESA’s mission.

Unlike JUICE, whose focus is on Ganymede and the less-explored Callisto, the Europa Clipper spacecraft will be making regular dives on the lively Europa. It will analyze the habitability of the smallest of Jupiter’s four Galilean moons, which features an ice-covered surface with strong evidence of a subsurface saltwater ocean containing twice as much water as Earth’s oceans.

JUICE will also make two flybys of Europa. But more importantly, it will make 21 flybys of Callisto, which is the second-largest and most distant of the four main Jupiter moons. It will come as close as 120 miles to its surface and will help unveil whether Callisto also has a subsurface ocean.

Observations by ground-based telescopes and the Hubble Space Telescope have already provided more evidence for the presence of liquid water oceans on Ganymede and Europa, and even water vapor has been detected in their atmospheres.

After performing 12 flybys of Ganymede, JUICE will enter Ganymede’s orbit, which falls between the orbits of Callisto and Europa.

JUICE’s Distant Opportunity to Observe Io’s Violent Volcanism

Io is a planet-sized moon of Jupiter that was first discovered in 1610, along with the other three moons, by Galileo Galilei.

Among Jupiter’s four large moons, Io is the innermost, and while second-smallest among them, it’s still a bit larger than our moon. Of all the natural satellites, it actually has the strongest surface gravity.

While its diameter and distance to the central planet’s “surface” are comparable to the respective values for Earth’s Moon, its orbital speed is 17 times faster and the revolution period 15.5 times shorter because of Jupiter’s much stronger gravity. Due to Io’s orbit plane lying almost exactly in the Jupiter equatorial plane, the moon experiences solar eclipses.

These extreme orbital dynamics have direct consequences for Io’s interior. What makes Io really interesting is that it is the most geologically active object in our solar system. There are more than 400 active volcanoes on Io that constantly resurface the moon. This extreme geologic activity is due to tidal heating from friction within its interior as Io is pulled by Jupiter, Europa, and Ganymede.

These active volcanoes discharge magmatic materials in both horizontal and vertical directions, which gives Io a colorful appearance.

Despite this intense activity, Io is not a primary target of the JUICE mission. However, JUICE will still conduct distant monitoring of volcanoes, especially in the polar regions, which are very hard to observe from Earth.

As the latest study noted, the objectives for the JUICE mission at Io include characterizing the composition of the moon’s surface, monitoring volcanic and plasma activity, along with radio emissions from 1 kHz to 45 MHz in its environment. It will also observe Io at spatial resolutions of 200 km and the plasma torus at 2000 km.

Despite this distance, the spacecraft will still track as much information about Io as it can.

To capture these phenomena, JUICE relies on a suite of specialized instruments. Its JANUS camera, which is the ‘eye’ of the mission and will provide high-res multispectral images of Jupiter’s moons, will monitor Io’s surface changes at about 6-12 kilometers per pixel. It will also observe Io’s sodium cloud, the aurora, and the interactions with Jupiter’s magnetosphere.

Furthermore, the camera will watch for hot spots and plumes that may have been missed by other missions like Juno, which recently observed the largest eruption that’s ever recorded on Io’s surface. The eruption emitted 80 trillion watts of energy.

Recently, for the first time, the James Webb Space Telescope (JWST) also detected sulfur in Io’s atmosphere, providing a way to track how volcanic gases escape into the massive magnetosphere of Jupiter.

MAJIS, the Moons and Jupiter Imaging Spectrometer, will observe Io at spatial scales between 60-100 km/px and will be able to identify species like SO, SO2 gas, SO2 frost, S2, NaCl, KCl, Fe-bearing salts, FeS2, silicates, or iron sulfides.

JUICE’s Ultraviolet Imaging Spectrograph (UVS), which will split and analyze the ultraviolet radiation reflected from Jupiter and its moons, will also observe auroras and SO2 emissions. The instrument was provided by NASA for the JUICE mission.

Meanwhile, its Particle Environment Package (PEP) will track Io’s plasma torus, a donut-shaped ring of ionized gas supplied by volcanoes’ outgassing. PEP contains sensors to identify Jupiter’s plasma environment.

The mission team at ESA has actually formed a joint committee with NASA to coordinate observations of the plasma torus on Io.

Beyond Io itself, JUICE also presents an opportunity to study Jupiter’s smaller inner moons. There are four smaller Jovian moons named Amalthea, Thebe, Metis, and Adrastea inside Io’s orbit. These small inner moons orbit Jupiter in a very narrow space between Io’s orbit and the planet’s cloud tops. Because of their small sizes and non-spherical shapes, they are also referred to as minor moons.

Living deep within Jupiter’s radiation belt, these moons hold their own scientific mysteries.

Amalthea, for instance, has low density despite being close to the “King of Planets.” This suggests that Amalthea may be extremely porous or contain a lot of water ice.

We may get better insight into these mysteries and the composition of these tiny moons through detailed spectrographic images captured by JUICE.

Many of Jupiter’s moons are actually farther than the scientific targets of JUICE, revolving around the planet outside the orbit of Callisto. But the likes of Himalia, the largest Jovian Irregular, and Kallichore may get some attention from the mission. Currently, no close flyby is planned for these objects, except for JXLIV Kallichore, which is under investigation. The spacecraft will only go as close as one million km to Kallichore, about 450,000 km to Thebe, and 400,000 km to Io.

The JUICE mission will approach Jupiter and orbit the planet over a four-year period from January 2031 to late 2034. With its close proximity to the Jovian moons, unique viewing perspective, and observation time, “JUICE will take a key role in the early 2030s for observations of Io, the small inner moons of Jupiter, and the Jovian Irregulars,” stated the study, adding “The expected data set is likely to remain unique for a long time to come.”

Investing in Space Exploration

Although JUICE is led by ESA and built primarily by Airbus, NASA and U.S.-based institutions have contributed key instruments and subsystems, including radar electronics, instrumentation components, and the Ultraviolet Spectrograph (UVS).

For investors seeking exposure to space exploration, Northrop Grumman Corp (NOC -1.88%) stands out for its deep involvement in satellite systems, advanced components, and scientific payload technologies. Its expertise in sensors, electronics, and deep-space infrastructure makes it a key player in interplanetary exploration efforts.

Northrop Grumman was actually the prime contractor for NASA’s JWST, leading design, construction, and integration of the observatory.

The global aerospace and defense technology company operates through a few key segments, including Aeronautics Systems, Space Systems, Mission Systems, and Defense Systems.

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From a financial perspective, the company has also delivered strong performance. Northrop Grumman, with a $96.5 billion market cap, has an EPS (TTM) of 29.08 and a P/E (TTM) of 23.38. It pays a dividend yield of 1.36%.

As for its financial position, the company reported a 10% increase in Q4 2025 sales to $11.7 billion. Sales for the year came in at $42 billion, up 2%. Meanwhile, net earnings totaled $1.4 billion, or $9.99 per diluted share for 4Q25 and $4.2 billion, or $29.08 per diluted share for the full year.

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Latest Northrop Grumman Corp (NOC) Stock News and Developments

Conclusion

The JUICE mission represents humanity’s most direct attempt to answer a fundamental question: are we alone? By the mid-2030s, when JUICE enters Ganymede’s orbit, we may have definitive answers about subsurface oceans on multiple moons, vast reserves of liquid water, and the chemical conditions necessary for microbial life. The data JUICE returns will not merely reshape our understanding of planetary systems. It could redefine what we consider habitable space in the universe.

Click here for a list of the top five places alien life may exist in the solar system.

References

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