As of April 30, 2025, the International Astronomical Union (IAU) recognizes 97 confirmed moons orbiting Jupiter. This number is not fixed because discoveries are ongoing, some moons are only provisionally designated, and a few have been lost and later rediscovered. Jupiter’s moon system is a dynamic and growing family of worlds ranging from small captured asteroids to the massive Galilean moons.
Key Takeaways: How Many Moons Does Jupiter Have?
- Jupiter has 97 confirmed moons as of April 30, 2025. However, there may be around 600 moons measuring at least 800 meters (2,600 feet) in diameter.
- The number changes frequently due to ongoing discoveries, confirmations, recoveries, and naming processes.
- The Galilean moons (Io, Europa, Ganymede, Callisto) dominate the system in terms of mass.
- Moons are grouped into inner regular, Galilean, prograde irregular, and retrograde irregular categories.
- Jupiter regained the lead over Saturn in 2023 but may lose it again as discoveries continue.
- Some moons are visible with binoculars or a small telescope.
- Several spacecraft have explored or will explore Jupiter’s moons in detail.
Table of Selected Moons
Jupiter’s moons vary widely in size, distance, and orbital characteristics. While the planet hosts 97 confirmed satellites, a handful dominate in size and scientific interest. The table below highlights a representative sample, showing the diversity from large, geologically active worlds to tiny, irregular bodies.
| Name | Diameter (km) | Orbital Distance (km) | Orbital Period (days) | Discovery Year | Discoverer(s) |
|---|---|---|---|---|---|
| Io | 3,643 | 421,800 | 1.77 | 1610 | Galileo Galilei |
| Europa | 3,122 | 671,100 | 3.55 | 1610 | Galileo Galilei |
| Ganymede | 5,268 | 1,070,400 | 7.16 | 1610 | Galileo Galilei |
| Callisto | 4,820 | 1,882,700 | 16.69 | 1610 | Galileo Galilei |
| Amalthea | 167 | 181,400 | 0.50 | 1892 | E. E. Barnard |
| Himalia | 170 | 11,460,000 | 250.6 | 1904 | C. D. Perrine |
| Elara | 86 | 11,416,000 | 259 | 1905 | C. D. Perrine |
| Metis | 40 | 128,000 | 0.30 | 1979 | Voyager Team |
| Adrastea | 20 | 129,000 | 0.30 | 1979 | Voyager Team |
| Thebe | 100 | 221,900 | 0.68 | 1979 | Voyager Team |
| Thyone | ~3 | 21,605,000 | −603 (retrograde) | 2001 | S. S. Sheppard et al. |
Table of All Known Moons
Here is the list of the 97 formally recognized moons. But, the planet likely hosts many more tiny moons.
| # | Name | # | Name | # | Name | # | Name |
|---|---|---|---|---|---|---|---|
| 1 | Metis | 26 | S/2016 J 1 | 51 | Aoede | 76 | S/2022 J 2 |
| 2 | Adrastea | 27 | S/2017 J 3 | 52 | Autonoe | 77 | Kore |
| 3 | Amalthea | 28 | Orthosie | 53 | Callirrhoe | 78 | S/2021 J 3 |
| 4 | Thebe | 29 | Eupheme | 54 | Chaldene | 79 | Eukelade |
| 5 | Io | 30 | Helike | 55 | Cyllene | 80 | S/2017 J 2 |
| 6 | Europa | 31 | S/2022 J 1 | 56 | Erinome | 81 | S/2016 J 2 |
| 7 | Ganymede | 32 | Ananke | 57 | Euanthe | 82 | S/2003 J 10 |
| 8 | Callisto | 33 | Praxidike | 58 | Euporie | 83 | Carpo |
| 9 | Themisto | 34 | Iocaste | 59 | Hegemone | 84 | Euporie |
| 10 | Leda | 35 | Hermippe | 60 | Herse | 85 | S/2003 J 23 |
| 11 | S/2018 J 2 | 36 | Thyone | 61 | Isonoe | 86 | S/2017 J 10 |
| 12 | Himalia | 37 | Harpalyke | 62 | Kale | 87 | S/2017 J 11 |
| 13 | Ersa | 38 | Mneme | 63 | Kallichore | 88 | Kallichore |
| 14 | Pandia | 39 | Aoede | 64 | Kalyke | 89 | S/2003 J 4 |
| 15 | S/2011 J 3 | 40 | Cyllene | 65 | Kore | 90 | Kore |
| 16 | Lysithea | 41 | Erinome | 66 | Pasithee | 91 | Eukelade |
| 17 | Elara | 42 | Euanthe | 67 | Sinope | 92 | S/2011 J 1 |
| 18 | Dia | 43 | Euporie | 68 | Sponde | 93 | S/2003 J 5 |
| 19 | S/2018 J 4 | 44 | Hegemone | 69 | S/2003 J 16 | 94 | S/2003 J 8 |
| 20 | Carpo | 45 | Herse | 70 | S/2003 J 19 | 95 | S/2003 J 22 |
| 21 | Valetudo | 46 | Isonoe | 71 | S/2003 J 2 | 96 | S/2003 J 11 |
| 22 | S/2003 J 12 | 47 | Kale | 72 | S/2003 J 15 | 97 | S/2003 J 13 |
| 23 | Euporie | 48 | Kallichore | 73 | S/2003 J 3 | ||
| 24 | S/2003 J 18 | 49 | Kalyke | 74 | S/2003 J 14 | ||
| 25 | S/2010 J 2 | 50 | Kore | 75 | S/2003 J 7 |
Naming of Jupiter’s Moons
The names of Jupiter’s moons come from characters in Greco‑Roman mythology associated with Zeus (the Greek equivalent of the Roman god Jupiter). Most are lovers, descendants, or companions of the god. The names of the four Galilean moons (Io, Europa, Ganymede, and Callisto) date to the 17th century after suggestions by Simon Marius, a contemporary of Galileo.
In modern times, the International Astronomical Union (IAU) oversees the naming process. Newly discovered moons first receive a provisional designation based on the year of discovery (for example, S/2022 J 2). Once follow-up observations confirm the orbit, the discoverers propose a permanent name following IAU conventions:
- Prograde moons (orbiting in the same direction as Jupiter’s rotation) have names ending in ‑a or ‑o.
- Retrograde moons (orbiting in the opposite direction) have names ending in ‑e.
- Names come from mythology and cannot duplicate those of other major Solar System bodies.
Some very small moons remain unnamed for years because their faintness makes follow‑up tracking difficult, delaying official confirmation.
Why the Moon Count Changes
The number of confirmed moons around Jupiter is in constant flux. New discoveries, changes in observational capabilities, and the challenges of tracking faint objects all play a role. Understanding the reasons behind this shifting tally helps explain why “how many moons does Jupiter have” is never a fixed answer.
- New discoveries: Modern wide-field telescopes regularly detect new faint moons, often in distant irregular orbits.
- Provisional designations: New objects are given temporary labels (e.g., S/2023 J 2) until their orbits are confirmed.
- Lost and recovered moons: Some faint moons disappear from view and are later re-identified.
- Temporary captures: Occasionally, objects pass close enough to Jupiter to be briefly captured before escaping.
- Naming process: The IAU names a moon only after its orbit is secure; many small moons remain unnamed.
Origin and Evolution of the Jovian Satellites
The moons of Jupiter formed and evolved through a combination of processes that occurred both during the planet’s birth and over billions of years of Solar System history. Astronomers divide the system into two broad origin types: regular satellites and irregular satellites.
Regular satellites include the Galilean moons and the small inner moons. They likely formed within a disk of gas and dust that surrounded Jupiter after it accreted its mass. This circumjovian disk resembled a miniature version of the Solar System’s protoplanetary disk, with material gradually coalescing into larger bodies. These moons settled into nearly circular, low‑inclination orbits aligned with Jupiter’s equator. Their compositions and densities reflect a gradient in the disk: the innermost moons are rockier due to higher temperatures, while outer large moons retain more water ice.
Irregular satellites describe most of Jupiter’s moons by number. These moons likely are captured objects, such as asteroids or fragments from collisions. Their distant, inclined, and often retrograde orbits point to origins outside the circumjovian disk. Capture likely occurred when small bodies passed close to Jupiter and lost enough energy, possibly through interactions with the planet’s extended gas envelope during its formation or through gravitational encounters with existing moons.
Over time, collisions among moons and with passing comets or asteroids produced the current population. Many small irregular moons are likely fragments from ancient impacts. Some groups, such as the Carme and Pasiphae clusters, share similar orbital parameters and colors, suggesting a single parent body that broke apart.
The Galilean moons have undergone significant internal evolution. Io’s intense volcanic activity is driven by tidal heating from Jupiter’s gravity and orbital resonances with Europa and Ganymede. Europa’s interior heat likely maintains a global subsurface ocean, while Ganymede’s magnetic field points to a differentiated, molten core. Callisto, further out, appears to have evolved more slowly, retaining a heavily cratered surface.
Jupiter’s moon system continues evolving today. Gravitational interactions gradually shift orbits, impacts still occur, and ongoing tidal heating reshapes the interiors of the largest moons. The combination of primordial formation, capture events, and billions of years of dynamical change makes the Jovian satellite system one of the most complex and diverse in the Solar System.
The Galilean Moons: Discovery & Significance
Discovered in January 1610 by Galileo Galilei, the four Galilean moons (Io, Europa, Ganymede, and Callisto) were the first objects found to orbit another planet. This discovery helped overturn the geocentric model of the Solar System.
- Ganymede: Largest moon in the Solar System, larger than Mercury, with its own magnetic field.
- Io: Most volcanically active body in the Solar System.
- Europa: Likely harbors a global subsurface ocean beneath its icy crust.
- Callisto: Ancient, heavily cratered surface, possibly with a subsurface ocean.
These four moons account for almost all the mass of Jupiter’s moon system.
Other Moon Groups
Beyond the Galilean moons, Jupiter’s satellite system includes smaller moons with very different origins and orbits. These groups, classified by their location and orbital direction, include both regular moons that likely formed with the planet and irregular moons that may be captured objects.
- Inner regular moons: Metis, Adrastea, Amalthea, Thebe are small moons that orbit close to Jupiter, contributing dust to its faint rings.
- Prograde irregular moons: Himalia and Elara are examples of moons that orbit in the same direction as Jupiter’s rotation, often far from the planet.
- Retrograde irregular moons: Pasiphae and Carme are examples of moons that orbit in the opposite direction to Jupiter’s rotation, often thought to be captured asteroids.
- Notable odd orbits: Valetudo and Carpo have unusual inclinations or orbits that intersect with other groups.
Jupiter vs. Saturn
In early 2023, Jupiter’s moon count rose to 92, surpassing Saturn’s 83 at the time. By 2025, further discoveries increased Jupiter’s total to 97. Saturn, however, continues to be a strong contender, and future surveys may see the lead shift again. Both planets have many moons due to their strong gravity and ability to capture small objects.
Observing Jupiter’s Moons
While not visible to the unaided eye, you can see the four Galilean moons with binoculars or a small telescope as bright points on either side of Jupiter. Their positions change from night to night. All other moons are too faint for amateur viewing.
Spacecraft Exploration
Spacecraft missions offer close-up views of Jupiter’s moons, revealing details impossible to see from Earth. These missions transform our understanding of their geology, composition, and potential for harboring life.
- Galileo Orbiter (1995–2003): First spacecraft to orbit Jupiter, studied all the major moons.
- Juno (2016–present): Primarily studies Jupiter’s atmosphere and magnetosphere, but also captures occasional images of moons.
- Europa Clipper (launched October 2024): Will conduct detailed flybys of Europa to investigate its ice shell and potential habitability.
- JUICE (Jupiter Icy Moons Explorer, launched 2023): Will arrive in 2031 to study Ganymede, Europa, and Callisto, eventually orbiting Ganymede.
Fun and Interesting Facts
The moons of Jupiter are full of surprises, from giant worlds with magnetic fields to tiny bodies in chaotic orbits. These facts highlight some of the most remarkable and unusual aspects of the Jovian satellite system.
- Ganymede’s magnetic field interacts with Jupiter’s powerful magnetosphere, creating auroras.
- Io’s volcanic plumes can reach 500 km into space.
- Europa’s ocean may contain more water than all of Earth’s oceans combined.
- Many small moons are remnants of collisions between earlier satellites.
- Naming conventions: prograde moons usually end in “a” or “o,” retrograde moons in “e.”
FAQs About Jupiter’s Moons
Q: Is 97 the final number of Jupiter’s moons?
A: No. The number will increase as more moons are discovered and confirmed in coming years.
Q: Which is Jupiter’s largest moon?
A: Ganymede, the largest moon in the Solar System.
Q: Can I see Amalthea from Earth?
A: No. It is too faint; only the Galilean moons are visible to amateurs.
Q: Why do some moons orbit backwards?
A: Retrograde moons are likely captured objects with inclined orbits.
Q: Which mission will study Europa?
A: NASA’s Europa Clipper, set to arrive in the early 2030s.
References
- Alibert, Y.; Mousis, O.; Benz, W. (2005). “Modeling the Jovian subnebula I. Thermodynamic conditions and migration of proto-satellites”. Astronomy & Astrophysics. 439 (3): 1205–13. doi:10.1051/0004-6361:20052841
- Ashton, Edward; Beaudoin, Matthew; Gladman, Brett (2020). “The Population of Kilometer-scale Retrograde Jovian Irregular Moons”. The Planetary Science Journal. 1 (2): 52. doi:10.3847/PSJ/abad95
- Grav, Tommy; Holman, Matthew J.; Gladman, Brett J.; Aksnes, Kaare (2003). “Photometric survey of the irregular satellites”. Icarus. 166 (1): 33–45. doi:10.1016/j.icarus.2003.07.005
- Sagan, Carl (1976). “On Solar System Nomenclature”. Icarus. 27 (4): 575–576. doi:10.1016/0019-1035(76)90175-5
- Schilling, Govert (September 8, 2020). “Study Suggests Jupiter Could Have 600 Moons“. Sky & Telescope.
- Xi, Zezong Z. (1981). “The Discovery of Jupiter’s Satellite Made by Gan De 2000 years Before Galileo“. Acta Astrophysica Sinica. 1 (2): 87.