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100 Fascinating Facts About Ganymede, Jupiter’s Largest Moon

A stunning view of Ganymede, Jupiter’s largest moon, revealing its icy surface and cratered terrain as captured by NASA’s Galileo spacecraft. Image Credit: NASA

Updated on May 02, 2025 | By Jameswebb Discovery Editorial Team

Ganymede, the largest moon in our solar system, is a celestial marvel orbiting Jupiter. Discovered by Galileo Galilei in 1610, this icy giant is bigger than Mercury and even rivals planets in its complexity. From its unique magnetic field to its potential subsurface ocean, Ganymede captivates astronomers and space enthusiasts alike. In this comprehensive guide, we unveil 100 fascinating facts about Ganymede, exploring its physical characteristics, scientific significance, and role in future space exploration. Whether you’re a student, an amateur astronomer, or simply curious about the cosmos, these facts will deepen your appreciation for this extraordinary moon.

Table of Contents

What is Ganymede?
Physical Characteristics
Scientific Discoveries
Ganymede’s Role in Space Exploration
Fun and Cultural Facts
FAQs About Ganymede

What is Ganymede?

Largest Moon in the Solar System: Ganymede is the biggest moon, with a diameter of 5,268 km (3,273 miles), larger than Mercury and Pluto.
Orbits Jupiter: It is one of Jupiter’s 95 known moons, specifically one of the four Galilean moons.
Discovery by Galileo: Galileo Galilei first observed Ganymede on January 7, 1610, using a rudimentary telescope.
Named After Mythology: Ganymede is named after a Trojan prince in Greek mythology, abducted by Zeus to serve as a cupbearer.
Seventh Moon from Jupiter: It orbits at an average distance of 1.07 million km (665,000 miles) from Jupiter.
Why It Matters: Ganymede’s size and unique features make it a prime target for studying planetary formation and habitability.

Physical Characteristics

Bigger Than Mercury: Ganymede’s diameter is 8% larger than Mercury’s (4,879 km).
Icy Surface: Its surface is primarily water ice, with some rocky material.
Two Types of Terrain: Ganymede has dark, heavily cratered regions and lighter, grooved terrains.
Cratered Dark Regions: These older areas, like Galileo Regio, date back billions of years.
Grooved Terrains: Younger, tectonically active regions feature ridges and grooves, suggesting past geological activity.
Low Density: Its density of 1.94 g/cm³ indicates a mix of ice and rock.
Thin Atmosphere: Ganymede has a tenuous oxygen atmosphere, detected by the Hubble Space Telescope.
Surface Temperature: Temperatures range from -112°C to -183°C (-170°F to -297°F).
Albedo of 0.43: Its icy surface reflects 43% of incoming sunlight, making it relatively bright.
Impact Craters: Large craters like Tros and Cisti are evidence of ancient meteorite impacts.
Bright Ray Craters: Younger craters, like Osiris, have bright ejecta rays from recent impacts.
Polar Caps: Frosty polar caps, likely water ice, cover its poles.
Tectonic Features: Grooves and ridges suggest past stretching and cracking of the crust.
No Volcanic Activity: Unlike Io, Ganymede shows no signs of current volcanism.
Magnetic Field: Ganymede is the only moon known to have its own magnetic field.

Pro Tip: Use a telescope with at least 100x magnification to spot Ganymede as a faint dot near Jupiter. Check our guide to telescopes for recommendations.

Scientific Discoveries

Subsurface Ocean: Evidence from NASA’s Galileo spacecraft suggests a saltwater ocean beneath the ice.
Ocean Depth: This ocean may be 100–150 km deep, containing more water than Earth’s oceans.
Magnetic Field Origin: Its magnetic field is likely generated by a molten iron or iron-sulfide core.
Interaction with Jupiter: Ganymede’s magnetic field interacts with Jupiter’s, creating auroras.
Auroral Evidence: Hubble observations in 2015 confirmed auroras, supporting the ocean hypothesis.
First Detailed Images: NASA’s Voyager 1 and 2 (1979) provided the first close-up images.
Galileo Mission: The Galileo spacecraft (1995–2003) mapped 99% of Ganymede’s surface.
James Webb Space Telescope (JWST): JWST is studying Ganymede’s composition in 2025, revealing new details.
Salty Ocean: Magnetic data suggests the ocean contains salts, increasing its conductivity.
Geological Activity: Past tectonic activity likely reshaped the surface 2–3 billion years ago.
Core Structure: Ganymede has a layered interior: a metallic core, rocky mantle, and icy crust.
Oxygen in Atmosphere: Trace oxygen is likely produced by solar radiation splitting water ice.
No Carbon Dioxide: Unlike Callisto, Ganymede’s atmosphere lacks significant CO₂.
Surface Age: Dark regions are ~4 billion years old, while grooved terrains are younger.
Impact History: Craters indicate a violent early history during the Late Heavy Bombardment.
Tidal Heating: Tidal forces from Jupiter may have driven past geological activity.
No Rings: Unlike Saturn’s moons, Ganymede has no ring system.
Low Radiation: Its distance from Jupiter reduces radiation exposure compared to Io or Europa.
Potential for Life: The subsurface ocean raises questions about habitability, though conditions are harsh.
Comparison to Europa: Ganymede’s ocean is deeper but less likely to interact with the rocky core.

Learn More: Explore how JWST is revolutionizing our understanding of moons in our James Webb facts article.

Ganymede’s Role in Space Exploration

JUICE Mission: ESA’s Jupiter Icy Moons Explorer (JUICE), launched in 2023, will study Ganymede in 2034.
First Orbital Target: JUICE will be the first spacecraft to orbit Ganymede, starting in 2034.
Scientific Goals: JUICE aims to map the surface, study the ocean, and analyze the magnetic field.
Voyager Flybys: Voyager 1 and 2 flew by in 1979, capturing initial data.
Galileo Flybys: The Galileo spacecraft made six close flybys between 1996 and 2000.
Juno Mission: NASA’s Juno, orbiting Jupiter since 2016, indirectly studies Ganymede’s environment.
Future Landers: Proposed missions aim to land on Ganymede to sample its ice.
Astrobiology Interest: Ganymede is a secondary target for astrobiology after Europa.
Magnetic Field Studies: Its unique magnetic field makes it a key target for planetary science.
Technological Challenges: Radiation and distance pose challenges for Ganymede missions.
International Collaboration: JUICE involves ESA, NASA, and JAXA contributions.
Orbital Period: Ganymede takes 7.15 Earth days to orbit Jupiter.
Resonance with Other Moons: It’s in a 1:2:4 orbital resonance with Europa and Io.
Exploration Timeline: Data from JUICE will transform our understanding by 2035.
Cost of JUICE: The mission costs approximately €1.5 billion.
Launch Details: JUICE launched on an Ariane 5 rocket from French Guiana.
Travel Time: It will take 8 years to reach Jupiter, arriving in 2031.
Power Source: JUICE uses solar panels, despite Jupiter’s distance from the Sun.
Instrument Suite: JUICE carries 10 instruments, including cameras and spectrometers.
Ganymede’s Priority: Ganymede was chosen for its ocean and magnetic field.

Stay Updated: Follow the latest mission updates in our astronomy news section.

Fun and Cultural Facts

Sci-Fi Inspiration: Ganymede appears in novels like 2001: A Space Odyssey by Arthur C. Clarke.
Video Game Presence: It’s featured in games like Mass Effect and Dead Space.
Popular in Art: Artists depict Ganymede’s icy surface in cosmic illustrations.
Astronomy Clubs: Ganymede is a favorite for amateur astronomers observing Jupiter.
Visible with Binoculars: On clear nights, Ganymede can be seen with 10x50 binoculars.
Cultural Symbol: Its mythological name ties to themes of beauty and service.
Star Wars Connection: Ganymede’s icy terrain inspires fictional icy planets like Hoth.
Educational Tool: It’s often used in classrooms to teach about moons and orbits.
Astrophotography Target: Ganymede is a challenging but rewarding subject for astrophotographers.
Public Interest: Google Trends shows rising searches for “Ganymede facts” in 2025.
Space Tourism Potential: Future missions could make Ganymede a tourist destination.
Named Features: Regions like Galileo Regio honor famous astronomers.
Crater Names: Craters are named after mythological figures, like Anubis and Osiris.
No Human Footprints: Ganymede remains untouched by human exploration.
In Pop Culture: TV shows like The Expanse reference Ganymede as a colony.
Astronomy Apps: Apps like Stellarium help locate Ganymede in the sky.
Public Events: Planetariums often highlight Ganymede during Jupiter observation nights.
Merchandise: Ganymede-themed posters and models are popular among enthusiasts.
Social Media Buzz: X posts about Ganymede trend during JUICE mission updates.
Educational Videos: YouTube channels like NASA feature Ganymede animations.

Get Involved: Try astrophotography with tips from our astrophotography guide.

Additional Facts About Ganymede

Mass: Ganymede is 1.48 × 10²³ kg, twice the Moon’s mass.
Gravity: Its surface gravity is 1.43 m/s², about 1/6th of Earth’s.
Escape Velocity: You’d need 2.74 km/s to escape Ganymede’s gravity.
No Tides: Unlike Earth, Ganymede has no significant tidal effects on its surface.
Orbital Inclination: Its orbit is tilted 0.2° relative to Jupiter’s equator.
Eccentricity: The orbit is slightly elliptical, with an eccentricity of 0.0013.
Synchronic Rotation: Ganymede is tidally locked, always showing one face to Jupiter.
Surface Pressure: The atmosphere’s pressure is less than 1 micropascal.
No Weather: The thin atmosphere lacks weather systems.
Radiation Belts: Ganymede’s magnetic field creates mini-radiation belts.
Comparison to Titan: Both have atmospheres, but Ganymede’s is thinner.
No Rings Around Jupiter: Ganymede doesn’t contribute to a ring system.
Color: Its surface appears grayish with reddish-brown patches.
Dust Particles: Micrometeorite impacts create a thin dust layer on the surface.
No Active Geysers: Unlike Enceladus, Ganymede has no observed geysers.
Historical Observations: Early telescopes mistook Ganymede for a star.
Modern Imaging: JWST’s infrared capabilities reveal new surface details.
Citizen Science: Projects like JunoCam involve the public in Ganymede studies.
Future Discoveries: JUICE may confirm the ocean’s depth and composition.
Legacy: Ganymede’s study advances our understanding of icy worlds and habitability.

FAQs About Ganymede

Q: What is Ganymede known for?
A: Ganymede is known for being the largest moon in the solar system, its subsurface ocean, and its unique magnetic field.

Q: Can you see Ganymede from Earth?
A: Yes, with binoculars or a small telescope, Ganymede appears as a bright dot near Jupiter.

Q: Does Ganymede have life?
A: While its ocean raises possibilities, there’s no evidence of life due to harsh conditions.

Q: How far is Ganymede from Earth?
A: The distance varies, averaging 628 million km (390 million miles) due to orbital paths.

Q: Why is Ganymede important for space exploration?
A: Its ocean and magnetic field make it a key target for studying habitability and planetary science.

Conclusion

Ganymede is more than just Jupiter’s largest moon—it’s a window into the complexities of icy worlds and the potential for life beyond Earth. From its subsurface ocean to its magnetic field, these 100 fascinating facts highlight why Ganymede is a cornerstone of planetary science. Stay tuned for updates from the JUICE mission and explore more cosmic wonders on James Webb Discovery.

Sources: NASA, ESA, Hubble Space Telescope, Galileo Mission, JUICE Mission documentation.