19 Largest Moons in the Solar System

The solar system is home to a wide variety of moons, each with its own unique characteristics and features. Some of these natural satellites are larger than entire planets, while others are marked by active volcanoes, icy oceans, or ancient craters. These moons provide valuable insights into the history and evolution of their parent planets and the solar system itself. From the massive Ganymede orbiting Jupiter to Neptune’s icy Triton, each of these moons tells a fascinating story about the forces shaping their environments. Let’s explore the 19 largest moons in the solar system and discover what makes each one special.

Ganymede (Jupiter)

Ganymede is the largest moon in the solar system, with a massive diameter of 5,268 kilometers. It even surpasses Mercury in size, though it lacks the planetary status due to its orbit around Jupiter. Ganymede’s surface features a mix of heavily cratered regions and smoother areas with long grooves, suggesting past tectonic activity. Unlike other moons, Ganymede possesses its own magnetic field, a characteristic usually associated with planets. Below its icy surface, scientists suspect there is a salty ocean, potentially holding more water than all of Earth’s oceans combined. Its size, magnetic field, and potential for an underground ocean make it a captivating subject for future exploration.

Titan (Saturn)

Titan, Saturn’s largest moon, spans 5,151 kilometers in diameter, making it the second-largest moon in the solar system. What sets Titan apart is its dense, nitrogen-rich atmosphere, thicker than Earth’s, with surface pressure 1.5 times that of our planet. Methane and ethane rain from its skies, forming lakes and rivers, giving Titan a strangely Earth-like appearance. Its surface is shrouded in an orange haze, making direct observation difficult, but radar mapping has revealed dunes, mountains, and seas of liquid hydrocarbons. Beneath its thick ice crust, scientists theorize there may be a water ocean, possibly harboring life. Titan’s unique atmosphere and surface make it one of the most intriguing celestial bodies for future missions.

Callisto (Jupiter)

Callisto, Jupiter’s second-largest moon, has a diameter of 4,821 kilometers, making it the third-largest moon in the solar system. It is the most heavily cratered object in the solar system, with its ancient surface showing little sign of geological activity. Unlike its neighboring moons, Callisto has no signs of tectonic activity, but its lack of internal heating has preserved its primordial features. Despite its frozen, cratered surface, Callisto might have a subsurface ocean beneath its icy shell. This potential ocean makes it a candidate for harboring simple life forms, although its deep freeze may limit this possibility. Callisto’s unchanging surface offers a glimpse into the early solar system’s history.

Io (Jupiter)

Io, Jupiter’s third-largest moon at 3,643 kilometers in diameter, is the most volcanically active body in the solar system. Its surface is covered with sulfur in various colorful forms, giving it a unique, alien appearance. Unlike Earth’s volcanoes, Io’s are driven by tidal heating caused by gravitational interactions with Jupiter and other nearby moons. This intense volcanic activity constantly reshapes Io’s surface, covering it with lakes of lava and plumes of volcanic gases. Despite its fiery appearance, Io has an icy core, with frozen sulfur dioxide snowfields blanketing parts of the landscape. Its extreme volcanism and dynamic surface make it an exciting target for scientists studying planetary geology.

Moon (Earth)

Earth’s moon, with a diameter of 3,474 kilometers, is the fifth-largest in the solar system and the largest relative to its parent planet. It is the only natural satellite humans have set foot on, making it a key player in space exploration history. The moon’s surface is covered with craters, plains of hardened lava, and large maria, or “seas,” formed by ancient volcanic activity. Its gravitational pull creates ocean tides on Earth, and it’s slowly moving away from us at about 3.8 centimeters per year. The moon also has a small, iron-rich core, though it lacks a significant atmosphere. Its influence on Earth’s tides and its role in eclipses make it one of the most studied celestial bodies.

Europa (Jupiter)

Europa, the fourth-largest moon of Jupiter, has a diameter of 3,121 kilometers, making it the smallest of the Galilean moons. Its smooth, icy surface, crisscrossed by dark streaks, suggests it may have a subsurface ocean beneath its frozen crust. Europa’s ice-covered world likely holds more water than all of Earth’s oceans combined. The moon’s internal heating, caused by tidal forces from Jupiter, could create warm, liquid water environments beneath the surface, raising the possibility of life. Europa’s potential for harboring life has made it a high-priority target for future space missions. Its combination of ice and possible oceans below has captured the imagination of scientists and space enthusiasts alike.

Triton (Neptune)

Triton, Neptune’s largest moon, has a diameter of 2,706 kilometers and is the only large moon in the solar system with a retrograde orbit, meaning it orbits in the opposite direction of its planet’s rotation. This suggests that Triton may have been captured by Neptune’s gravity, possibly from the Kuiper Belt. Its surface is a frozen nitrogen landscape, dotted with geysers that spew nitrogen gas into space. Despite its icy exterior, Triton may have a warm, active interior, hinting at a subsurface ocean. The moon’s thin atmosphere, primarily nitrogen, gives it a delicate blue sheen. Triton’s unusual orbit and surface activity make it a mystery waiting to be explored.

Titania (Uranus)

Titania, the largest moon of Uranus, measures 1,578 kilometers in diameter. Its icy surface is marked by deep valleys and fault lines, suggesting tectonic activity in its past. Titania is thought to have a rocky core surrounded by an icy mantle, with the possibility of a subsurface ocean. The moon’s surface is relatively dark, reflecting only about 35% of the sunlight it receives. Its sparse, thin atmosphere is composed mainly of carbon dioxide, with traces of methane. The complex geology of Titania hints at an active history, even though the moon is now mostly dormant.

Rhea (Saturn)

Rhea, Saturn’s second-largest moon, has a diameter of 1,527 kilometers. Its surface is covered in bright, icy plains and is heavily cratered, much like Earth’s moon. Rhea’s composition is mostly water ice, but it likely has a small rocky core. One of Rhea’s most intriguing features is the possibility of a thin ring system, although this remains unconfirmed. It has a tenuous atmosphere composed of oxygen and carbon dioxide, possibly generated by chemical reactions on its surface. Rhea’s simple, frozen landscape provides insight into the ancient conditions of the outer solar system.

Oberon (Uranus)

Oberon, Uranus’s second-largest moon, has a diameter of 1,522 kilometers and is the farthest from the planet among its large moons. Its surface is heavily cratered and covered in ancient ice, with some of the craters showing evidence of dark material that could be upturned during impacts. Like Titania, Oberon is thought to have a rocky core and an icy mantle, with the potential for a subsurface ocean. The moon’s dark surface reflects little sunlight, making it difficult to observe in detail. Oberon’s distant orbit and heavily cratered surface give it a haunting, frozen appearance, largely unchanged over billions of years.

Iapetus (Saturn)

Iapetus, one of Saturn’s more peculiar moons, has a diameter of 1,471 kilometers and is known for its starkly contrasting hemispheres. One side of the moon is as dark as coal, while the other is bright and reflective. This unusual dichotomy has puzzled scientists for years, but it may be due to material being deposited from another nearby moon, Phoebe. Iapetus also has an equatorial ridge that gives it a distinctive walnut shape, with some peaks reaching up to 20 kilometers in height. Its slow rotation causes it to take 79 days to complete one orbit around Saturn. Iapetus’s contrasting surface and unique shape make it one of the most visually striking moons in the solar system.

Dione (Saturn)

Dione, Saturn’s fourth-largest moon, has a diameter of 1,123 kilometers and is composed mostly of water ice, with a rocky core. Its surface is marked by bright, icy cliffs and deep valleys, indicating past tectonic activity. The moon’s heavily cratered landscape suggests that it has been geologically inactive for billions of years, though some regions appear younger than others. Like Rhea, Dione may have a thin atmosphere, although it’s mostly composed of oxygen ions. The Cassini mission discovered that Dione might have a subsurface ocean, adding it to the list of moons with potential for harboring life. Dione’s icy surface and internal ocean make it an interesting target for future exploration.

Tethys (Saturn)

Tethys, another of Saturn’s moons, has a diameter of 1,060 kilometers and is composed primarily of water ice. Its surface is dominated by one of the largest impact craters in the solar system, Odysseus, which stretches across nearly half the moon. Tethys also has a massive valley system, Ithaca Chasma, which may have formed as the moon’s interior cooled and expanded. The moon’s icy surface is highly reflective, bouncing back much of the sunlight that hits it. Tethys is believed to have a cold, inactive interior, although past geological activity is evident from its surface features. The combination of large craters and massive valleys makes Tethys a fascinating moon to study.

Enceladus (Saturn)

Enceladus, Saturn’s sixth-largest moon, has a diameter of only 504 kilometers, but it has captured significant attention due to its active geysers that spew water vapor and ice particles into space. These geysers are powered by tidal forces from Saturn, which keep Enceladus’s interior warm enough for liquid water to exist beneath its icy crust. The moon’s surface is one of the brightest in the solar system, reflecting almost all of the sunlight that strikes it. The Cassini mission discovered that Enceladus has a global subsurface ocean, increasing its potential to support life. The geysers create a huge plume of material that feeds one of Saturn’s rings. Enceladus’s active geology and potential for life make it a top priority for future missions.