Solar System Moons

the moon
Our own grey and inactive moon
There are over 170 known moons in our solar system, many of which are just as or even more remarkable than the planets. When we first began to explore the solar system we expected to find rather bland, colorless, inactive moons like our own, we couldn’t have been more wrong.

What we found were geologically active worlds undergoing constant violent eruptions, bodies with underground oceans which may contain alien life forms, moons that were larger than the planet Mercury, and an intriguing moon orbiting the planet Saturn with a thick atmosphere and lakes of liquid on its surface. Below are some of the most amazing moons of our solar system.


moon io
This is the dazzling Jupiter moon Io, it is the first of the Galilean moons, named after the Italian astronomer Galileo Galilei after his discovery in 1610. The first thing you’ll notice is how colorful it is, this is due to Io being volcanically active. Sulphur dioxide is deposited all over the moon due to its constant volcanic eruptions making it look rather like a pizza.

At first scientists couldn’t figure out how an object in such a cold area of the solar system could be generating so much heat. The answer lay with its very large host, Jupiter. The planet exhorts huge gravitational forces upon the moon, pushing and pulling it causing friction underneath its surface, which in turn creates molten lava, making Io the most volcanically active body in the entire solar system.


The icy moon Europa is the second of the Galilean moons. It orbits Jupiter at an average distance of around 417,000 miles and is a little smaller than our own moon. Its surface is covered with thick ice, but what’s more interesting is what lies beneath. Europa is under similar gravitational forces that are exerted on Io, but instead of creating lava the ice underneath its surface is turned into water. It is estimated that Europa possesses more liquid water than Earth!

Where there is water there could be life, there is the intriguing possibility that alien life, probably in microbial form, exists in the warm water of Europa. Who knows, there may even possibly be primitive animals swimming around its underground oceans. Finding out will be difficult but if we do it may answer the eternal question “are we alone in the universe?”


This is Ganymede, the third of the Galilean moons. It orbits Jupiter at an average distance of around 665,000 miles which is just over 1 million kilometers. It is worthy of note because it is the largest moon in the solar system. It has a diameter of 3,270 miles making it larger than the planet Mercury.

Ganymede also creates its own magnetic field, the only moon in the solar system known to do so. It is thought that magnetic fields such as the one we have around Earth are generated by having an active core.


This is the tiny ice moon Enceladus, it is only 311 miles in diameter and orbits the planet Saturn at an average distance of 148,000 miles. Saturn exerts the same gravitational forces on its moons as Jupiter does, making Enceladus geologically active.

This small moon is cryovolcanic, meaning that instead of erupting with molten lava it spews ice from its fissures. These small ice particles from Enceladus actually make up Saturn’s faint outer ring.


titan moon
Titan is perhaps the most intriguing moon of them all. Like Ganymede it is larger then the planet Mercury making it the second largest moon in the solar system. What is more astonishing about Titan is that it has a thick atmosphere, and like the atmosphere of Earth it is mostly composed of nitrogen.

Before 2004 little was known about Titan, that all changed with the arrival of NASA’s Cassini-Huygens spacecraft. Not only was Cassini able to see past Titan’s thick clouds it also launched the Huygens probe which successfully landed onto its surface. The images they sent back to Earth revealed what many would describe as a frozen primordial version of Earth. Titan not only has mountains and valleys but is the only body in the solar system apart from Earth to have liquid on its surface, not liquid water but liquid methane. On Earth methane is primarily a gas but on Titan temperatures are so cold it is turned into a liquid.


triton moon
Lastly we have the Neptune moon Triton, a whopping 2.8 billion miles from the sun. As the Voyager 2 spacecraft passed Triton on its way out of the solar system scientists at Nasa didn’t expect this moon to be active, but it is. Like Enceladus Triton is cryovolcanic, with nitrogen ice crystals erupting from its surface.

Triton has a retrograde orbit, meaning it orbits Neptune in the opposite direction in which the planet rotates, it is the only large moon in the solar system to do so. It is believed that Triton originates from the Kuiper Belt, an area of the solar system beyond Neptune populated by icy bodies, but was somehow captured by the planet’s gravity.

How Big is the Solar System? Examples from which we can measure the size of the solar system.
Galileo Mission Summary of NASA's mission to Jupiter.
Order of Planets The order in which the planets and other bodies of our solar system orbit the sun.
Cassini Mission Summary of NASA's mission to Saturn.
Voyager 1 and 2 Summary of NASA's arguably greatest mission.
Nicolaus Copernicus Biography of the 15th century pioneering astronomer.

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