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Other Moons
Quick Facts
 
Largest Moon: Ganymede
 
Smallest Moons: S/2003 J9 and S/2003 J12
 
Most Moons: Jupiter
 
Least Moons: Mercury, Venus, Ceres
 
First Discovered: Europa, Io, Callisto, Ganymede
 
Recently Discovered: S/2007 S1, S2, S3
 

Other Moons

Although the Earth's Moon is most well known of all moons, there are many others worth studying. Some planets have many moons, while others have none at all. Even dwarf planets Pluto and Eris have moons!

Irregular moons are moons that have an unknown origin. They might be captured asteroids or comets, or just pieces of a once larger object. Regular moons are the ones we are most familiar with, such as the moons of Uranus or Pluto. These moons are often formed by collision and impact.

Image at right: Europa, Ganymede, Io, Callisto (Original image courtesy of NASA. Edits by A. Rickhoff, Adler Planetarium).

DID YOU KNOW?
Galileo was the first to spot Jupiter's moons.
Saturn's small moon, Epimetheus (Courtesy of NASA)
Saturn's small moon, Epimetheus (Courtesy of NASA)
Features

Scientists have to come up with a definition for a moon except that it is an object that orbits or goes around another object. Since many objects fit this broad definition, moons have a wide variety of features. Some moons are rock that has been captured by the planet's gravity. Other moons like Europa and Titan have atmospheres and are thought to house liquid water, and possibly life.

Irregular moons are usually very small and very far from the planet they orbit. Often they will orbit the opposite way that other moons do. Irregular moons are usually older than regular moons. Regular moons are usually large round moons that orbit their planet in a mostly circular shape, as our Moon does.

Learn more about types of moons at Space.com

Voyager Spacecraft (Courtesy of NASA)
Voyager Spacecraft (Courtesy of NASA)
Missions

Looking at other moons began in 1609 when Galileo Galilei pointed a telescope to the heavens and discovered Jupiter's moons. He originally named them after his wealthy and powerful patrons, the Medici family, but which we now call the Galilean moons in his honor.

Over the course of many hours, Galileo was able to observe the four largest moons: Io, Europa, Callisto, and Ganymede, orbiting around Jupiter. This observation reinforced the ideas of Copernicus which say that, except for the Moon, the objects in the heavens do NOT orbit around the Earth. In 2009, we join the United Nations and the International Astronomical Union in celebrating this discovery during the International Year of Astronomy.

Since Galileo's discovery, NASA has sent other missions out to explore other moons. The Voyager mission photographed the moons of Jupiter and Saturn while Mariner 9 captured Mars' moons Phobos and Deimos while observing the red planet. Currently the Cassini-Huygens mission is exploring the mysteries of Saturn's many moons and rings.

Learn more about IYA 2009 at the Astronomy 2008 website.

Pan Greek god of shepherds and flocks (2003, Florida Center for Instructional Technology)
Pan Greek god of shepherds and flocks (2003, Florida Center for Instructional Technology)
Myths, Stories, and More

Did you ever wonder how planet moons got their names? Many come from ancient myths, such as Saturn's moons, Atlas and Pan. In Roman mythology, Atlas was punished for fighting against Jupiter and was forced to hold the world on his shoulders. In Greek mythology, Pan was half man, half goat. He was God of woods and fields.

Today, references to the planets' moons show up everywhere from TV shows to video games. You can find references to Jupiter's Moons in TV shows, including Cowboy Bebop, Power Rangers, and Star Trek, and video games, such as Halo 2, Zone of the Enders, and Final Fantasy VI.

Read a near complete list of Jupiter's Moons in fiction on wikipedia

Jupiter's Moon Europa (Courtesy of NASA)
Saturn's Moon Titan (NASA, Cassini-Huygens)
Earth Matters

We have our own moon, why do we care so much about other moons? While many moons are rocky wastelands, liquid water may exist on others, and moons like Europa and Titan may even harbor the possibility of life.

Saturn's moon Titan is the only moon to have a dense atmosphere and the only object with clear evidence of surface liquids other than Earth. Even the features of Titan are similar to Earth, including dunes and shorelines. This means that Titan could possibly have much to tell us about what early Earth looked like and how it formed.

Learn more about Titan on NASA's website.