What is a Shepherd Moon and what does it do

The words “shepherd moon” may bring to mind flocks grazing along green meadows in the moonlight night; however, when applied to celestial bodies, the term brings about another image.  Our solar system is home to many phenomenal objects, but the most beautiful and intriguing include the rings of Saturn, Uranus, Jupiter, and Neptune.  While some may think that these adornments are merely space dust and rock, they would be surprised to learn that the uniqueness of Saturn’s rings is made possible by celestial guardians called shepherd moons.

What is a Shepherd Moon?

Generally, a moon or satellite orbits around its planetary neighbor and affects objects on or around the planet. From the influence of gravity and mass, a moon can affect tides, weather and even the paths of orbiting objects.

The ringed gas giant Saturn has over sixty moons orbiting around it. Neptune, Jupiter, and Uranus have a respectable number as well. Some of the moons circle independent of each planet’s rings; however, many do not.  These satellites, called shepherd moons, orbit within or between the planet’s dust rings.

What Do Shepherd Moon’s Do?

Shepherd moons, also called guardian moons or shepherd satellites, are natural bodies which orbit a planet and through their gravitational affects alter or control the orbits of other objects.  The gravity of each shepherd move serves to create a defining line for the dust ring.  Serving as fences or deflection, the shepherd satellites maintain the clear distinction of orbiting rings.

Shepherd Moons of Saturn

Due to the images from the Hubble Telescope and various deep space probes, discoveries about the outer most planets have increased.  Saturn, known for its beautiful rings, has more than sixty moons.  Of these rings, Pandora and Prometheus appear to be shaping the planet’s F ring system. Also, several other shepherd moons within the Jewel’s large A and B rings help control its numerous individual rings.

Shepherd Moons of Uranus, Neptune and Jupiter 

The discovery of rings around Uranus took place in 1977.  In 2005, the Hubble Telescope helped scientists confirm the major ring system around the planet.  And, like Saturn, Uranus’ rings are kept in check by shepherd satellites.  Cordelia and Ophelia are the most commonly known shepherd moons of the “Bull’s Eye” Planet. It is believed that in addition to these two shepherd moons there are several others that maintain Uranus’ intricate dust ring system.

In 1989, the Voyager 2 spacecraft revealed the four rings of Neptune. Satellites Despina and Galatea serve as shepherd moons for the planet’s Le Verrier and Adams’ rings respectively.

Few knew that the largest planet in our solar system also had a ring system.  Saturn’s only rival for number of satellites; Jupiter’s rings are not as spectacular as Saturn’s.  Jupiter also has its own set of guardian satellites, Amalthea, Metis, Thebe and Adrastea.

Our solar system is an incredibly complete and beautiful place.  Each planet has its own distinct characters which make them unique amongst a family of planets, moons and stars.  The rings girding the giant planets are both a mix of gravitation and wonder. While we may know how they came to be, we know that they are made possible by shepherd moons.

For more information about the solar system or shepherd moons, check out the following websites: