The shepherd satellites they are small moons that, because of their gravitational influence, keep the material of the rings grouped on giant planets.
The Saturn's rings They are the best known, large and visible. They extend about 200,000 kilometers around the planet, but they are very flat, barely tens of meters thick.
The other giant gaseous planets of the Solar System also have rings, although much less spectacular than those of Saturn and practically invisible even with most telescopes.
For these rings to remain stable, there are some satellites that shepherd. These moons orbit inside or at the edges of ring systems and contribute to their well-defined limits. As? Thanks to gravity, some materials that pass near the shepherd satellite are sent back over the ring; others are expelled to the outside or end up falling on the shepherd satellite itself.
Saturn, which has the most spectacular rings in the Solar System, has several shepherd satellites. Prometheus and Pandora they confine the F ring in a thin strip of material. Pandora is the outer satellite and Prometheus, somewhat larger, the inner satellite. Pampering It is responsible for the existence of the largest gap between rings, the Cassini division. Other satellite Saturn shepherds are Atlas, pastor of ring A; Daphne, head of the Keeler Division, and Bread, responsible for the Encke Division.
Jupiter it also has rings and pastoral moons, like Metis and Adrastea, who shepherd one of their inner rings of Jupiter. Being both inside the Roche boundary of the planet it is possible that the ring material comes from the satellites themselves since they are in conditions close to the rupture due to the effects of Jupiter's tide.
Shepherd satellites are known on other planets with rings. So, the planet Uranus has the moons Cordelia and Ophelia that act as inner and outer shepherdesses of their epsilon ring. For its part, the planet Neptune It has at least one pastor satellite, Galatea, responsible for keeping Adams ring in place.
How the shepherd satellite system works
The gravity of the shepherd satellite accelerates the particles of the outer ring and slows down those of the inner one, thereby opening a gap whose width depends on the mass of the satellite.
Following the laws of physics, an inner particle moves faster than an outer one. As a consequence, the satellite (which is in the middle) advances to the exteriors and is advanced by the interiors. When passing nearby, its gravitational influence attracts these materials, so that it slows down those who pass through the interior (closer to the planet) and accelerates those who pass through it.
The force that the satellite exerts on each inner particle is opposed to the direction of its orbital motion; therefore, by slowing it down, it causes it to fall into a lower orbit. That same force acts backwards on the outer particles, that is, it pushes them in the same direction of their orbital movement; This moves them to a higher orbit. In this way, the shepherd satellite cleans materials the way to either side of its path and keeps the rings in order and, in passing, its own orbit cleared.
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