Rings of Saturn

The mission Cassini-Huygens

The rings of Saturn are one of beautiful and of the most surprising spectacles of the solar system.
That is why on July 1st, 2004, the spaceship Cassini-Huygens reduced its speed to be captured by the gravity of Saturn to enter in orbit with this one.
The spaceship will investigate until 2008 the planet, its mysterious moons, its stunning rings and its magnetic environment gives a complex.
Cassini has to make 74 rotations around the planet, get closer to Titan and the other icy moons of Saturn.
The most beautiful of the spectacles is the one all the same that propose us the rings of Saturn, each on his orbit, all aligned in a fine band of some kilometers...

Image: The mission Cassini-Huygens is a cooperative project between the NASA, the European Space agency and the Italian Space agency.
JPL, is the division of the Technological Institute of California to Pasadena, who manages the mission Cassini-Huygens for the Direction of the NASA, in Washington.
The space shuttle Cassini was conceived, developed and assembled by JPL.

The origin of rings

The rings of Saturn are constituted by uncountable particles, each on an appropriate orbit, of silicates, oxide of iron and particles of ice of a size varying of the speck of dust in some meters. Rings extend over a fine layer of more than 400 000 km.
With the exception of the most external ring, they do not exceed 1 km in thickness. All this matter combined in a single object, would be equivalent to the size of Epimetheus Epimetheus Placed on the same orbit as Janus, measures only 138x110x110 km. The shape of this satellite is very irregular and its surface presents big valleys. We can perceive several craters there furthermore of 30 kilometers wide.  or of Prometheus Prometheus is an irregular satellite of Saturn of a size of 148×100×68 km. It presents numerous valleys and cliffs as well as several craters of about twenty kilometers in diameter. It seems less craterised than the nearby moons, Pandore, Janus and Epimetheus. Its weak density and its high albedo seem to indicate that Prometheus is a very porous celestial body of ice. The observations of the 1995s and 1996 put in evidence that Prometheus was late of 20 ° with regard to its position of 1981. This distance cannot explain by errors of observations. It is thus possible that the orbit of Prometheus changed following a collision or that it possesses the moon partner who shares her orbit.  that is no bigger than the moon from 100 to 150 km in diameter.
The theory proposed by Édouard Albert Roche in the 19th century, explains that rings result from the moon of Saturn the orbit of which would have too much got closer to the planet and which would have been broken by the strengths of tide either split by the impact of a comet or an asteroid.
The rings of Saturn are too unstable to last, they thus have a recent origin in the astronomical scale. Since the Earth we can observe three rings, rings (In and B) and a ring more thin.

The zone enters A and B is known under the name of division of Cassini. The ring A is divided by a less visible space named division of Encke.
Voyager probes detected four other much less visible rings.
The ring F, one of the most external, has an extremely complex structure of several interlaced smaller rings. The origin of these knots is unknown but is probably gravitational.
The ring E, the most external, extends over 300 000 km and widens gradually after the orbit of Enceladus until reach 60000 km in thickness. Noted: the equatorial diameter of Saturn is 120536 km.

A complex system

The rings of Saturn maintain complex echo with some of its satellites. Some, named 'satellite shepherds' (Atlas, Prometheus and Pandora), is clearly indispensable for the stability of rings. Mimed seems responsible for the division of Cassini, Piece is situated inside the division of Encke.
The global system is of a very big complexity as shows it the results of the probe Cassini, entered the orbit of Saturn in 2004.
This complex and surprising planetary system intrigues the scientists.
One of these intrigues concerns the division Cassini, that is the big interval situated between rings A and B. While the rings of Saturn almost exclusively consist of water in the form of ice, the data show that the division of Cassini contains more dusts than ice.
The division Cassini discovered to 17th century by Giovanni Domenico Cassini, revealed that the rings of Saturn did not constitute adjoining elements.
Particles situated between rings A and B look like outstandingly what was observed on Phoebe, one of the moons of Saturn. These black particles relaunch the theory according to which rings would be the rests of the split moon.

The Cassini probe detected big quantities of oxygen around rings.
This phenomenon could explain by a collision which would have provoked this substantial separation of oxygen.

Image: Photography of Saturn's rings taken by the Voyager probe 2, on August 22nd, 1981.

The limit of Rock

What of what it is necessary to take into account it is the nearness of rings with regard to its planet.
Indeed the zone of rings is hardly situated between 60 and 200 000 km of the planet while Saturn has an equatorial diameter of 120 536 km. What explains the instability of its structures in rings.
Its structures of particles can thus exist only in a perimeter defined well inside the limit of Rock maintained by the strong attraction of the close planet. Near the planet, the strengths of attraction of the planet on two close particles is superior to the mutual attraction between both particles, what prevents the accretion of particles.
The distance in which these two effects nullify is called the limit of Rock. Beyond, the collisions bring particles to cling by accretion and to form a satellite. Since the Earth this structure seems homogeneous but closer rings show different bands.
Closer still, we would see uncountable free particles which would disappear very quickly if no mechanism maintained them in place. It is there that bring in in track satellites guards.
This role of sculptor and guard of these structures is mainly played by these satellites. The rings of Saturn have less than one kilometer in thickness and can locally, to be much thinner. Indeed, the collisions tend to reduce the perpendicular movements to the equatorial plan. The natural shape of a ring thus is to be flat and wide, to spread regularly until the limit of Rock.
All the objects going out of this zone are transformed into satellite. The origin of rings stays one of the most difficult problems which settles to the astronomers. As far as it is not about a unique phenomenon. Jupiter, Uranus and Neptune possess too systems of comparable rings.

Image: The photography opposite is constituted by an assembly of shooting begun by Travelling 2 at a distance of 21 million km.
Three visible satellites of Saturn to the left are from top to bottom: Tethys (1050 km in diameter), Dione (1120 km), and Rhea (1530 km).
To note the shadow of Tethys which forms a blackhead on the planet.