Saturn is one of the most fascinating objects in the solar system, possessing many features that are unique among the known planets. Astronomers are regularly making new and surprising discoveries about this beautiful object, and its history is filled with the names of famous astronomers who have been drawn in by this planet more than any other. Here is a ‘Top 10’ of the most interesting things to know about Saturn:
~ 1. Discovery ~
Ancient civilizations were well aware that Saturn, like the four planets visible to the naked eye, was unlike the other points of light in the sky. Against the starry background, Saturn would move backward and forward, depending on the month. Because of its unique behaviour, it became in an important figure in many mythologies, and its modern name comes from the Roman god Saturnus.
In the 17th century, Galileo became the first person to observe the rings, although with his low power telescope he mistook them for a pair of moons. It took over 50 years of optical improvements before Christiaan Huygens proposed the existence of the rings in 1655.
~ 2. Position ~
Saturn is the sixth planet in the solar system, counting outwards from the sun. It is the second of the gas giants, smaller only than its neighbour Jupiter. Its orbit puts it about 1,400 million miles from the sun, which is 9.5 times the distance of earth’s orbit. It takes 29.5 years to complete a single orbit of the sun.
~ 3. Composition ~
Although Saturn is a gas giant, it still has a rocky core hiding deep below the surface. The chemical composition of this solid centre is probably similar to that of the earth. Surrounding this is a layer of liquid hydrogen and then a liquid hydrogen-helium mixture. Finally, there is an atmosphere 600 miles deep, which consists primarily of hydrogen gas, with just over 3 percent helium and some trace elements which help form icy ammonia clouds.
~ 4. Density ~
Saturn has a diameter 9.5 times that of Earth and its mass is about 95 times greater. However, because the planet consists primarily of hydrogen, its density is only 70 percent of that of water. This means that Saturn would float if you could find a bath big enough to put it in. All the other planets would sink.
~ 5. Rotation ~
Saturn’s year might be long, but its day is only 10.5 hours long. Because its spinning so quickly, it bulges significantly about the equator. The equatorial circumference is 10 percent larger than the polar circumference.
Defining Saturn’s rotation is actually quite a difficult task. Because the planet is not solid rock, like the earth, different regions can rotate at different speeds. Winds at the equator blow at over 1,000 kilometres an hour, and the rotational period in this central band is shorter than regions closer to the poles. Probes have also measured the rotation of the magnetic field of the planet, and this is even slower. Interestingly, recent Cassini measurements show that the magnetic field is 6 minutes slower than it was when the Voyager missions passed Saturn 30 years ago.
~ 6. Moons ~
At the last count (Jan. 2011) Saturn has a bewildering 62 moons, only 53 of which actually have names. Over half of these moons are less than six miles in diameter, and scientists are regularly discovering new ‘moonlets’ as they probe Saturn’s rings.
As new moons are identified, they are given a code to identify them until a name is chosen. Traditionally, the moons of Saturn were named after Titans of Greek mythology. However, the sheer number of moons discovered recently means the IAU has had to dip into other mythologies to provide names. The 29 ‘Nordic’ moons are interesting, as they have a retrograde orbit, meaning they circle in the opposite direction to the other moons, and to the planet’s rotation.
Uniquely in the solar system, Saturn has ‘Trojan moons’. These are small moons that share an orbit with a larger satellite, always remaining at exactly the same separation from the larger body.
The largest of Saturn’s moons is the mighty…
~ 7. Titan ~
Titan is a giant, and one of the most exciting objects in the solar system. The only larger moon is Jupiter’s Ganymede. Titan is larger than Mercury, although its lower density means it is less heavy.
It is the only moon in the solar system with a proper atmosphere. Like our atmosphere, it is mostly nitrogen, although the rest is methane rather than oxygen. The Cassini probe has observed clouds in the atmosphere, although it is far too cold for water clouds to form. It is likely that they consist of methane or ethane.
On the surface, lakes of liquid methane wash against icy shores. This makes Titan the only body in the solar system, other than Earth, to have stable bodies of liquid, and consequently one of the most likely places to find extra-terrestrial life.
~ 8. Visits ~
Unmanned probes have visited Saturn a number of times. Pioneer 11 was first to arrive in 1979. It was closely followed by Voyager 1 and Voyager 2, on their way to the edge of the solar system. All three provided valuable information on the rings and moons.
In 2004, the Cassini-Huygens probe arrived, and settled into permanent residency around the planet. It has been returning valuable scientific data ever since, and although its primary mission has finished, it is hoped that data will keep arriving until at least 2017. One of the highlights of the probe’s visit was the release of the Huygens probe into the atmosphere of Titan. It provided data from its 2.5 hour descent and even sent back pictures of the surface.
~ 9. Polar Patterns ~
When Voyager 1 passed by, it sent back pictures of Saturn’s north pole. Scientists were surprised to discover a hexagonal cloud formation, larger than the earth, circling the pole. How this pattern was formed, and how it is maintained, are still a subject of debate.
~ 10. Rings ~
Saturn’s most extraordinary feature is, of course, the rings. They span a distance of 68,000 miles from about 4000 to 72000 miles above the atmosphere. Despite this, the rings have an average thickness of just 20 metres! Most of the material in the rings is frozen water, and the particles range in six from dust to about two metres, with the occasional moonlet. Opinion is divided on the origin of the rings. One possibility is that the material is the remnants of a destroyed moon, but it is also possible that it is just left over material from Saturn’s formation.
The ring structure is rich in detail as particle density and reflectivity changes with altitude. The moons and moonlets help herd the rings, keeping some orbits completely free of material, while crowding the particles in other orbits. Different sections are named, as are the gaps between them, such is the interest in the rings.
Sources:
http://saturn.jpl.nasa.gov/science/moons/
http://saturn.jpl.nasa.gov/index.cfm
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn
