Saturn Help (page 2)
Introduction to Saturn
In mythology, Saturn is the Roman god of agriculture. The name also refers to the father of the Greek god Zeus. Because Zeus and Jupiter are the same entity, Saturn might well be attached in mythology with an importance equal to or greater than that of Jupiter. Jupiter is Saturn’s mythical son; without Saturn, Jupiter would never have been born, or would have turned out much different. (Of course, this is only according to the ancient myths; we know better than to believe that those tales are true.)
Before telescopes revealed the ring system, the name Saturn was associated with old age and dullness. If it were not for the rings, Saturn would indeed be a somewhat less interesting version of Jupiter, at least from an observational point of view.
The Year And The Day
Saturn orbits the Sun at a distance of 9.54 AU (Fig. 7-4). It orbital radius is about 1,430 million kilometers (888 million miles). The best viewing of Saturn is done when the planet is at opposition. Saturn is almost twice as far away from the Sun as is Jupiter, and the ringed planet receives only 1.1 percent as much sunlight per unit area as Earth. Saturn reflects sunlight well, and this is enhanced by the ring system. Saturn looks similar to Jupiter with the unaided eye but is somewhat dimmer, comparing favorably with Mars most of the time. Saturn is easy to relocate once you have found it on any given night.
Saturn, like Jupiter, does not pass through phases; it always appears full or almost full. Its brilliance in the sky, as we see it, changes because its distance from us varies. In general, the greater the angle between Saturn and the Sun, the brighter Saturn appears as seen from Earth. The brilliance of Saturn is also affected by the angle at which the rings are presented to us. If the rings are edge-on, the planet looks dimmer at a given distance from us than if the rings are seen from above or below. Saturn takes 29½ Earth years to make a complete revolution around the Sun with respect to the distant stars. Thus Saturn reaches an opposition approximately once every 12½ Earth months.
Saturn, like Jupiter, rotates rapidly on its axis. The complete day, midnight to midnight, lasts for about 10 hours and 40 minutes Earth time, as determined by observations of the magnetic field. The planet’s upper clouds rotate slightly faster than this at latitudes near the equator. Near the poles, the atmosphere appears to rotate at about the same speed as the planet’s magnetic field.
Composition, Atmosphere, And Weather
Saturn might be considered a little brother (rather than the father) of Jupiter on casual observation, were it not for the ring system. Saturn is almost as large as Jupiter. At the equator, Saturn’s diameter is 121,500 kilometers (75,500 miles), more than nine times that of Earth (Fig. 7-5).
Saturn is comprised of about three-quarters hydrogen and one-quarter helium, with trace amounts of ice, methane, ammonia, and silicate molten rock. The inner core is where this mineral matter is found; if all the hydrogen and helium on Saturn were blown away, the remaining body would be a planet similar to Earth but several times more massive. As with Jupiter, the inner core is surrounded by liquid metallic hydrogen mixed with helium. As we progress further and further from the center of the globe, the liquid hydrogen becomes nonmetallic; then it becomes a dense gas, thinning out and topped with the yellowish clouds we see from a distance.
The rather bland appearance of Saturn’s cloud bands, compared with those of Jupiter, belie the violent winds that continuously blow around Saturn. At their strongest, these winds are several times hurricane force on Earth. Vortices (eddies) occur on Saturn, but they are less visible than those on Jupiter because the upper cloud layer is more uniform and makes it difficult to see what is going on further down.
Saturn’s equator is slanted by 26.7 degrees relative to the plane of its orbit around the Sun. Thus Saturn has seasons of a sort, although the deep and windy atmosphere tends to equalize the temperatures between the equator and the poles. An observer on Saturn, supposing that it were possible to exist there, would notice changes in the amount of daylight for each rotational cycle; “winter days” would be much shorter than “summer days.” However, no one will ever go to Saturn and experience these seasonal fluctuations. It is believed that Saturn has no definable surface on which to land, and merely contending with the violent winds would totally preoccupy anyone venturing below the cloud tops. If Saturn did have a surface—liquid hydrogen, say, like an ocean—any ship that set sail there would be plucked up instantly and whisked away into the darkness like a toy boat in a tornado.
The outer atmosphere of Saturn is about 90 percent hydrogen. This means that the interior must contain relatively more helium. Some scientists believe that helium is constantly precipitating down toward the center of Saturn, in much the same way as the heavier components in a vinegar-and-oil salad dressing settle out. This process apparently has been going on ever since the birth of the Solar System and contributes to Saturn’s internal heat.
The ring system of Saturn, as we see it from Earth through telescopes, is about 250,000 kilometers (155,000 miles) in diameter. The rings are extraordinarily thin in proportion to their width. The drawing of Fig. 7-5 greatly exaggerates the thickness of the rings. If the drawing were true to scale in this respect, with the rings viewed edge-on, they would not be visible without a magnifying glass. Estimates of the rings’ thickness range between 100 meters (about 300 feet) and 1 kilometer (about 3,000 feet). The only reason we can see them from Earth is that they are excellent reflectors of light.
Even before the rings of Saturn were photographed at close range by space probes, scientists knew they were comprised of countless chunks of icy material, ranging in size from grains of dust to boulders bigger than a house. They could figure this out because of what the rings do to electromagnetic waves from distant stars, galaxies, and other sources passing through the ring system. The number of particles is inversely proportional to their size; that is, there are far more tiny grains than medium-sized rocks and far more medium-sized rocks than large boulders.
The ring system presents several mysteries. Astronomers think they have solved some of these, but others remain inexplicable. One theory holds that the rings formed from the breakup of an icy moon that ventured too close to Saturn and was torn apart by gravitational forces. Every planet’s gravitational field, even that of the Earth, has a minimum orbital radius within which large natural satellites cannot stay in one piece. This is known as the Roche limit . For Saturn, the Roche limit is roughly 2½ times the radius of the planet. Boulder-sized rocks and even a few small asteroids continue to orbit Saturn in one piece within this limit; the maximum limiting size depends on what the particle is made of. There are a few especially large boulders that orbit Saturn inside the ring system, and these are believed to be responsible for the gaps , also called divisions , that appear in the ring system.
Practice problems of this concept can be found at: The Outer Planets Practice Problems
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