Saturn Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 16, 2011

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).

The Outer Planets Jupiter Composition, Atmosphere, And Weather

Figure 7-5. The equatorial diameter of Saturn is about nine times the diameter of Earth.

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 Rings

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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