Saturn is the second largest planet. Only Jupiter is larger. Saturn has seven thin, flat rings around it. The rings consist of numerous narrow ringlets, which are made up of ice particles that travel around the planet. The gleaming rings make Saturn one of the most beautiful objects in the solar system. Jupiter, Neptune, and Uranus are the only other planets known to have rings. Their rings are much fainter than those around Saturn.
Saturn's diameter at its equator is about 74,900 miles, almost 10 times that of Earth. The planet can be seen from Earth with the unaided eye, but its rings cannot. Saturn was the farthest planet from Earth that the ancient astronomers knew about. They named it for the Roman god of agriculture.
Saturn travels around the Sun in an elliptical (oval-shaped) orbit. The planet takes about 10,759 Earth days, or about 29 1/2 Earth years, to go around the Sun, compared with 365 days, or one year, for Earth.
As Saturn travels around the Sun, it spins on its axis, an imaginary line drawn through its centre. Saturn's axis is not perpendicular (at an angle of 90 degrees) to the planet's path around the Sun. The axis tilts at an angle of about 27 degrees from the perpendicular position. Saturn rotates faster than any other planet except Jupiter. Saturn spins around once in only 10 hours 39 minutes, compared to about 24 hours, or one day, for Earth.
Surf ace and atmosphere
Most scientists believe Saturn is a giant ball of gas that has no solid surf However, the planet seems to have a hot solid inner core of iron and rocky material. Around this dense central part is an outer core that probably consists of ammonia, methane, and water. A layer of highly compressed, liquid metallic hydrogen surrounds the outer core. Above this layer lies a region composed of hydrogen and helium in a viscous form.
A dense layer of clouds covers Saturn. Photographs of the planet show a series of belts and zones of varied colours on the cloud tops. This banded appearance seems to be caused by differences in the temperature and altitude of atmospheric gas masses.
The plants and animals that live on Earth could not live on Saturn. Scientists doubt that any form of life exists on the planet.
The tilt of Saturn's axis causes the Sun to heat the planet's northern and southern halves unequally, resulting in seasons and temperature changes. Each season lasts about 7又1/2 儿Earth years, because Saturn takes about 29 times as long to go around the Sun as Earth does. Saturn's temperature is always much colder than Earth's, because Saturn is so far from the Sun. The temperature at the top of Saturn's clouds averages-285 degrees F (-175 degrees C).
Density and mass
Saturn has a lower density than any other planet. It is only about one-tenth as dense as Earth, and about two-thirds as dense as water. That is, a portion of Saturn would weigh much less than an equal portion of Earth, and would float in water.
Although Saturn has a low density, it has a greater mass than any other planet except Jupiter. Saturn is about 95 times as massive as Earth. The force of gravity is a little higher on Saturn than on Earth.
The rings of Saturn surround the planet at its equator. They do not touch Saturn. The seven rings of Saturn consist of thousands of narrow ringlets. Saturn's major rings are extremely wide. The outermost ring, for example, may measure as much as 180,000 miles across. However, the rings of Saturn are so thin that they cannot be seen when they are in direct line with Earth. They vary in thickness from about 660 to 9,800 feet (200 to 3,000 metres). A space separates the rings from one another. Saturn's rings were discovered in the early 1600's by the Italian astronomer Galileo. Galileo could not see the rings clearly with his small telescope, and thought they were large satellites. In 1656, after using a more powerful telescope, Christiaan Huygens, a Dutch astronomer, described a "thin, flat" ring around Saturn. In 1675, Giovanni Domenico Cassini, an Italian-born French astronomer, announced the discovery of two separate rings made up of swarms of satellites.
In addition to its rings, Saturn has 25 satellites that measure at least 6 miles (10 kilometres) in diameter, and several smaller satellites. The largest of Saturn's satellites, Titan, has a diameter of about 3,200 miles一larger than the planets Mercury and Pluto. Titan is one of the few satellites in the solar system known to have an atmosphere. Its atmosphere consists largely of nitrogen. Many of Saturn's satellites have large craters. For example, Mimas has a crater that covers about one-third the diameter of the satellite.
Flights to Saturn
In 1973, the United States launched a space probe to study both Saturn and Jupiter. This craft, called Pioneer-Saturn, sped by Jupiter in 1974 and flew within 13,000 miles of Saturn on Sept. 1, 1979. The probe sent back scientific data and close-up photographs of Saturn. The data and photographs led to the discovery of two of the planet's outer rings.
Pioneer-Saturn also found that the planet has a magnetic field, which is 1,000 times as strong as that of Earth. This field produces a large magnetosphere (zone of strong magnetic forces) around Saturn. In addition, data from the probe indicated the presence of radiation belts inside the planet's magnetosphere. The belts consist of high-energy electrons and protons, and are comparable to Earth's Van Allen belts.
In 1977, the United States launched two space probes一Voyager 1 and Voyager 2一to study Saturn and other planets. Voyager 1 flew within 78,000 miles of Saturn on Nov. 12, 1980. On Aug. 25, 1981, Voyager 2 flew within 63,000 miles of the planet.
The Voyager probes confirmed the existence of Saturn's seventh ring. They also found that the planet's rings are made up of ringlets. In addition, the probes sent back data and photographs that led to the discovery or confirmation of the existence of nine satellites. In 1997, the United States launched the Cassini probe to study Saturn, its rings, and its satellites. The probe began orbiting Saturn in 2004.
Answer the questions below using NO MORE THAN THREE WORDS from the passage for each answer.
1 Which is the biggest planet in the solar system?
2 How many Earth years does Saturn take to travel around the Sun?
3 How many minutes does Saturn take to rotate around each time?
4 What view probably results from the varied temperature and altitude of atmospheric gas?
5 What determines the force of gravity on a planet?
6 How many rings does Saturn have?
7 What are ringlets made up of?
8 Who first stated the ring around Saturn?
9 Why is one of Saturn's satellites, Titan, so special except for its large size?
10 What helped scientist discover the magnetic field of Saturn?