THE SOLAR SYSTEM

The solar system consists of the Sun; the nine planets, 67 satellites of the planets and a large number of small bodies (comets and asteroids). The inner solar system contains the Sun, Mercury, Venus, Earth and Mars: The planets of the outer solar system are Jupiter, Saturn, Uranus, Neptune and Pluto: The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury and Pluto are very nearly circular. The orbits of the planets are all more or less in the same plane. The ecliptic is inclined only 7 degrees from the plane of the Sun’s equator. Pluto’s orbit deviates the most from the plane of the ecliptic with an inclination of 17 degrees.
The Sun: The sun is the most important part of our solar system. It is the biggest object and does have about 98% of the whole mass of the solar system. Almost uncountable earths would fit inside the sun. The sun travels around the galaxy together with planets and other objects bound to it by gravitational forces. The largest of the bodies we call planets, most of which are in turn are orbited by smaller moons or satellites. These objects, together with many lesser masses, are known as the Solar system. The Sun is just a star, one of a hundred billion inhabiting our galaxy alone. Being a star the Sun is an example of the fundamental building blocks of our universe. It formed, 4.5 billion years ago, as the nucleus of a cloud of gas which was collapsing under its own gravitational attraction. At formation, hydrogen was the most abundant gas, as elsewhere in the universe, and accounted for three quarters of the Sun’s original material. This will changes as the hydrogen is burned, and within the very central regions virtually all the hydrogen has been converted to helium.
Mercury: Mercury is named after the messenger of the Roman gods. It is the smallest of the inner planets and the second smallest in the whole Solar System. It has a very weak magnetic field and—being the closest planet to the Sun—has only a very thin atmosphere of helium captured from the solar wind. The surface of Mercury is very much like the Moon’s—with craters, mountains and valleys. Since there is no form of atmosphere, life on Mercury is impossible. Although Mercury has only a third the diameter of Earth, its density is about the same.
Venus: Venus is named after the Roman goddess of love. It is the second planet from the Sun and the brightest object in the sky other than the Sun and the Moon. It was once believed that life could exist in Venus but that has been proved wrong by various probes. In fact, Venus has the most hostile environment in the entire Solar System. The surface temperature is fiercely hot and the atmospheric pressure is crushing. One of the more apparent things that separate Venus from all the other planets in our solar system is that it rotates from east to west (all the other planets rotate from west to east). Because of this, Venus is said to be almost upside down.
Earth: The Earth, the third planet from the Sun, is the largest of the inner planets and also has the highest density. It is the only planet in the Solar System to be covered largely with water, the only planet with an atmosphere made up chiefly of nitrogen and oxygen and the only body that has a temperature suitable for life of the type that we know. It is also the only inner planet with a large moon. If the conditions on the Earth changed even slightly, the life as we know it could die out. The Earth’s rotation period is not constant. It is slowly lengthening due to tidal friction between the oceans and the sea floor. This is caused by the influence of the Moon.
Moon: The Moon has fascinated mankind throughout the ages. By simply viewing with the naked eye, one can discern two major types of terrain: relatively bright highlands and darker plains. Current knowledge of the Moon is greater than for any other solar system object except Earth. This lends to a greater understanding of geologic processes and further appreciation of the complexity of terrestrial planets. The relatively bright, heavily cratered highlands are called terrae. The craters and basins in the highlands are formed by meteorite.
Mars: Mars is the fourth planet from the Sun and the seventh largest. Mars is sometimes referred to as the Red Planet. The name of the month March derives from Mars. Mars has been known since prehistoric times. Except for Earth, Mars has the most highly varied and interesting terrain of any of the terrestrial planets. Like Mercury and the Moon, Mars appears to lack active plate tectonics at present; there is no evidence of recent horizontal motion of the surface such as the folded mountains so common on Earth.
Jupiter: Jupiter is named after the king of the Roman gods. It is the largest planet in the Solar System, the fifth planet from the Sun and the first of the outer planets Jupiter has had a dominant effect on a large part of the Solar System. It is likely that Jupiter’s huge gravity has prevented a planet from forming in the area now occupied by the Asteroid Belt. Jupiter has a magnetic field 20,000 times stronger than that of the Earth’s, having a devastating effect on its moons.
Saturn: Saturn is the sixth planet from the Sun and the second largest: In Roman mythology, Saturn is the god of agriculture and has been known since prehistoric times. Galileo was the first to observe it with a telescope in 1610; he noted its odd appearance but was confused by it. Early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn’s rings every few years as Saturn moves in its orbit Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and rock.
Uranus: Uranus is the forth largest planet in the Solar System and the seventh from the Sun. Named after the father of Saturn, Uranus is a blue-green colour due to the methane in its atmosphere. Its magnetic axis is at 60 degrees to its axis of rotation. The unusual axial tilt may have been caused by a collision by a large body early in Uranus’ life.
Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium.
Neptune: Neptune named after the Roman god of the sea was discovered using mathematic calculations based on the orbit of Uranus. It is the third largest planet in the Solar System and is usually the second last planet in distance. Because of Pluto’s eccentic orbit, Neptune is the last planet for 20 years every 247 years. Neptune was the last planet until recently, when Pluto past it with its orbit and became the last planet again.
Pluto: Pluto was discovered on February 18, 1930, making it the last planet found in our Solar System. Pluto is usually farther from the Sun then any of the nine planets. Ground-based observations indicate that Pluto’s surface is covered with methane ice and that there is a thin atmosphere that might freeze and fall to the surface as the planet moves away from the Sun. Pluto has one moon— Charon—its surface composition seems to be different from Pluto’s. The moon appears to be covered with water-ice rather than methane ice. Its orbit is gravitationally locked with Pluto, so both bodies always keep the same hemisphere facing each other.
Asteroids: Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets. They are known as minor planets. Sixteen asteroids have a diameter of 240 km or greater. They have been found inside Earth’s orbit to beyond Saturn’s orbit. Most, however, are contained within a main belt that exists between the orbits of Mars and Jupiter. Asteroids are material left over from the formation of the solar system.