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The solar system is made up of the sun, its planets, natural satellites, asteroids, meteoroids, and comets. Each of these bodies are held to each other by the force of gravity.
The sun is by far the most largest part of the solar system. . The other principal members of the solar system are the nine major planets.
The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The planets orbiting nearer the sun than the earth are called inferior planets; those whose orbits are larger are called superior planets. The unit for measuring distance in the solar system is the astronomical unit (A.U.), the average distance between the earth and the sun. The mean distances of the planets from the sun range from 0.39 A.U. for Mercury to 39 A.U. for Pluto.
The planets move almost in circular elliptical orbits based on the force of gravity. The sun's gravitational pull is the most powerful gravitational force in the solar system. The other heavenly bodies have a much smaller gravitational force on one another called perturbations.
The planets orbit the sun in the same counterclockwise direction. A planet's year is the time required for it to complete one full orbit around the sun. This is referred to as the planet's revolution. All the planets rotate about their own axes as they revolve around the sun
The planets are grouped according to their physical properties. The inner planets (Mercury, Venus, Earth, and Mars), are called the terrestrial (meaning earthlike) planets. They are dense and small in size. They have solid, rocky crusts and interiors of metal. Except for Mercury, they have gaseous atmospheres from which lighter elements have escaped because of the low gravitational force.
The Jovian planets (Jupiter, Saturn, Uranus, and Neptune) all have great volume and mass but relatively low density (thickness). Pluto has sometimes been classed with the terrestrial planets, but it is more properly considered a special case. Most of the nine major planets have one or more moons.