GEOLOGY - Universe and the Solar System

The earth on which we are living is a 'remarkable' astronomical body in the entire universe , even though it is neither the largest or the heaviest , nor the fastest or the slowest member of our solar system. It is , intact , a very insignificant component of our solar system , which consist of nine major planets (including the earth) moving around a central body - the sun. Besides these nine major planets, there are 32 moons or satellites , vast number of asteroids , thousands of comets , and innumerable meteors , which constitute the integral part of our solar system. The nine major planets and their moon's are revolving in nearly the same plane around the sun. In addition to this movement around the sun , these planets are undergoing constant rotation about their own axis. The inner four planets , in the order of increasing distance from the sun are :-
(1) Mercury
(2) Venus
(3) Earth
(4) Mars

The outer group consists of :-
(5) Jupiter
(6) Saturn
(7) Uranus
(8) Neptune and
(9) Pluto.

The four inner planets are also known as terrestrial planets because they are about the same size , and their density suggests a composition of iron and stone. They are , thus , characterised by relatively smaller mass , much higher average density and faster speeds of rotation. These four planets have also been referred to as minor planets. The five outer planets are the major planets which reassemble the terrestrial planets , but are usually treated as a separate group. They are characterised by heavy mass , much lighter in average density , and sluggish in speeds of rotations.
Astrologers agree that all the major planets have already been discovered. The latest and the most recent discovery was that of the planets Pluto , the farthest planet from the sun , and whose position in space was predicted by astronomers more than a decade before the actual discovery in 1930. The only planet , for which no moon's are known are Mercury , Venus and Pluto. The earth has only one , whereas Saturn has ten , and Jupiter has twelve ; Mars and Neptune have two each , and Uranus has five.
Even inspite of the fact that the earth is a very insignificant component of our solar system , and much more insignificant part of our universe , it has been termed as 'remarkable' , mainly because of the fact that out of billions of celestial objects in the universe , it is the only body which is certainly known to support life , as we know it today. It also becomes of important to us because it is our home and we live on it.  It also becomes important to us because it is our home and we live on it.

-: Satellites or Moon's are those celestial bodies , each of which are revolving around any of these nine planets.

-: Asteroids are the minor planets , generally situated between the orbits of Mars and Jupiter. The largest of these bodies probably exceeds 700 km in diameter , and the smallest visible Ones are 2 to 3 km across.

-: Comets are the heavenly bodies having a long tail pointing approximately away from the sun , and a brighter head section that contains a small bright nucleus.

-: Meteors are smaller solid bodies moving through the space , and getting illuminated while entering earth atmosphere.