The word planet is originated from the greek "planetai" and it means to roam. Even in the ancient times, people noticed that the movement of the planets are different from the stars. They appeared in other places in the sky in each season of the year. The five "roaming-planets" were known and had names even in the antiquity. Nowadays, people identify them with ancient roman mytholigic names:
The Uranus is the planet of the antiquity. It was discovered in 1781 by a german astronomer and optician,
William F. Herschel. Its name was given after the ancient greek mythological God of the Sky by Johann E. Bode.
We can put planets into two groups by the score of physical parameters.
The Earth-typed planets, wchich are similar to our planet are the first group. This type of orbs are usually made of rock containing metal and silicium. Their atmosphere generally contains harder elements like oxygen, nitrogen and carbon-dioxide. The Mercury due to its closeness to the Sun has lost its atmosphere.
The second group are the Jupiter-typed planets: the Jupiter, the Saturn, the Uranus and the Neptune. These are the giant gas-planets of the Solar system. The Pluto is different. Considering its size and composition, it can be counted as a moon of a giant planet. The giant planets have much weight than the Earth-typed ones. The loose gases can't leave their atmosphere due to the planet's huge gravity, so their atmosphere is mainly made of Hydrogene and Helium.