The sun is at the center of a huge rotating system of eight planets and five dwarf planets, their satellites, and many other smaller bodies. Each planetary body moves in an elliptical orbit in response to the sun’s gravitational force. All travel in the same direction around the sun. About 99.85% of the mass of our solar system is contained within the sun.
The planets fall into two groups. The terrestrial planets—Mercury, Venus, Earth and Mars—are relatively small and rocky. Earth is the largest of the terrestrial planets. The Jovian planets--Jupiter, Saturn, Uranus and Neptune – are enormous gas giants. Size is the most obvious difference between the terrestrial and Jovian planets. Density, chemical composition, and rate of rotation are other ways in which the two groups differ. The structure of the interiors of the two groups of planets and their atmospheres also set them apart. Pluto and Eris, the largest dwarf planet discovered in the January 2005, do not fit neatly into either category. Pluto, which is small and cold, was classified as a planet from its 1930 discovery until 2006. It is member of a distinct population called the Kuiper belt. Eris is a part of the scattered disc, a distant region of the solar system. Earth is unique among the planetary bodies of our solar system. Plate tectonics, at least the recycling kind that currently operates on our planet, is unique to Earth.
Although the planetary bodies of the solar system exhibit magnetism, not all have a magnetic field like Earth. Water exists at its surface in all three states—solid, liquid and gas. Water is an essential ingredient for life, as we know it. And life, at least terrestrial life, could not survive on Earth without the magnetic shield that protects us from the charged particles of the solar wind. Our Earth is a habitable planet.