There are eight planets, many dwarf planets and their moon(s), asteroid belt, a large number of small bodies (the comets and asteroids) and interplanetary dust. The four inner planets Mercury, Venus, Earth and Mars are comparatively smaller in size and the terrestrial planets. They are primarily composed of metal and rocks. The four outer planets, Jupiter, Saturn, Uranus and Neptune are more massive than the terrestrials and are called gas giants. Jupiter and Saturn are two largest planets and are mainly composed of hydrogen and helium. Uranus and Neptune are two outermost planets and are composed largely of ices, such as water, methane and ammonia. They are known as ice giants.
Solar system was formed approximately 4.6 billion years ago from the collapse of a giant molecular cloud.
All planets in solar system move around Sun in a elliptical orbit with Sun at one focus. All planets orbit, except Mercury, are very nearly circular. All planets orbits are more or less in the same plane (called elliptic plane). The ecliptic plane is inclined with 7 degrees from the the Sun's equator plane.