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Solar System, page 1 Astronomy - The Solar System, 2 of 2 Sun

Sun and the nine planets

All matters of the Solar System almost contain entirely in the Sun, about 99.85 %. The eight planets, together with Pluto, only consist of 0.135 % of the total mass while the remaining 0.015 % constitute of planets' satellites, comets, asteroids, solar particles, dusts etc. The planets can be divided into two gropus: (i) The Terrestrial Planets, consist of four planet closest to the Sun: Mercury, Venus, Earth and Mars. (ii) The Jovian Planets, consist of the following four planets: Jupiter, Saturn, Uranus and Neptune. The Terrestrial Planets are generally compact and rocky, whereas the Jovian Planets are comparatively much bigger in size and gaseous in nature. These planets are also sometimes referred to as the gas giants.

The distances of the Terrestrial Planets from one another and from the Sun are relatively close when compare with those of Jovian Planets. Diagram below shows relative (approximate) size of planetary orbits.
Solar System
Beside planets, there are many millions more objects that orbit the Sun such as asteroids and comets. Most asteroids are located at the Main Asteroid Belt, located between Mars and Jupiter. However, some orbit between Saturn and Uranus or even as far away as Pluto and beyond.

In 1950, J. Oort (1900-1992), a Dutch astronomer, found that all comets orbit the Sun and none came from interstellar space and there is no preferential direction from which comets come. This led to a speculation that comets may have originated from a vast cloud surrounding the outer reaches of the Solar System. However, the existence of such cloud, known as the Oort Cloud, is yet to be confirmed. In addition, it is believed there exists a vast disk-shape region called the Kuiper Belt, with a distance of 30AU from the Sun and extended to 100AU. This places the belt beyond Neptune and extends beyond Pluto. As of the year 2000 there are three hundred objects have been discovered from this region of space. In fact, some argue that Pluto may be one of the largest example of Kuiper object and hence not a proper planet. However, there is no intention to 'demote' Pluto's official designation as a planet to a Kuiper object.

Solar system, page 1 Sun


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