The order of planets from inside to outside is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury, Venus, Earth and Mars near the sun are called terrestrial planets.
Their common characteristics are high density (>: 3.0g/cm3), small volume, slow rotation and few satellites, which are mainly composed of silicate and have a solid shell. Jupiter, Saturn, Uranus and Neptune, which are far away from the sun, are called woody planets.
Their common feature is low density (
Extended data
There is an asteroid belt between Mars and Jupiter, which contains hundreds of thousands of asteroids (that is, irregular small stars made of rocks). It is speculated that they are rock fragments between Mars and Jupiter that have not yet accumulated into planets.
Meteorites exist between planets and are made of stone or iron. The meteorite introduced in the chapter on earthquakes and the internal structure of the earth is the meteorite fragments that fell on the earth.
There is a comet "warehouse" in the annulus between Neptune's orbit and the sun's distance of 40~50 astronomical units, which is estimated to contain 1 billion ~ 1 trillion comets, called the Kuiper Belt. Comets are mainly composed of water, carbon dioxide, carbon monoxide, ammonia, methane and other ice, mixed with dust particles, usually ranging in size from several hundred meters to several tens of meters.
Comets orbiting the sun in the Kuiper Belt are sometimes influenced by the gravity of other celestial bodies and fly into the solar system along a flat elliptical orbit. When they are close to the sun, they are heated by sunlight, and gas and dust are volatilized from comets, forming tails under the action of solar wind and sunlight.
Baidu encyclopedia-solar system