1, Mercury: Mercury is the closest planet to the sun and one of the smallest planets in the solar system. Its surface temperature is extremely hot during the day and extremely cold at night. Because there is no atmosphere to keep heat, its surface temperature varies greatly.
2. Venus: Venus is the closest planet to the Earth in the solar system. It is called the sister planet of the earth because it is similar in size and mass to the earth. However, Venus is the hottest planet in the whole solar system because of its extremely harsh surface conditions, thick carbon dioxide atmosphere and extremely high temperature.
3. Earth: The Earth is our home. It is the only known planet with life in the solar system. It has a climate and conditions suitable for life, so it is called the blue planet.
4. Mars: Mars is the fourth planet in the solar system and a close neighbor of the earth. Its surface is red and it is called the red planet. At present, scientists are exploring Mars to find out whether there are signs of life in the past or now.
5. Jupiter: Jupiter is the largest planet in the solar system, and its volume exceeds the sum of all other planets and satellites. It is a huge gas planet with an amazing red spot and many annular zones.
6. Saturn: Saturn is famous for its beautiful optical ring system. It is the sixth planet in the solar system. Similar to Jupiter, Saturn is also a gas giant planet, and its ring is composed of ice and rock fragments.
7. Uranus: Uranus is the seventh planet in the solar system. This is a huge gas planet. Unlike other planets, Uranus' axis of rotation is very inclined, which causes its north pole and south pole to face the sun in different seasons.
8. Neptune: Neptune is the eighth planet in the solar system and the farthest gas planet from the sun. It is a blue planet with strong storms and atmosphere.
9. Pluto: Pluto was once considered as the ninth largest planet in the solar system, but it was reclassified as a dwarf planet by the International Astronomical Union in 2006. It is one of the smallest and coldest objects in the solar system, which is located outside the orbit of Neptune.
Basic introduction of nine planets
New astronomical discoveries have questioned the traditional concept of "nine planets". American astronomers misjudged Pluto's mass and listed it among the "Nine Planets". Later, it was found that Pluto did not meet the definition of planet, so it was kicked out of the "nine planets", leaving only eight planets in the solar system.
Astronomers have discovered some differences between Pluto and other planets in the solar system. Pluto's orbit is outside Neptune and belongs to the Kuiper Belt outside the solar system. This area has always been a gathering place for asteroids and comets in the solar system today.
Since 1990s, astronomers have found that there are more celestial bodies orbiting the sun in the Kuiper Belt, and each value is larger than Pluto. For example, American astronomer Brown discovered "2003UB3 13" (terbium star: diameter 2326 12km, slightly smaller than Pluto. But its mass is 127% of Pluto's, and it is a celestial body with more mass than Pluto. Therefore, it is not difficult to understand the change from "nine planets" to "eight planets", otherwise the solar system will be flooded by planets.