Why did nine planets become eight planets? What do the eight planets have?

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Pluto didn't meet the criteria of a planet and was kicked out.

On August 24, 2006, the planet was discussed at the Prague meeting, excluded from the ranks of the nine major planets and officially downgraded to a dwarf planet.

Debate on Pluto's planetary qualification

When Pluto was first discovered, it was considered several times the size of the earth. Soon, Pluto was also written into textbooks as the ninth largest planet in the solar system. However, with the passage of time and the continuous upgrading of astronomical observation instruments, people increasingly found that the estimation at that time was a major "mistake" because its volume was much smaller than the original estimation. In addition, Pluto's planetary status has always been the focus of debate among astronomers because there has never been a specific and clear definition of a planet. Especially since the first discovery of the Kuiper Belt in 1992, more astronomical discoveries have intensified the debate on planetary qualifications.

This new discovery rekindled the debate.

2 1 century, the improvement of astronomical telescope technology has made people have a deeper understanding of Neptune celestial bodies. In 2002, an asteroid named 50000 Quaoar was discovered. The diameter of this newly discovered asteroid (1280 km) is more than half that of Pluto. In 2004, the asteroid named 90377 Sedna had a maximum diameter of 1800 km, while Pluto had a diameter of only 2320 km.

On July 9, 2005, another newly discovered celestial body besides Neptune was officially named Eris. According to its brightness and albedo, Eris is slightly larger than Pluto. This is the largest celestial body found in the solar system after the discovery of Neptune in 1846. Although * * * has no official knowledge, its discoverer and many media originally called it "the tenth planet". Some astronomers believe that the discovery of Eris provides strong evidence for rethinking Pluto's planetary status.

Even the salient features of Pluto-its satellites and atmosphere-are not unique. Some asteroids in Neptune's outer celestial belt also have their own moons. In addition, the spectral analysis of Eris shows that it has a surface similar to Pluto, and Eris also has a larger satellite, Mia, Snoww.

Resolution of the International Astronomical Union (IAU)-"Star Registration" for expelling Pluto

According to the resolution adopted by the International Astronomical Union on August 24, 2006, celestial bodies called planets must meet three main conditions.

1. This celestial body must be in orbit around the sun.

2. The celestial body must have enough mass to overcome the solid stress, so as to achieve the shape of hydrostatic balance (approximately spherical).

The celestial body must have cleared the area near its orbit.

Pluto, on the other hand, does not meet the third planetary standard mentioned above.

The International Astronomical Union further decided that Pluto should be classified as a dwarf planet and can be used as the prototype of an unnamed celestial body other than Neptune. Before this resolution, people also put forward different planetary schemes. Some even mentioned that besides Pluto, Mercury should be disqualified from being a planet on the earth, while others suggested that some asteroids should also be included in the planet list.

"New Vision" was launched in June 2006 at 5438+ 10, and it is expected to reach Pluto for observation at 438+05 in 2065.

Of the nine planets, Pluto is the farthest from the sun and has the smallest mass. It hobbles in the cold and dark space 5.9 billion kilometers away from the sun, which is very similar to proto, the god of the underworld in Roman mythology. So people call it Pluto, which is the first two letters of the English name of Pluto in astronomy, and the abbreviation of the name of Lovel, an American astronomer who promoted the discovery of Pluto.

Pluto is the latest planet to be discovered. Compared with the discovery of Uranus and Neptune, the discovery of Pluto is "a lot of trouble". Pluto's brightness is very weak, only 15 and so on. Even in the photos taken by large telescopes, it is no different from ordinary stars. Finding it among thousands of stars is like looking for a needle in a haystack.

In the process of searching for Pluto, Lovel, an American astronomer who is an astronomy enthusiast, calculated the position of this unknown planet in detail and searched it carefully with a telescope, which took more than ten years. Until19161.0616 suddenly died.

1925, Lovel's brother donated a large-field photographic telescope with a diameter of 32.5 cm, which provided excellent conditions for continuing the search for new planets.

From 65438 to 0929, the director of Lovel Observatory invited clyde william tombaugh to join the search for unknown planets. They searched and filmed one by one.

A large number of negatives, and carefully check each negative, the work is hard and boring. 193065438+1October 2 1 day, Tang Bo finally found this new planet in the negative of Gemini.

Mass: 0.0024 Earth mass

Radius:1350km

Period: 90465 days

Half-length diameter of orbit: 39.87 astronomical units.

Track eccentricity: 0.256

Orbit inclination: 17. 1.

Underground distance: 5.9 billion kilometers