Let's recall some important facts from school astronomy lessons:
Everyone knows about 8 well-known planets, but there are over than a hundred miniature worlds! They consist of the ocean of water, volcanoes, and lakes of liquid methane.
Planets which are made of dust and rock, such as Moon, are closer to the Sun. Liquid and gas planets are on the edge of the Solar system.
Pluto was considered as a planet before, but scientists confirmed that it is a dwarf planet now.
There is the Kuiper belt on the edge including comets and other dwarf planets.
There are still debates about the origin of Solar Systems. Scientists believe that it has been formed from the rotation of dust clouds and gas. Religious people know that God created the Universe. Big bang theory telling us about a huge explosion when a Life begins is still alive.
The asteroid belt is a space between Jupiter and Mars where thousands of bits of matter and comets orbit. Some of these pieces are no larger than a speck of dust.
For thousands of years, people believed that the Earth was at the center of the Universe. Only famous astronauts “opened eyes” to us explained how the planets are moving around the Sun, not opposite.
Why was Pluto excluded from the list of planets?
Until a few years ago, you had as many as 9 amazing solar system painting ideas, including Pluto. But in 2006, the 26th Assembly of the International Astronomical Union adopted a series of changes defining the concept of the term "planet", because of what Pluto lost its former status. So why exactly can we no longer see Pluto among the painted planets?
Earlier, until 2006, Pluto was considered the 9th planet, but its orbit deviates from the Ecliptic plane by 17 degrees and is flattened, which distinguishes it from the orbits of the other 8 planets of the solar system.
Plus Pluto is relatively small. Although it has 5 satellites, Pluto is 7 times lighter and 1.5 times smaller than the Moon. It was these characteristics that made scientists doubt, because Pluto is too different from other planets.
During the study of the Kuiper belt from 2004 to 2005, three more trans-Neptunian objects of similar size and orbits were discovered: Eris, Haumea, Makemake. It turned out that Pluto has more in common with these bodies than with the 8 planets. This changed the views of scientists and all previous solar system ideas. So there was a reason to combine these objects into a separate group. They are not asteroids, but they are not planets either.
Pluto is qualified to be a planet according to two characteristics. Its orbit, like other dwarf planets, is full of various other objects, including asteroids. Therefore, it was excluded from the list of planets and united into the group of Dwarf planets.
At the moment, the group of Dwarf planets includes: Pluto, Eris, Haumea, Makemake, and the former asteroid from the asteroid belt Ceres. Thus, the smallest planet Pluto became the largest planet in the group of Dwarf planets!