Why was Pluto excluded from the list?

Pluto is excluded from the list because it doesn't conform to the definition of a planet and can't form a hydrostatic balance, and its trajectory intersects with Neptune's trajectory, so it doesn't conform to the trajectory conditions of other celestial bodies. At first, it was named the Top Ten Planets because it misjudged the mass of Pluto. Later, after research and investigation, Pluto was removed from the list.

1930, clyde tombaugh discovered Pluto and regarded it as the ninth planet. After 1992, some celestial bodies with similar mass to Pluto began to challenge its planetary status.

The mass of Mars discovered in 2005 is even 27% more than that of Pluto, so the International Astronomical Union (IAU) officially defined the concept of planet in 2006, excluding Pluto from the list of planets and reclassifying it as a dwarf planet.

Extended data:

Pluto's rotation period, that is, its day, is equal to 6.387 Earth days. Pluto, like Uranus, rotates laterally on the orbital plane, with an axis inclination of 120 degrees, so the seasons vary greatly. On the solstice (summer solstice and winter solstice), one quarter of its surface is in extreme day state, while the other quarter is in extreme night state.

The reason for this unusual rotation direction is controversial. Research by the University of Arizona shows that this may be because celestial bodies always adjust their rotation direction in a way that minimizes energy.

This may mean that the celestial body will change its direction of rotation, placing excess mass near the equator, while areas lacking mass will tend to the poles.