what are reasons for excluding pluto from planet's list?

Question

recently it was decide that pluto is not a planet & is merely a satellite , so how the decide for this decision after so many years?

Answer 1

It's too similar to a lot of "Kuiper Belt Objects" in the same region. If you called it a planet, you'd have to include a lot more planets.

The same thing happened before. Ceres was called a planet until people started finding many more asteroids. They stopped calling it a planet because otherwise they'd have to call a lot more things planets.

The eight recognized planets are way more unique in the Solar System. Ceres and Pluto were just the first discoveries of two large groups of similar objects, asteroids and KBOs.

Answer 2

Mike Brown of Caltech and his colleagues have recently proposed that population of small bodies which may share the orbit with the candidate body should be taken into account when defining a planet. They propose that if a body's mass is greater than the total mass of small stuff which orbits in the same region, it is a planet. So, Mercury might not be too big, but since very few asteroids orbit the Sun in its vicinity, it is definitely a planet. Jupiter shares its orbit with numerous so-called Trojan asteroids, but their total mass is negligible compared with that of Jupiter, so Jupiter is also a planet. Pluto, according to this criterion, is not a planet, because its mass is smaller than the estimated total mass of all other Kuiper Belt Objects.

The theory behind this definition is that once an object is large enough it would "sweep up" smaller bodies in its vicinity, leaving its orbit empty except for itself, few transient interlopers (comets etc.) and maybe a resonant population with a small mass (e.g. Trojans). Eight major planets managed to do this, but not Pluto, which is not a major influence on the Kuiper Belt.

Answer 3

it has a characteristics of a planet. it was changed because of what have people studied.