Why is pluto not a planet?

Understand flower parts

Pluto not a planet, Astronomers rule

According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.

Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.

The new definition also establishes a third class of objects that orbit the sun?"solar system bodies," which would apply to many asteroids, comets, and moons.

A previous proposal

The IAU proposal says that a planet is an object large enough to have become rounded due to the force of its own gravity.

But it's not that simple. What counts as a planet also depends on what it's orbiting around.

A planet has to orbit a star, so rounded objects floating freely through space won't make the cut.

But if an object is orbiting another, much larger object that's not a star, it wouldn't count as a planet either.

So Earth's moon, if it was orbiting the sun by itself, would qualify as a planet. But according to the proposed definition, since the moon circles Earth, it is actually a satellite.

The proposed definition also introduces two classes of planets.

The accepted eight planets?Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune?would simply be called planets.

But Pluto, its large moon Charon, and more distant objects would be called "plutons."

Plutons are all much smaller than the rest of the planets; they also have orbits that are tilted compared to the rest of the planets.

Pictorial view of the planets

3d models