Pluto was reclassified from a planet to a **dwarf planet** in 2006 due to a new definition of what constitutes a planet, as set by the **International Astronomical Union (IAU)**. Before that, Pluto was considered the ninth planet in the solar system since its discovery in 1930. However, advances in astronomy and the discovery of similar objects led scientists to reconsider Pluto's status. Here's a breakdown of the reasons why Pluto is no longer classified as a planet:

### 1. **IAU's Definition of a Planet**
In 2006, the IAU established three specific criteria that an object must meet to be considered a planet:

1. **It must orbit the Sun**.
2. **It must be spherical in shape**, meaning it has enough mass to achieve hydrostatic equilibrium (its own gravity pulls it into a roughly round shape).
3. **It must have cleared its orbit**, meaning it has become gravitationally dominant in its orbit and cleared out any other objects near it.

Pluto meets the first two criteria:
- It **orbits the Sun**.
- It is **spherical** due to its mass and gravity.

However, Pluto does **not** meet the third criterion. This is the main reason for its reclassification.

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### 2. **Pluto Hasn't Cleared Its Orbit**
Pluto orbits within the **Kuiper Belt**, a region beyond Neptune filled with many icy bodies and debris. Unlike the eight recognized planets, Pluto shares its orbit with other objects of similar size, including other dwarf planets and small celestial bodies. Therefore, it has not "cleared" its neighborhood of debris.

In contrast, planets like Earth or Jupiter have become the dominant objects in their orbits, having cleared away most of the debris and smaller bodies through gravitational interactions over billions of years.

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### 3. **Discovery of Similar Objects in the Kuiper Belt**
The discovery of other objects in the Kuiper Belt similar to Pluto, such as **Eris**, which is actually more massive than Pluto, raised questions about how Pluto was classified. If Pluto were to remain a planet, many other similar objects would also qualify as planets. This led astronomers to rethink the definition of a planet and introduced the need for clearer classification.

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### 4. **The Creation of the Dwarf Planet Category**
In response to the discoveries of Pluto-like objects, the IAU created the category of **dwarf planets** in 2006. According to the IAU, a **dwarf planet** is defined as an object that:
- Orbits the Sun.
- Is spherical in shape due to its own gravity.
- **Has not cleared its orbit** of other debris.

Pluto fits this definition, making it one of the most well-known dwarf planets. Other dwarf planets include **Eris**, **Haumea**, **Makemake**, and **Ceres** (the largest object in the asteroid belt between Mars and Jupiter).

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### 5. **Pluto's Orbit is Highly Eccentric and Inclined**
Pluto's orbit is more eccentric (elliptical) and inclined compared to the orbits of the eight planets. Its orbit crosses Neptune’s, and it is tilted at an angle relative to the plane in which most planets orbit. This irregularity further separates Pluto from the typical characteristics of the eight major planets.

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### Conclusion: Why Pluto Isn't a Planet
Pluto is no longer classified as a planet primarily because it hasn't cleared its orbit of other objects, a key requirement in the IAU’s definition of a planet. Its reclassification as a **dwarf planet** better reflects its characteristics and distinguishes it from the larger, more dominant planets in the solar system. Despite this change, Pluto remains an important and fascinating object in astronomy, especially as it helps scientists learn more about the outer regions of our solar system.