The universe is a big place. So big, in fact, that even our solar system, which is just a tiny speck in the grand scheme of things, is immensely vast and complex. Our solar system consists of eight planets, dozens of moons, and countless other celestial bodies, all orbiting around our sun. And for a long time, we thought that Pluto was one of those planets.
But then, in 2006, everything changed.
In August of that year, the International Astronomical Union (IAU) downgraded Pluto from a planet to a dwarf planet. This decision was based on new evidence that had been discovered about Pluto and its orbit. And while the IAU’s decision was controversial at the time, it is now widely accepted by the scientific community.
So why exactly is Pluto not a planet? Here’s a detailed explanation.
One of the main reasons why Pluto is not a planet is because of its orbit. Unlike the other planets in our solar system, which orbit around the sun in relatively flat planes, Pluto’s orbit is highly elliptical. In fact, it is so elliptical that at certain points in its orbit, it actually comes closer to the sun than Neptune does.
This strange orbit is due to the fact that Pluto is located in the Kuiper Belt, a region of the solar system beyond Neptune that is full of small, icy bodies. It is thought that Pluto was gravitationally pulled into its orbit by the planet Neptune.
Another reason why Pluto is not a planet is because of its size. Pluto is incredibly small, even smaller than our own moon. In fact, it’s so small that it’s only about two-thirds the size of Earth’s moon.
Pluto’s small size is due to its location in the Kuiper Belt. The further away from the sun a body is, the colder it is. And because Pluto is so far away from the sun, it is thought to be made mostly of ice.
Another reason why Pluto is not a planet is because of its composition. Unlike the other planets in our solar system, which are mostly made of rock and gas, Pluto is thought to be made mostly of ice. This is because Pluto is located in the Kuiper Belt, a region of the solar system that is full of small, icy bodies.
In 2015, NASA’s New Horizons spacecraft made a historic flyby of Pluto, giving us our first close-up look at the dwarf planet. And what we saw was a world that was very different from the other planets in our solar system. Pluto was found to be covered in a layer of methane and nitrogen ice, with a rocky core.
The IAU’s Definition of a Planet
One of the main reasons why Pluto is not a planet is because it does not meet the criteria set forth by the International Astronomical Union (IAU). In 2006, the IAU created a new definition of a planet, which states that a planet must fulfill the following three criteria:
- It must orbit around the sun.
- It must be massive enough to be rounded by its own gravity.
- It must have cleared the neighborhood around its orbit.
Based on this definition, Pluto does not qualify as a planet. This is because Pluto has not cleared the neighborhood around its orbit. Instead, it shares its orbit with a number of other bodies, including the planet Neptune.
The IAU’s decision to downgrade Pluto from a planet to a dwarf planet was controversial at the time. But in the years since, the scientific community has largely accepted the IAU’s decision.
So there you have it. Those are the reasons why Pluto is not a planet. It’s a fascinating world, to be sure, but it just doesn’t meet the criteria that we use to define a planet.