In lower classes, all of us must have studied that our Solar System has Nine Planets. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The inner planets (in order of distance from the sun, closest to furthest) are Mercury, Venus, Earth and Mars. After an asteroid belt comes the outer planets, Jupiter, Saturn, Uranus, Neptune, and Pluto. THIS IS WRONG FRIENDS!!!

Many of us don’t know that Pluto is no longer a planet. This is because, the International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet. Before we go to the reason, let us learn something more about Pluto.

 About Pluto 

• Pluto was discovered in 1930 by US astronomer Clyde Tombaugh, who was using the Lowell Observatory in Arizona.
• From 1930 until 2006, Pluto sat comfortably beyond Neptune as the ninth planet in our solar system.
• Pluto was known as the smallest planet in the solar system and the ninth planet from the sun.
• Pluto was named by an 11-year-old girl from England.
• Pluto has five moons. Its largest moon is named Charon (KER-ən). Charon is about half the size of Pluto.
• Pluto’s four other moons are named Kerberos, Styx, Nix and Hydra.
• Pluto is very, very cold. The temperature on Pluto is 375 to 400 degrees below zero.
• Pluto has about one-fifteenth the gravity of Earth. A person who weighs 100 pounds on Earth would weigh only 7 pounds on Pluto.
• It takes approximately 248 Earth years for Pluto to make one trip around the sun. Since astronomers discovered Pluto in 1930, it has not completed one trip around the sun. It still has more than 150 Earth years to go!
• Pluto is so far away that it takes more than five hours for light from the sun to reach it. The sun’s light reaches Earth in only eight minutes!

 Finding of Eris 

In 2003, an astronomer saw a new object beyond Pluto. The astronomer thought he had found a new planet. The object he saw was larger than Pluto. He named the object Eris (EER-is).

Finding Eris caused other astronomers to talk about what makes a planet a “planet.” There is a group of astronomers that names objects in space. This group decided that Pluto was not really a planet because of its size and location in space. So Pluto and objects like it are now called dwarf planets.

Four of the dwarf planets — Pluto, Makemake, Haumea and Eris — are located beyond Neptune. The fifth dwarf planet, Ceres, lives in an asteroid belt between Mars and Jupiter.

 What are the New Rules? 

According to new rules adopted by the International Astronomical Union, a celestial body must meet the following criteria in order to qualify as a planet:

1. A planet must be round.
2. A planet must orbit the sun.
3. A planet must have “cleared the neighborhood” of its orbit.

 What does “cleared its neighborhood” mean? 

As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Pluto follows the first two rules: It is round, and it orbits the sun. It does not, however, follow the third rule. It has not yet cleared the neighborhood of its orbit in space. Because it does not follow this rule, Pluto is no longer considered a planet.

 What is a Plutoid? 

Pluto is also called a plutoid. A plutoid is a dwarf planet that is farther out in space than the planet Neptune. The three known plutoids are Pluto, Eris and Makemake (MAH-kee-MAH-kee). Astronomers use telescopes to discover new objects like plutoids.

 Try This!!! 

1. __________ is the smallest planet in our Solar System and also the closest to the sun.

2. NASA’s MESSENGER spacecraft is currently orbiting the Mercury. What is the full form of MESSENGER?

3. Phobos and Deimos are moons of ______.

4. __________ is the largest planet in our Solar System and spins very rapidly (10 Earth hours)

5.  Which planet is best known for its prominent ring system?

6. The only spacecraft to ever visit Neptune was ___________.

7. In 2006, NASA launched the first mission to Pluto. It is called __________.

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