The Strangest Planet

Why isn't Pluto a planet anymore? When we ask a question of what is and isn't a planet, we are really just talking about how we define the word 'Planet'. In ancient times, humans didn't really need a definition. Astronomers know 5 star like objects, Mercury, Venus, Mars, Jupiter and Saturn. They didn't really move around like the other stars, they just thought it just wondered through the sky. The word planet comes from an ancient Greek word that meant 'Wonderer'. Eventually astronomers found out that Earth is a planet too, orbiting around the Sun just like the others. Thats pretty much it for the Solar System until the age of Telescopes.

The next planet to be discovered it Uranus in 1781 followed by Neptune in 1846. These planets are huge but not as huge as Jupiter and Saturn. They are just too far away for ancient astronomers to see. In 1801, an astronomer discovered another planet, or so he thought. The astronomer found a spherical object about 600 miles across in between Mars and Jupiter. The planet which is smaller than our moon is called Ceres. In this case, it was not too distant to see but just too small. The problem however is that Ceres had so called 'buddies', lots of them. The next year a slightly smaller object was discovered called Pallas and two years after that another one named Juno. Now they know about thousands of these similar rocky planets. Instead of adding thousands of planets into our Solar System, astronomers decided it makes more sense to group these objects together and named them Asteroids and thats how we have the Asteroid Belt between Mars and Jupiter.

Now we reached to Pluto, which by far to me is the strangest planet. An astronomer discovered Pluto in 1930. But since then, its status as a planet has been called into question. First of all, Pluto's orbit is strange. You can see it on the last picture below. It is outside the Kuiper Belt and even intersecting the orbit of Neptune. Also, it turns out that Pluto is not as big as astronomers really thought. Instead, it has got a huge moon near it and thats why some people call it a binary planet or a double planet. And, just like Ceres, astronomers discovered that Pluto is not alone. Beginning in the early 1990's, they started finding other objects similar to Pluto. Some like Quaoar and Sedna are almost as big. Then in 2005, astronomers announced that they found an object named Eris, even bigger than Pluto.

So, are all these planets? Astronomers wondered the same thing. In August 2006, astronomers from all over the world met and finally decided on a formal definition of a planet. Pluto and its so called 'buddies' did not make the cut and now they are known as Dwarf Planets. So this is why Pluto is the strangest planet to me, it is the only planet in history to be knows as both a planet and a dwarf planet in the solar system.