Why Pluto Lost Its Status as a Planet

We all went to school and learned that there were nine planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, and it is very rare before scientific facts get changed.

However, this fact did change in 2006, when the International Astronomical Union (IAU) voted that Pluto be reclassified as a dwarf planet instead of a real one. This implies that only the gas giants, which are Jupiter, Saturn, Uranus, and Neptune, and terrestrial planets like Mercury, Venus, Earth, and Mars will be considered as planets from now on.

Members of the public were surprised and enraged at the same time. Some authors had to rewrite their textbooks to avoid spreading the wrong information.

But the question lingering in the minds of people is this: Why isn’t Pluto a planet anymore?

More About Pluto

The word “planet” is from the Greek word “planetes,” which implies “wandering star.” Mercury, Venus, Mars, Jupiter, and Saturn can be seen with the naked eye and are constantly shifting in bizarre pathways across the sky, just the way more distant background stars do. When the telescopes came into existence, scientists were able to discover Uranus and Neptune, which are too faint to be visible to the human eye.

When, then, was Pluto established as a planet?

Pluto was discovered and classified as a planet in 1930 when Clyde Tombaugh (from the Lowell Observatory) made some comparisons of different photographic plates of the sky on different occasions and noticed that there was a tiny dot that moved to and fro against the star backdrop. At that point, the solar system had a possible new candidate that was odd. It could actually get closer to the sun than Neptune for up to 20 years of its 248 years trip.

In 1992, some scientists discovered 1992 QB1, a very tiny object orbiting around Pluto’s area, and it was the first Kuiper Belt object. Many more objects were discovered with time. Pluto, however, remained the lord of the area until July 2005, when scientists discovered Eris, a distant body that was thought to be way larger than Pluto at first sight.

That’s when scientists began to question their findings. Things they considered included:

  • If Pluto is a planet, does it mean that Eris is one too?
  • What exactly is the basis for classifying a planet as one? A word that sounded so straightforward and simple no longer made sense.  
  • What would we call all those other objects in the Kuiper Belt?

Different controversies and suggestions arose in the Prague Conference, especially when a new definition for the word “planet” was being discovered. One of the controversies suggested that the total number of planets should be up to 12, and this includes Pluto’s moon, Charon, and the largest asteroid, Ceres.

At the end of the day, the astronomers created three new categories for the solar system objects, and this made Mercury to Neptune the only planets that existed. Pluto and its buddies – the objects that shared their orbits with other bodies, were classified as dwarf planets. The other objects that orbit around the sun will now be referred to as solar system bodies.

Why Pluto Lost Its Status as a Planet
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