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Why Pluto is no longer a planet?

 

Pluto is an icy dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered.

 

Clyde Tombaugh discovered Pluto in 1930. Pluto is a tiny ball of ice and rock. It has an elliptical orbit at an angle of 17 degrees. It is only 459th size of planet earth making it smaller than the moon.

 

At its warmest, when it is closest to the sun, Pluto can reach temperatures of minus 369 degrees Fahrenheit (minus 223 degrees Celsius). At its coolest, temperatures can fall to minus 387 degrees F (minus 233 C).

 

Pluto takes 248 Earth years to make one revolution around the sun. That means one year on Pluto is about 248 Earth years. Pluto rotates much more slowly than Earth so a day on Pluto is much longer than a day on Earth. A day on Pluto is 6.4 Earth days or 153.3 hours long.

 

NASA's New Horizons was launched on January 19, 2006 and it became the first spacecraft to visit dwarf planet Pluto in July 2015. 

26th General Assembly of the International Astronomical Union (IAU) was held at Prague in August 2006. IAU redefined the definition of what is a planet and what not is a planet.

 

So, the three criteria of the IAU for a full-sized planet are:

 

• It is in orbit around the Sun.

• It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).

• It has “cleared the neighborhood” around its orbit.

 

Essentially Pluto meets all the criteria except one —it “has not cleared its neighboring region of other objects.” The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet.

 

So any large body that does not meet these criteria is now categorized as a “dwarf planet".