Why is Pluto no longer a planet?

When Mum and Daddy were kids, they were taught at school that there were nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus and Pluto.

But no when we learn about the planets at school we are told there are only 8 as Pluto is no longer classed as a planet! But why isn't it classed as a planet?

The answer is that in August 2006 the International Astronomical Union downgraded Pluto to the status of a "dwarf planet". The reason was because Pluto didn't meet one of its criteria to be classed as a planet. The three criteria to be a planet are:

  1. It is in orbit around the Sun.
  2. It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
  3. It has “cleared the neighborhood” around its orbit.
Pluto didn't meet the third criteria - it "has not cleared its neighbouring region of other objects"

Are there any other dwarf planets?

So now Pluto isn't allowed to play with the bigger planets is it all on its own? The answer is no as there are four other dwarf planets to keep Pluto company. They are Eris, Haumea, Makemake and Ceres.

Fun facts about Pluto!

Pluto is named after the Roman god of the underworld.


Pluto was discovered on February 18th, 1930 by the Lowell Observatory.


Pluto has five known moons; the moons are Charon,Hydra,Nix, Kerberos and Styx.


Pluto is the largest dwarf planet


Pluto is one third water


Pluto is smaller than a number of moons 


Pluto has been visited by one space craft


Pluto’s location was predicted by Percival Lowell in 1915.


Pluto is closer to the sun than neptune for about 8% of its orbit


If you lived on Pluto, you'd have to live 248 Earth years to celebrate your first birthday in Pluto-years.


If you weigh 100 pounds on Earth, you would weigh only 7 pounds on Pluto!


And finally...


Pluto orbits the sun on its side like this:




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