Yes, Pluto is no longer a planet within the solar system.
What is Pluto? No, – am not talking about the Disney character. And a planet by that name does not exist. Well, at least not anymore!
When Pluto (this name was suggested by an eleven year old school girl in Oxford. It means the Roman God of the underworld) was discovered in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona little did he know that this would be the outcome of his discovery – the planet would lose its “planet” status.
Pluto’s mass came to be known only after the discovery of its largest Moon, Charon, in 1978. Its mass is 0.0021 the Earth’s and is 1,500 miles across! Astronomically this size is considered tiny. And yet this was the largest outside Neptune’s orbit.
The problem began when more such icy objects, like Pluto, was discovered in what was termed as the Kuiper Belt. This belt extends from the orbit of Neptune to 55 times the distance of the Earth to the Sun. The final bombshell was dropped in 2005 when Eris was discovered. It had 25% more mass than Pluto!
Astronomers finally decided to call Pluto a “dwarf planet” in 2006 at the XXVIth General Assembly of the International Astronomical Union. According to them, it met 2 of the 3 criteria that had to be met to be called a planet.
1.It needs to be in orbit around the Sun – YES
2. It needs to have enough gravitational pull so that it can pull itself into a spherical shape – YES
3. It needs to have “cleared the neighborhood” of its orbit – NO
For the new generation to learn what we learnt at school – ie, “the solar system has nine planets”, Pluto will have to crash into many smaller icy objects in the Belt and gain mass in order to satisfy the third criterion.