Why is Pluto no longer a planet?
What is it about Pluto that made astronomers – such as the likes of Dr Mike Brown, Professor of Planetary Astronomy at the California Institute of Technology (Caltech) – insist on its declassification?
Asked by Lauren Walsh
According to the International Astronomical Union (IAU), for an object to be classed as a planet, it needs to meet three requirements. Firstly it needs to be in a orbit around the Sun, secondly it should have enough gravity to pull itself into a spherical shape and thirdly it needs to have “cleared the neighbourhood” of its orbit.
Pluto orbits the Sun and it’s also spherical in shape, fitting two requirements. However, the planet gets into trouble when astronomers look into the final rule. Pluto – which we have known as the ninth planet of our Solar System from its discovery in 1930 by American astronomer Clyde Tombaugh up until its declassification to dwarf planet in 2006 – does not clear its neighbourhood. That is, it’s unable to consume smaller bodies or throw them away using its gravity since it’s only 0.07 times the mass of nearby objects.
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