Is Pluto a planet?
Pluto is officially no longer classed as a planet, and here's why. The International Astronomical Union defined three rules in 2005 that a celestial body (an object observable within space) must follow to be classed as a planet:
1. The planet must orbit the sun.
2. The planet must be large enough that its gravity can smooth it into a nice spherical shape.
3. It must have cleared up the surrounding objects around it.
Pluto fails number three as it simply isn't massive enough to pull the surrounding objects into it's orbit. This is really hard for Pluto as it lives in the Kuiper Belt, a belt of other large rocky objects.
Fortunately for Pluto it matches the first two rules, so it can be classed as a dwarf planet instead!
CG
Related Physics A Level answers
All answers ▸Draw the electric field lines produced by a negative point charge and calculate the electric field strength at a distance of 50mm from a point charge of size -30nC.
The electric potential energy of two protons is 1.0MeV. Calculate their separation
The roar of a tiger in a zoo can be heard by visitors at the entrance, even though the tiger can not be seen because there is a hill in the way. Name and explain this effect.
A small ball of mass 150 g is placed at a height of 20cm above the ground on an incline of 35°. It is released and allowed to roll down the slope; what will be the ball's speed when it reaches the ground? Assume friction and air resistance can be ignored.