1. A planet must be round in shape. What this means is that is planet must be large enough to have had its mass pulled into a round shape as the result of its own gravitational forces. It was also suggested, but not made part of the definition, that a planet must be at least 1000 kilometers in diameter.

2. Planets must have a defined, regular orbit around the Sun, and not be either stars themselves or satellites of other planets.

3. To be a planet a space object must dominate its own orbit and clear its own area of other smaller space objects.

A "dwarf planet" was defined as a celestial body that is in an orbit around the Sun, has sufficient mass for its own gravitational forces to assume a hydrostatic equilibrium or "nearly round" shape, has not cleared its orbital neighborhood of other space objects, and it is not a satellite.

The IAU also resolved that all other space objects, except satellites orbiting the Sun, shall be referred to collectively as "Small Solar-System Bodies"

The old mnemonic “My very energetic mother just served us nine pizzas”, by which millions of people learned to recite the planets, no longer applies. However, We do have a new one to help you remember the planets in the new line up.

“My very Energetic Mother Just Served Us Noodles.”

Here are some other, more original suggestions:

“My very exhausted mother just sent us nachos”