The Solar System may appear calm and well organized, but it is actually the result of billions of years of delicate cosmic balancing. Changing the order of the planets might sound like a fun ...

The planets in order of size, listed from biggest to smallest: Jupiter: 43,441-mile radius Saturn: 36,184-mile radius Uranus: 15,759-mile radius Neptune: 15,299-mile radius Earth: 3,959-mile radius ...

The trouble with super-Earths If a planet remains relatively small, with a radius less than 1.5 times Earth's radius, then its gravity is not strong enough to hold onto a huge amount of atmosphere, ...

If you were to plot on a graph how many planets of each size astronomers have discovered, you'd find two peaks: one at 1.4 times Earth 's radius, and another at 2.4 times Earth's radius.

The Europeans described the planet they had discovered as Uranus-size -- which is about 14 times the mass of Earth. The smaller the planet, the greater the odds that it is similar to Earth.

Rocky versus gaseous planets In our Solar System, we have two kinds of planets: small, rocky, dense planets that are similar to Earth and large, gaseous planets like Jupiter.

As the planet grows in size, its mass and therefore gravity increases, allowing it to capture not only the accumulated dust and rocks – but also the gas, which forms an atmosphere.