The Planets

Episode 1

Different Worlds

50 mins

The planets are nine worlds that seem to have little in common, except that they circle around a single sun and are bound together by its gravity. Shortly after World War II the Soviet astronomer Viktor Safronov picks up the 200 year old idea that the planets were formed from a cloud of dust. Gravitational instability first formed big clumps, which through gravity fused to planets. A huge number of such planets then collided and fused until only the four planets of the inner solar system remained. Mercury, Venus, Earth and Mars bear scars of their creation. The craters on their surfaces are signs of hard collisions with collapsing planets. Outside these four planets are the gas giants Jupiter and Saturn, which became so large that they started sucking in the primordial gases from the original dust cloud, thus swelling to 100 times bigger than Earth. The ice giants Uranus and Neptune are still a mystery. The Kuiper belt outside Neptune consists of thousands of gigantic ice chunks. Pluto is one of those chunks. The Kuiper belt is thought to contain the building blocks for the ice giants.