Jupiter

The Theory of how the Planets form is called Accretion. It is the idea that during the process of Nebular Hypothesis all the gas and dust that didn't go into making the sun started to collide and gravitate towards each other. Eventually all this matter sticking together, forms a planet. Accretion is still happening today. In July of 1994 A comet named "Shoemaker-Levy 9" collided with Jupiter.  That day Jupiter grew, just a little. The Accretion Theory isn't completely perfect but, the planet Jupiter supports it. Because Jupiter is 778,369,000km from the sun it was cool enough for ice-forming compounds to condense and form the planet just like the other gas giants in the outer disk.Which looking at all the planets explains their different compositions and temperatures. Another reason for the Accretion theory with Jupiter is that it has a diameter of 142,984 km across, which proves the accretion theory because it shows the abundance of materials farther away from the sun and that more gravity would explain it's size. Jupiter as you can see supports the accretion theory. It's days are 9 hrs and 55 minutes. It takes 11.86 years to orbit the sun. And is primarily composed of Hydrogen and Helium. It was also named after the Greek god Jupiter because of it's great size.

http://www2.jpl.nasa.gov/sl9/
http://www.bobthealien.co.uk/jupiter.htm