Jupiter
http://en.wikipedia.org/wiki/Jupiter
Jupiter is the largest planet in the solar system. It is called a gas giant because it is mainly made of gases. The famous Great Red Spot is actually a giant cyclone that circles around Jupiter. Jupiter has over 63 moons orbiting it. The large amount of moons are due to the fact that Jupiter's strong gravitational field attracts asteroids from the Asteroid Belt. Its four largest moons are called Callisto, Ganymede, Io, and Europa. The largest moon in the solar system is Ganymede which is larger than mercury. Jupiter's weight is equivalent to 318 Earth masses.Structure:
http://www.planetsalive.com/image/jupxsec.jpg
The core of Jupiter is solid and made up of materials similar to that of the Earth's, with a diameter of about 24,000 km .
Surrounding this, with a thickness of about 100,000 km , is a mixture of hydrogen and helium. In Jupiter's interior the pressure is so high that the hydrogen and helium acts like metal.
Outside this is a layer of liquid molecules, mainly consists of hydrogen and helium.
The surface we see from earth is actually its atmosphere. The cloudy atmosphere is about 1000 km thick. The temperatures in Jupiter's atmosphere is cold ranging in-between -130°C at the top of the clouds to 30°C near the bottom.