Jupiter is the largest of the planets in the Solar System. Its mass is about 2.5 times the mass of all the other planets combined. It is also the closest Jovian planet to the Sun. Here is some data about it:
Jupiter's escape velocity probably accounts for the large amount of hydrogen that it has - its escape velocity is 61 km/sec, compared to 11 km/sec of the Earth. Its surface temperature is about 300 degrees Kelvin, however as you go deeper into the planet the temperatures increase very fast. At the start of the metallic hydrogen level, the temperature is about 10,000 degrees Kelvin and the pressure is 3 million atmospheres. At the surface of the central core, the temperature is 25,000 degrees Kelvin and the pressure is 12 million atmospheres.
One interesting feature of Jupiter is the Great Red Spot, a storm system about 3 times the size of the Earth which has persisted for over 350 years. Similar features have not been found on any other Jovian planet in the Solar System.