Images of Jupiter show a bright, massive world, with light and dark parallel bands of clouds. The planet has at least 16 moons and seems a small solar system in itself. Indeed, Jupiter is so huge, with a diameter of 140,000 km, that if it were about 10 times larger, it too would be a star.

     For all its size, Jupiter is barely more dense than water, at 1.33 g/cm3 This low density indicates that Jupiter is composed of very light materials. In fact, Jupiter is mostly made of helium and hydrogen in both liquid and gaseous states. Jupiter's mass 18.99 x 10 27 kg, means that the planet has a high escape velocity, 60km/s and is able to hold onto these light elements.

     It takes the giant planet 11.8 of our years to go once around the Sun, but a day on Jupiter would surprise you. Big as the planet is, it rotates once every 9 hours 56 minutes! Rotating this fast causes the planet to flatten at the poles and bulge at the equator. This bulge is so pronounced that it can be seen in images.