Structure and Atmosphere
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The structure of Jupiter is very unlike that of the Earth. The visible surface is, in fact, the uppermost layers of clouds of methane and ammonia. The interior of Jupiter is made up of a solid core of material similar to that of the Earth with a diameter of about 24,000 km (13,000 mi). Surrounding this, with a diameter of about 100,000 km (56,000 mi), is a metallic mixture of hydrogen and helium. On the Earth we know these two as gases which at very low temperatures can be liquefied; in Jupiter's interior the pressure is so high that the hydrogen takes up a state in which it behaves like a metal. Outside this metallic hydrogen zone is a shell of liquid molecules, mainly hydrogen and helium, with the cloudy atmosphere, about 1000 km (560 mi) deep, above. The temperatures in Jupiter's atmosphere are very cold ranging from -130°C (-200°F) at the top of the clouds to 30°C (90°F) about 70 km (45 mi) below.
The Jovian atmosphere contains numerous belts and storm systems with wind speeds
up to 400 km/hr (250 mph). Between the dark and light cloud zones, wind shear and
turbulence create great rotating storm systems, best exemplified by the Great Red
Spot. The atmosphere consists of the colourless gases hydrogen and helium, and
trace elements that rise from deep in the atmosphere and provide the colour variations
apparent in photographs.
Through a telescope, Jupiter appears as a creamy white. But if you could travel to this giant planet, you would find a world made of vividly-coloured clouds. But no one gas in Jupiter's atmosphere can account for the planet's reds and browns. There are thought to be different cloud layers. An uppermost layer is composed of ammonia ice crystals. Farther down in the atmosphere, it's thought you'd find liquid water and snow. Different chemical processes in the various layers may be what adds colour to Jupiter's clouds. These reactions are fuelled by the many different energy sources available to the planet. The sunlight reaching Jupiter is only about 1/25 as bright as sunlight reaching Earth. But Jupiter has lightning, great auroras, and even an internal heat of its own. Most scientists now believe that Jupiter has a bulk composition similar to that of the gas and dust cloud of the primitive solar nebula from which the planets and our Sun were formed, with added heavy elements from comets and meteorites. Most significantly, the ratio of the elements that make up 99% of the Jovian atmosphere -- helium and hydrogen -- now closely matches that found in the Sun, suggesting that Jupiter's composition has not changed since the planet formed several billion years ago.
