Jupiter

KING of the SOLAR SYSTEM

Named after the King of the Gods, Jupiter is the largest planet in the solar system – it is big enough to swallow all the other planets with room to spare. The first of the gas giants, this stately world is usually the third brightest object in the night sky.

Almost as soon as the telescope was invented, astronomers realised there was something different about Jupiter  – for one thing it had a slightly oval appearance, and for another, its most prominent features were dark and light bands across its surface. 

Dutch observer Christiaan Huygens published the first drawing of these bands in 1659, and a few years later the great Italian astronomer Cassini discovered what seemed to be a permanent storm on the surface of the planet. Jupiter’s bulge happened to match Sir Isaac Newton’s predictions on the appearance of a liquid planet and throughout the 18th century astronomers gradually came to realise that Jupiter was in fact cloaked in a deep and impenetrable atmosphere.

FAST SPINNING GIANT

Today, we know that Jupiter is an enormous ball of hydrogen and helium in both gas and liquid form, mixed with traces of some other colourful chemicals that create the vibrant upper cloud layers. At its centre there may be a solid rocky core about the size of Earth, but scientists are far from certain about this (see How It Works: Inside Jupiter). 

The planet spins on its axis once in just under 10 hours, giving it the shortest day and night of any planet in the solar system. The combination of rapid spin and gassy composition gives Jupiter’s equator a pronounced outward bulge – the diameter across the equator is 9000km more than the diameter from pole to pole. 

This rapid rotation is also responsible for Jupiter’s banded weather systems, creating high-speed jet streams that run in opposite directions, wrapping their clouds all the way around the planet parallel to the equator. Different colours of cloud form at different heights and temperatures where varying chemical vapours condense out of the atmosphere. 

High-altitude clouds have lighter colours and 

are called zones. Between the zones run parallel trenches or clearings called belts, which reveal darker-coloured clouds at deeper levels. In areas of unusually high pressure such as the famous Great Red Spot, bright red clouds can form at very high altitudes – see the next issue for more on Jupiter’s weather.