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Wednesday, 9 February, 2000, 19:15 GMT
Jupiter's thunderous rising damp

Thunderstorm Thunderstorm on Jupiter with white water clouds

By BBC News Online science editor Dr David Whitehouse

Astronomers studying the latest images from the Galileo mission believe that the motions of Jupiter's atmosphere are driven by similar processes to those which drive the weather on Earth.

The atmosphere of Jupiter is thick, multi-coloured and layered. Its swirling blanket of gases include hydrogen, helium, nitrogen, methane, ammonia and water vapour.

Jupiter's Red Spot Jupiter's Red Spot
At the cloud tops are ice crystals of ammonia. Between the jet streams, cyclones and anti-cyclones, there are redder and warmer depths visible.

Swirling clouds of light, the equivalent of the Earth's aurorae, ripple above the clouds while lightning streaks between the cloud layers. Water clouds lurk 50 kilometres below the visible surface but below that it gets too hot for them to survive.

The images on this page come from the Galileo mission, which has been in orbit around Jupiter since 1995. The images are analysed in a report in the journal Nature.

Red Spot

Some aspects of Jupiter's weather system are remarkably stable. The Red Spot, a huge oval storm the size of the Earth, has persisted for at least three centuries. What is more, its atmosphere is divided into stable bands.

Scientists, at Cornell University in the US, looked in detail at two large storms close to the Red Spot, which were accompanied by lightning strikes through the cloud layer.

They suggest that a possible driving force behind these storms is moist convection: the rising of water-rich gases, accompanied by condensation and cloud formation.

Convection is the power behind tropical thunderstorms on Earth. But whereas moist convection on Earth is ultimately powered by the heat of the Sun, on Jupiter there is another power source.

The sunlight falling on Jupiter is only about 4% as strong as it is on Earth. However, Jupiter generates about twice as much heat as it absorbs from the Sun. The energy comes from the giant planet's slow contraction, as well as from the separation of gases within the planet. It is this, scientists believe, which could be powering Jupiter's weather systems.

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See also:
08 Dec 99 |  Sci/Tech
Jupiter gave birth to Uranus and Neptune
17 Nov 99 |  Sci/Tech
By Jupiter! Confusion over planet
09 Jun 99 |  Sci/Tech
Dust cloud surrounds Jupiter's moon

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