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Friday, 6 October, 2000, 11:59 GMT 12:59 UK
Cassini approaches Jupiter
Jupiter Nasa
Jupiter's Great Red Spot looms large for Cassini
By BBC News Online science editor Dr David Whitehouse

The Cassini spacecraft is fast approaching Jupiter where it will use the giant planet's gravity to swing on to its ultimate destination, Saturn.

The spacecraft is steadier than any spacecraft I've ever seen

Dr Carolyn Porco, Cassini researcher
The swing by takes place in December with a 2004 arrival date at Saturn. Once in orbit around the ringed planet, Cassini will drop a tiny probe into the thick atmosphere of Saturn's major moon, Titan.

In the meantime, scientists are making observations and taking measurements of the Jovian environment using the spacecraft's instrumentation.

They have also released a stunning image of Jupiter.

Sharp and clear

The image was taken by Cassini's Imaging Science narrow angle camera through a blue filter on 1 October. At that time, Cassini was 84.1 million kilometres (52.3 million miles) from Jupiter.

Cassini Nasa
Cassini's ultimate destination is Saturn
Scientists say that Cassini data will help them tackle some long-standing mysteries of Jovian meteorology and chemistry.

Researchers can already see that the Great Red Spot on Jupiter contains a dark core of absorbing particles.

"This has been our first opportunity to exercise the Cassini flight and ground systems in a mode very similar to how we expect to operate at Saturn, and I'm extremely pleased with how it is working," said Bob Mitchell, Cassini programme manager at Nasa's Jet Propulsion Laboratory in California.

"The spacecraft is steadier than any spacecraft I've ever seen," said Dr Carolyn Porco, of the University of Arizona, and team leader for the camera on Cassini.

"It's so steady, the images are unexpectedly sharp and clear, even in the longest exposures taken and most challenging spectral regions."

Red and blue

The smallest features that can be seen are 500 km (310 miles) across.

The contrast between bright and dark features in the image is determined by the different light absorbing properties of the particles composing Jupiter's clouds.

We are concerned about communications with the Huygens probe, but the best minds in the business are working on solutions

Dr Jay Bergstralh, Cassini researcher
Ammonia ice particles are white, reflecting all light that falls on them. But some particles are red, and absorb mostly blue light.

But scientists are concerned about a technical problem that may affect Cassini's mission at Saturn. The European Space Agency's (Esa) Huygens probe, which is attached to the Cassini spacecraft, appears to have a fault.

Huygens is to drop from the Cassini spacecraft in late 2004 on to the large moon of Saturn called Titan, as the Cassini orbiter begins an exploration of the ringed planet and its other moons.

Communication problem

The concern, which was identified in early September with tests at Esa's Operations Centre at Darmstadt, Germany, involves the receiver that will pick up signals from the probe as it descends through Titan's atmosphere.

According to tests, the signal sent to Cassini from Huygens will change in frequency because of the Doppler effect as both spacecraft rapidly change position in relation to each other.

But engineers have found that the receiver carried on Cassini will not receive all the data from the Huygens probe.

"Cassini has given us the first tantalising taste of its enormous scientific potential," said Dr Jay Bergstralh, Cassini Program Scientist at Nasa.

"We are, of course, concerned about communications with the Huygens probe, but the best minds in the business are working on solutions," he added.

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See also:

18 Aug 99 | Sci/Tech
Saturn probe swings by Earth
11 Jul 00 | Sci/Tech
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