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Last Updated: Thursday, 1 July 2004, 12:57 GMT 13:57 UK
Cassini sends close-ups of rings
Nasa/JPL/Space Science Institute

The international mission to Saturn - Cassini-Huygens - has returned the first close-up images of Saturn's rings.

The probe successfully entered an orbit of the sixth planet on Thursday.

The $3.3bn probe fired its main engine for 95 minutes to slow it sufficiently to be captured by the gravity of Saturn and begin its four-year science mission.

"That brings tears to my eyes. That's just gorgeous," said Cassini's imaging team leader Carolyn Porco on seeing the remarkable first pictures of the rings.

This isn't science fiction, we actually did this
Ed Weiler, Nasa associate administrator

Many of the images show ripple-like features in the rings called density waves which arise from differences in the packing of ring particles.

The pictures also show a phenomenon known as a bending wave - a spiral warping effect in the ring plane.

Both types of wave feature are caused by the influence of Saturn's external moons on the ring system.

Ed Weiler, the US space agency's associate administrator, said the pictures and other data would tell scientists more about how ring systems form around planets and stars.

"This isn't science fiction, we actually did this," he told reporters in Pasadena, California.

Images taken during Thursday night's pass through and over the ring system also show Pan, Saturn's elusive innermost moon, which orbits the planet in the Encke gap - a narrow space in Saturn's A-ring.

Dr Porco added that scientists could not tell anything yet about the composition of the rings. But differences in colour in the latest pictures, most of which were taken using the narrow-angle camera aboard Cassini, might be indicative of differences in the material that makes up the rings.

'Shock' surprise

Mission scientists have also unveiled an initial map of Saturn's magnetosphere from measurements taken by Cassini's Magnetospheric Imaging Instrument (Mimi).

The map shows that radiation from the magnetosphere extends from between 1,130,000km (700,000 miles) and 1,600,000km (one million miles) into space.

On Sunday, Cassini encountered Saturn's "bow shock", the region where the solar wind and Saturn's huge magnetic "bubble" meet. Over the next few weeks, Mimi scientists will build up a movie from maps of Saturn's magnetosphere to show its dynamics.

1. Antennas enabling communication with Earth
2. Boom carrying instrument to measure magnetic fields
3. Two cameras will take 300,000 pictures of the planet
4. Infra-red spectrometer analyses Saturn's temperature and composition
5. Radioisotope thermoelectric generators supply 750W of power
6. Cassini has two engines - one is a back-up
7. Thrusters used for small changes of direction or speed
8. Huygens probe will land on Saturn's largest moon, Titan
9. Plasma spectrometer measures charged particles and solar winds

"We saw the bow shock at about 49 Saturn radii and most of us were surprised it happened that soon. In fact, we think the bow shock came out to meet Cassini," said mission scientist William Kurth.

There were cheers and clapping in the mission control at the US space agency's Jet Propulsion Laboratory in California when confirmation came through that Cassini was in its correct orbit early on Thursday.

The joint US-European mission has travelled for more than six years and covered over three billion km to get to the ringed planet.

Tracking data revealed the long burn came to an end just a minute earlier than expected.

Ground controllers may still have to perform a so-called clean-up manoeuvre to adjust the probe's orbit around Saturn, which is estimated to be about 116.3 days. The original target set by the Cassini team was 117.4 days.

Cassini-Huygens - the main spacecraft carries the Huygens probe intended for delivery to Saturn's biggest moon, Titan - is the first human-made object to orbit around the ringed planet.

Scientists hope the mission will provide important clues about how the planets formed.

Nasa/JPL/Space Science Institute
The "density waves" are much like ripples in water (Nasa/JPL/Space Science Institute)
They want to learn more about what Saturn is made of - its atmosphere, whipped by ferocious storms; its molten core; and its mysterious rings, thought to be the remains of shattered comets, asteroids and moons.

Cassini's instruments measure magnetic fields and radio waves, charged particles, cosmic dust, infrared and ultraviolet light. There are also wide-angle and narrow-angle cameras.

In December, the spacecraft will release Huygens on to Titan, the only moon in the Solar System with a thick atmosphere.

Cassini is set to fly past Titan about 36 hours after orbit insertion, giving scientists a better view of this little-known world before Huygens is despatched.

The Cassini-Huygens mission is a cooperative venture of the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency.

The BBC's Fergus Walsh
"This has been an epic journey across our Solar System"


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