Imaging Jupiter at Close Range
29 Mar 2001
(Source: Royal Astronomy Society)
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IMAGING A GIANT AT CLOSE RANGE
Just before 2001 dawned, NASA's Cassini spacecraft hurtled past Jupiter, the largest planet in the Solar System, sending back stunning images of the gas giant's turbulent atmosphere, exotic moons and faint rings.
On Wednesday 4 April, during the UK National Astronomy Meeting in Cambridge, Professor Carl Murray (Astronomy Unit, Queen Mary, University of London) will highlight new discoveries revealed in the tens of thousands of images sent back by Cassini.
Professor Murray is a member of the Imaging Science Subsystem (ISS) team that designed and operates the two cameras on board the Cassini spacecraft. He has been involved in the project since its inception in 1990 and for him there was a personal satisfaction in seeing the cameras working so flawlessly.
"This was our first real chance to see the cameras operating under the sort of demanding conditions we might expect at Saturn and they did not let us down," he says.
To date Cassini has returned almost 30,000 images taken by the two cameras on the spacecraft. All the images were calibrated using software written by the Queen Mary group.
VOLCANIC ERUPTIONS, MOONS AND RINGS
Cassini's passage through the Jovian system was fairly distant, coming no closer than 9.7 million kilometres (about 6 million miles). However, the flyby provided an ideal vantage point from which to view Jupiter's colourful cloud tops and turbulent atmosphere.
The spacecraft's cameras were programmed to take sufficient numbers of images so that movies could be made to show the atmosphere's complex dynamical behaviour. (Although NASA's Galileo spacecraft is already orbiting the planet, the failure of its high-gain antenna to open properly meant that data-intensive activities such as the movie sequences could not be accomplished.)
Cassini has now made up for Galileo's shortcomings. As well as making movies the Cassini cameras have obtained images of lightning associated with storms in Jupiter's atmosphere and detected the first dark-side images of aurorae near Jupiter's south pole.
Professor Murray's main interest is in planetary rings and their associated moons. Jupiter has at least 28 moons but 20 of these orbit in elongated paths at distances of more than 100 Jupiter radii (1 Jupiter radius = 71,398 km) from the planet.
On 19 December 2000 Cassini passed within 4.4 million kilometres of Himalia, the largest of these outer moons. The images showed an irregular shaped body that is thought to be a captured asteroid. These will be useful in determining the origin of this unusual class of moons.
Jupiter also has four small moons orbiting close to the planet and two of these, Metis and Adrastea, are thought to be the source bodies for the planet's dusty ring. During a 40 hour sequence, Cassini's cameras were able to focus on these moons and the dusky, dark ring, even though it is almost 100,000 times fainter than Jupiter. The Queen Mary group is analysing these images to provide improved orbits for the moons and to understand better their dynamical connection with the ring.
Perhaps the most dramatic images of all were Cassini's views of volcanic eruptions on the large, pizza-like moon Io. Although Cassini's distant flyby meant that it could not match the high resolution images of Jupiter's large moons seen up-close by the Galileo spacecraft, it was able to capture two enormous, erupting plumes on Io, the most volcanically active body in the Solar System.
The plumes are almost 400 kilometres (about 250 miles) high and emanate from two volcanoes known as Pele and Tvashtar. Images of Io returned by the Galileo spacecraft in March show that a giant red ring of material has been deposited around each volcano as a result of the eruptions.
"Having seen how well the cameras and the spacecraft performed at Jupiter, I am confident that Cassini will continue to provide a wealth of new scientific discoveries and stunning images when we reach Saturn in 2004," says Professor Murray. "The best is yet to come."
Launched in October 1997 the Cassini spacecraft is a key part of the international Cassini-Huygens mission to the planet Saturn in 2004. The mission is a collaboration between NASA, ESA and the Italian space agency.
Cassini will carry out the most detailed study yet of the Saturn system. It will also deliver the European-built Huygens probe to the surface of Saturn's largest moon, Titan, a planet-sized world that is thought to have an atmosphere similar to that of a primitive, pre-life Earth.
The spacecraft has followed a tortuous route through the inner Solar System, picking up gravitational energy from Venus (twice) and Earth before receiving its final "kick" from Jupiter last December. Having received its final helping hand from Jupiter, Cassini is now on its way to a rendezvous with Saturn in July 2004 and the start of a four-year tour of the Saturnian system.
The ISS team is led by Professor Carolyn Porco of the University of Arizona. UK participation in Cassini and Huygens is funded by the Particle Physics and Astronomy Research Council.
Prof. Carl Murray
Queen Mary, University of London
Mile End Road
London E1 4NS
Phone: +44 (0)207-882-5456
Fax: +44 (0)208-983-3522
IMAGES AND MOVIES:
Images and movies from the ISS cameras can be obtained from the Cassini Imaging Central Laboratory for Operations (CICLOPS) at:
RELATED WEB SITES: http://www.jpl.nasa.gov/cassini/