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.”
BACKGROUND INFORMATION
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.
CONTACT:
Prof. Carl Murray
Astronomy Unit
Queen Mary, University of London
Mile End Road
London E1 4NS
Phone: +44 (0)207-882-5456
Fax: +44 (0)208-983-3522
E-mail: C.D.Murray@qmw.ac.uk
IMAGES AND MOVIES:
Images and movies from the ISS cameras can be obtained from the Cassini
Imaging Central Laboratory for Operations (CICLOPS) at:
http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html
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