© N

ASA

/JPL

/Sp

ace

Scie

nce

Inst

itu

te

Exploring Saturn

Cassini Huygens is an international collaboration between NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI) to explore Saturn and its largest moon, Titan.

Cassini arrived at Saturn on 1st July 2004. Saturn is a gas giant, composed mainly of hydrogen and helium. With its famous ring system, a plethora of moons and one of the most complex magnetospheres in the Solar System, Saturn is a fascinating target.

What is

? Cassini Huygens Cassini

Huygens

The mission is made up of the Cassini spacecraft, which is in orbit around Saturn, and ESA’s Huygens probe, which landed on Titan. It was launched in October 1997.

The mission is named after two 17th Century astronomers: Jean Dominique Cassini, the discoverer of four of Saturn’s moons, and

Christiaan Huygens, who discovered Titan and realised that the “ears” Galileo had observed

either side of Saturn were actually rings.

UK involvement in Cassini

Imperial College London leads the team behind Cassini's MAG instrument, which is monitoring Saturn's magnetic field. British scientists are also involved in

Cassini's cameras and experiments to monitor Saturn's and Titan’s atmospheres, plasma environment and dust in the Saturnian system. They also carried out

extensive theoretical modelling work to support the mission science.

UK involvement in Huygens

The UK’s Open University, supported by the Rutherford Appleton Laboratory, built the Surface Science Package, which consisted of nine instruments to measure the properties of Titan’s surface after landing. The Open University also provided the high sensitivity accelerometers which enabled the high altitude properties of the

atmosphere to be measured with great precision.

Cassini Huygens launch

Cassini spacecraft

© N

ASA

/Ken

ned

y Sp

ace

Cen

ter

© C

ou

rtes

y N

ASA

/JPL

-Cal

tech

Christian Huygens

© S

mit

hso

nia

n In

stit

uti

on

Li

bra

ries

, Was

hin

gto

n, D

C

Jean Dominique Cassini

• Low-Gain Antenna (1of 2)

• Radar Bay

• Fields and Particles Pallet

• Hygens Titan Probe

• Radioisotope Thermoelectric

Generator (1 of 3)

Remote Sensing Pallet •

• Radio/Plasma Wave Subsystem Antenna (1 of 3)

11m Magnetometer Boom •

High Gain Antenna •

445 N Engines •

The initial four-year mission follows a complex orbital path, allowing the spacecraft to view the planet and its surroundings from different distances and angles. Highlights have been close flybys of many of Saturn’s moons, producing spectacular pictures, and a wealth of discoveries, including new rings, additional moons, a radiation belt, massive mountains and probable lakes of methane and ethane on Titan and ice geysers on Enceladus. An extension to the mission is currently being planned.

Phoebe© NASA/JPL/Space Science Institute

© NASA/JPL/Space Science Institute

© N

ASA

/JPL

/Sp

ace

Scie

nce

Inst

itu

te

Titan

Portrait of Saturn by Cassini

© NASA/JPL/Space Science Institute

Saturn’s Rings

On 14th January 2005, the Huygens probe descended through Titan’s atmosphere to discover what lay beneath the opaque, orange haze. It revealed a landscape that was both familiar and alien. Low-lying hills formed from water-ice bedrock were patterned with river channels and lake beds possibly carved by liquid methane rain. Huygens landed on an undulating surface covered with ice pebbles.

Data from the impact suggests that the probe bounced off a pebble before

settling on a surface that reacted like lightly packed snow or damp sand.

Huygens did not detect standing or running liquid, but it found the atmosphere

at the surface, and probably the surface itself, was ‘moist’ with liquid methane.

During the descent, which lasted 2 hours and 28 minutes, the probe measured the physical and chemical properties of Titan’s atmosphere. It confirmed that nitrogen and methane were the most common gases and that, unexpectedly, the methane “haze” was present right down to the surface. An isotope of argon was detected at the surface, which together with the high concentrations of methane, suggests that Titan has ongoing volcanism.

Above left: Artist’s impression of Huygen Probe

Above: Titan’s surface

Right: Colour view of Titan’s surface

Left: Mosaic of river channels Images © ESA/NASA/JPL/University of Arizona

Cassini arrived at Saturn on 1st July 2004. Saturn is a gas giant, Cassini arrived at Saturn on 1st July 2004. Saturn is a gas giant, composed mainly of hydrogen and helium. With its famous composed mainly of hydrogen and helium. With its famous ring system, a plethora of moons and one of the most complex ring system, a plethora of moons and one of the most complex magnetospheres in the Solar System, Saturn is a fascinating target. magnetospheres in the Solar System, Saturn is a fascinating target.

Further InformationIf you would like to know more about the Cassini Huygens mission, try the following resources:

World Wide Web sites

saturn.jpl.nasa.gov

sci.esa.int - missions - Cassini Huygens

www.uk2planets.org.uk

www.nineplanets.org

Books

Ralph Lorenz & Jaqueline Mitton

Lifting Titan’s Veil

Cambridge University Press, 2002

David M Harland

Mission to Saturn: Cassini and the Huygens Probe

Springer Praxis, 2002

Fredric W. Taylor

The Cambridge Photographic Guide

to the Planets

Cambridge University Press, 2001

Cover image: Saturn Approach

by Cassini

The Science and Technology Facilities Council operates world-class, large-scale research facilities; supports scientists and engineers world-wide; funds researchers in universities and provides strategic scientific advice to government.

The Council’s Science in Society unit offers a wide range of support for teachers, scientists and communicators to facilitate greater engagement with STFC science which includes astronomy, space science, particle physics and nuclear physics:

For Schools

• Free Publications and resource guides suitable for teaching ages 10-18. Go to www.scitech.ac.uk - Public and Schools - Schools and Education - Resources

• Funding schemes for projects and school visits. Go to www.scitech.ac.uk - Public and Schools - Funding

• A Moon rock and meteorite loan scheme. Go to www.scitech.ac.uk - Public and Schools - Schools and Education - Loan Scheme

• Visits to STFC’s UK laboratories in Cheshire, Oxfordshire and Edinburgh plus CERN in Geneva. Go to www.scitech.ac.uk - Public and Schools - Visits and Events

• Researchers in Residence. Teachers are placed in partnership with young scientists who have been trained to support the teacher, act as role models and introduce their research. Go to www.researchersinresidence.ac.uk.

For Scientists

• Communication and media training courses; funding schemes and Fellowships for public engagement. Go to www.scitech.ac.uk - Public and Schools - Fellowships and Communications Training

For further information telephone 01793 442175 or email gareth.james@stfc.ac.uk

are made of water ice crystals. The colour variation is caused by contamination from rock or carbon compounds.

© NASA/JPL/Space Science Institute

Saturn’s rings

Comparisons with data collected by NASA’s Voyager spacecraft in the early 1980s show that Saturn is a dynamic, changing planet. The planet’s northern hemisphere is bluer than in the Voyager images, probably because shadows cast by the rings have caused the atmosphere to cool so the yellowish, sulphur-rich clouds have sunk out of sight. Wind speeds at the equator also appear to have slowed down. Cassini has been able to peer down into the lower atmosphere and see turbulent, localised weather patterns.

At first, Cassini observed none of the radial “spoke” features in the rings that were seen abundantly by Voyager 1&2 and thought to be caused by electrically charged dust particles above the ring. The incidence of spokes appears to be linked to changes in Saturn’s magnetic field and the angle of the rings in relation to the Sun. As Cassini watches Saturn through its seasons, it should start to see the spokes more frequently.

Cassini has used detailed observations of Saturn’s magnetic field to measure accurately the length of a day on Saturn and found it to be 10 hours and 47 minutes. As Saturn’s magnetic and rotational axis are almost perfectly aligned and there are no fixed features to monitor in the atmosphere, previous estimates have varied by several minutes.

Cassini has also carried out the first detailed study of Saturn’s magnetosphere, finding that it extends much further towards the Sun than expected. It has also discovered a radiation belt of electrically charged particles trapped inside Saturn’s innermost ring, the D-ring, and found that the rings themselves have an “atmosphere” of gases and charged particles on the sunlit side.

Titan has been revealed to be a complex world with icy continents, cryogenic volcanoes and, probably, lakes of liquid methane. Observations of Enceladus have shown plumes of water vapour streaming out from vast cracks, dubbed “tiger stripes”, near the south pole. The processes that cause these geysers are a mystery, but they could indicate liquid water beneath the surface of Enceladus. The material vented is a source of Saturn’s diffuse E-ring.

Cassini has discovered several new moons, including one embedded within a gap in the rings. Cassini images have also helped improve understanding of the interactions between the icy particles that make up the rings and the “shepherd” moons that orbit around them.

Scientists around the world will now spend several years analysing the data from Cassini and Huygens to develop a greater insight into this extraordinary part of our Solar System.

PhoebeHyperionRheaDioneTethys

Enceladus

IapetusHeleneCalypso

MimasPrometheusPanJanus

EpimetheusPandoraAtlas

Telesto Titan

has one hemisphere covered with a dark material of an unknown origin.

A ridge that runs along the equator is in places 12 km wide and 13 km high.

is surrounded by Moons. Cassini has

studied many of them and discovered more.

Its surface is covered with impact craters and has a

spongy appearance due to thermal erosion. © NASA/JPL/Space Science Institute

has relatively few impact craters in its southern

hemisphere, indicating a geologically young surface. The plumes of water ice originate from the long, parallel fractures.

This image taken by Cassini’s VIMS instrument, using infra-red light, shows the pattern of dark

and bright features that cover the surface of Titan. © University of Arizona/LPL

Hyperion

TitanEnceladus

Saturn

The 18 largest of Saturn’s many moons