Missions, Science

& Discoveries

Cassini at Saturn: An Overview

• Reached Saturn on 1 July 2004

• Voyage of 2.2 billion miles

• Entered at 149,000 mph

• 96-minute reverse engine burn to

slow the craft to orbit speed

• Passed through the ring system.

Closest it will ever be to the rings.

• Orbits Saturn every 19 days

• Instrumentation in ‘record’ mode

15 hours per day

• Data transmission including up to

500 images per day

MISSIONS

• Primary Mission

• June 2004 – June 2008

• Objectives: 27 diverse science investigations of the Saturnian System

• 1st Extended Mission “Cassini Equinox”

• July 2008 – September 2010

• Objectives: System Tour & Saturnian Moon fly-bys

• 2nd Extended Mission “Cassini Solstice”

• October 2010 – September 2017

• Objectives: Titan, Enceladus, Ring System & Magnetic Environment

CURRENT HEALTH STATUS - JUNE 2012

Optical Remote Sensing InstrumentsComposite Infrared Spectrometer (CIRS) Operational

Imaging Science Subsystem (ISS) Operational

Ultraviolet Imaging Spectrograph (UVIS) Operational

Visible and Infrared Mapping Spectrometer (VIMS) Operational

Fields, Particles & Waves Instruments Cassini Plasma Spectrometer (CAPS) Operational

Cosmic Dust Analyzer (CDA) Operational

Ion & Neutral Mass Spectrometer (INMS) Operational

Magnetometer (MAG) Operational

Magnetospheric Imaging Instrument (MIMI) Operational

Radio & Plasma Wave Science (RPWS) Operational

Microwave Remote Sensing Instruments Radar Operational

Radio Science (RSS) Issue

VERDICT…

Cassini is in Excellent Health !!!

• Early June 2004 – Phoebe ‘enroute’

flyby

• 137 miles across

• 4 times more distant than any other

Saturnian moon

• Cassini added more knowledge about

Phoebe than had been accumulated

in the 100 years since the moon was

discovered

• Phoebe is lighter than rock but

heavier than ice, similar to Neptune

and its moon Triton

• Dark surface contains water

ice, carbon dioxide and primitive

organic chemicals

PRIMARY MISSION – THE BEGINNING

PRIMARY & EXTENDED MISSION OBJECTIVES

27 Science Investigations aimed at answering…

• What is the source of heat inside Saturn?

• What is the origin of Saturn’s rings?

• Where do the subtle colours in the rings come from?

• Are there any more moons?

• Why does Enceladus have such an abnormally smooth surface?

• What is the origin of the dark organic material covering one side of the moon Iapetus?

• Which chemical reactions are occurring in Titan’s atmosphere?

• What is the source of methane in Titan’s atmosphere?

• Are there oceans on Titan?

• Do more complex organic compounds and ‘pre-biotic’ molecules exist on Titan?

• Huygens separated from Cassini on 24 December 2004

• Descent to Titan’s surface on 14 January 2005

• Recorded a wealth of atmospheric data during descent

• Returned 350 images to Earth via Cassini

• Survived on Titan’s surface for 90 minutes before its power died

THE HUYGENS PROBE

VIDEO PLACEHOLDER

TITAN DISCOVERIES

• NO extensive liquid oceans. Instead, liquid hydrocarbon lakes discovered at polar regions

• Evidence for methane drizzle and seasonal hydrocarbon rainfall

• Geologically young surface. Earth-like processes at work including weathering and erosion

to keep surface relatively free of impact craters

• Possible plate tectonics. Cassini observed systematic shifting of surface features over 30km

distance between 2005 and 2007

• Patterns of air circulation from west to east. One large Hadley Cell with north -south high

altitude transfer.

• Super-rotator. Atmosphere rotates more quickly than the surface (like Venus)

• Possible subsurface ocean (water / ammonia mix) detected via ELF radio waves.

• Evidence of negative ions with roughly 10,000 times the mass of hydrogen in Titan's

ionosphere. Assumed to be Tholins – complex organic molecules formed by UV interaction

with simpler organic molecules. Precusors for life. Tholins sink through Titan’s atmosphere

to give red / orange hue.

• Methane source? Undecided…Could be release from within Titan itself via cryovolcanism or

from biotic environment…

FAST FACTS…

• 318 miles wide

• Covered in water ice

= highly reflective

surface

• One of the brightest

objects in the solar

system

• Why is Enceladus of

interest to Cassini

scientists?

ENCELADUS

• Discovered November 2005

• Active eruptions of water ice extending 314 miles above the surface

• Thought to come from pressurised subsurface liquid water reservoir with temperature of +0c

• Internal heat source –unknown

• Extent of geological activity –unknown

• Complex organic chemicals found within the jet material

• Astrobiological potential from an environment where there is no sunlight or oxygen?

• Investigations ongoing…

ENCELADUS JETS DISCOVERY

• Icy particles from Enceladus

feeding material into Ring E

• Fine scale gravitational

instabilities

• New ringlets

• A new moon – Prometheus -

‘stealing’ particles from the F

ring

SATURN’S RINGS

Prometheus

– the Moon

Prometheus –

Ridley Scott’s

spacecraft

• Monstrous polar vortices as heat

wells up from Saturn’s interior

• Powerful giant polar

thunderstorms – 10,000 times

more powerful than on Earth

• Extensive polar aurora displays

lasting several days at a time

• Wind rates are changeable

around the equator

THE FORECAST ON SATURN…

• In 1997 – 18 Saturnian moons

• By 2004 – 13 more discovered by ground observations

• Cassini Era: An additional 31 Saturnian moons discovered for a total of

62

• To date, 52 have been named

NEW MOON DISCOVERIES

• Potential ring system?

• Tenuous – yet to be imaged

• Evidence…impacts from

deorbiting material

RHEA

• Thick icy surface behaves like rock

• Fault lines suggesting active ice

geology

• Light & Dark Hemispheres are

‘active’

• Slow rotation – 1 day is longer

than 79 days on Earth

• Dark material exposed by

sublimation of surface ice from

solar heating

• Thermal segregation redeposits

ice at the colder limbs

• Source of dark material -

unknown

IAPETUS

• Ice fractures forming cliffs and

canyons

• Cliffs several hundred metres

high

• Subsidence cracking

• Suggestive of past tectonic

activity

DIONE

• Sponge-like surface

• Deep and extensive cratering

• Minimal surface ejecta

• Slumping and landslides inside

many deep craters

• Bright crater walls suggest

abundance of water ice

• Complex compounds discovered

including frozen carbon dioxide,

frozen methane and other

hydrocarbons

HYPERION

• Cassini set to be active until September 2017

• Watch this space for discoveries !!

SOLSTICE MISSION