# Presentation: 467361

## Cassini Mission

- A journey to the Saturn System

## Saturn

- Saturn is the sixth planet from the Sun, orbiting at an average distance of
- 9.54 astronomical units (1429.4 million kilometers or 888 million miles).

- Saturn physical facts:
- Diameter = 120,660 km (75,412 miles) - compare to Earth (12,756 km)
- Mean Distance from Sun = 9.5 au = 888 million miles = 1429 million km
- Mass = 569x1024 kg
- (95 times more massive than Earth)
- Rotation Period = 10 hours and 40 minutes

## Saturn System Facts

- Saturn is the second largest planet in the Solar System.
- There are 30 known satellites of Saturn.
- The largest, Titan, has a thick nitrogen-rich atmosphere.
- Saturn has an extensive magnetosphere.
**Did you know?**
- Saturn emits 79% more energy
- than it receives from the Sun.

## Saturn’s “Road Map”

- The order of the rings and moons, starting with the closest to Saturn, is:
- Saturn				Epimetheus		Titan
- D-Ring				Janus			Hyperion
- C-Ring				G-Ring			Iapetus
- B-Ring				Mimas			Phoebe
- Cassini Division			E-Ring			New Satellites
- A-Ring				Enceladus
- Encke Division			Tethys
- Pan				Telesto
- Atlas				Calypso
- Prometheus			Dione
- Pandora				Helene
- F-Ring				Rhea

## Saturn Compared to Earth-Moon System

- Saturn and ring system diameter = 170,000 km (106,250 miles)
- Ring system here does not include the E-ring.

- If you placed Saturn and the main rings (excluding the diffuse E-Ring)
- between the Earth and the Moon, Saturn would barely fit!

## Saturn’s Atmosphere

- Saturn’s primary atmospheric contents are:
- 	Hydrogen (94%)
- 	Helium (6%)
- In addition, there are traces of ammonia, methane, ethane, phosphine, acetylene,
- methylacetylene, and propane.
**Did you know?**
- What makes those colorful golden bands in
- Saturn’s upper atmosphere?
-        ---Ammonia ice crystals

## Saturn’s Wild Winds

- Saturn has the second fastest measured winds in the Solar System.
- Only Neptune has faster winds.
- Wind speeds at similar latitudes north and south of the equator are nearly
- the same.
- Equatorial Speeds: blow to the East at 500 meters/second (1,100 miles per hour)

**How fast is that?**
- A jet airplane travels at an average speed of
- 550 miles per hour.
- The strongest hurricane (cyclone) winds top out at
- about 220 miles per hour.
- A tsunami travels along the open water at 550 miles
- per hour.
- The speed of sound is 660 miles per hour at 30,000 feet.

## Who was Cassini?

- Cassini originally gained fame by determining the rotation periods of Jupiter
- and Mars. Cassini was a meticulous observer and his dutiful technique allowed
- him to discover 4 of Saturn’s moons -  Iapetus, Rhea, Dione, and Tethys.
- Cassini also discovered the large gap in Saturn’s rings which now bears his name
- (The Cassini Division).

- French Italian Astronomer: Giovanni Domenico Cassini (1625-1712)
- changed his name to Jean Dominique Cassini when he moved to
- Paris.

- Cassini was a member of the Royal Academy of Sciences in Paris, France.

## The Huygens Connection

- Dutch Astronomer Christiaan Huygens (1629-1695)

- Christiaan Huygens discovered Titan and was the first person to understand
- Saturn’s rings.
- Huygens was a member of the Royal Academy of Sciences in Paris, France.
- He was also a leader in the fields of optics and mechanics.
- Christiaan Huygens invented the pendulum clock which was the first accurate
- timekeeping device.

- The atmospheric probe that will go to Titan is named “Huygens.”

## Cassini’s Partners

- Cassini is managed for NASA by the Jet Propulsion Laboratory in Pasadena,
- California. In addition, Cassini is supported by academic and industrial partners
- in 33 US states and 16 European Nations.

- The Huygens Probe is managed
-  by the European Space Agency.

## Cassini Spacecraft

- while the Huygens Probe carries and additional 6 science instruments.

**Spacecraft Orientation:**
- +X-axis = remote sensing pallet
- 	(note that primary remote sensing
- 	boresights view in the
- 	direction of the -Y-axis).
- +Y-axis = Magnetometer Boom
- +Z-axis = main engine assembly
- 	(note that the High Gain Antenna
- 	points in -Z-axis).

## Cassini Spacecraft

- Cassini is a very large spacecraft!
- Total spacecraft mass at launch (including propellant) = 5586 kg (12,220 lbs)
- Propellant mass at launch = 3132 kg (6890 lbs)
- Spacecraft height = 6.87 meters (22.3 feet)
- High Gain Antenna Diameter = 4 meters (13.1 feet)
- Magnetometer Boom Extension = 11 meters (36 feet)
- Data Storage Capacity (on-board) = 4 Gbits
- Electrical power at launch = 875 watts
- Main Engine thrust capability = 445 Newtons (100 pounds of force)
- Number of Science Instruments = 12

## Data Quality Comparison

- and those flown on the Galileo spacecraft.
- Resolution of Voyager Image = 1.3 kilometers (0.8 miles) per pixel
- Resolution of Galileo Image = 74 meters (243 feet)
- per pixel
- (more than 17 times better than Voyager image)
- Cassini’s cameras will provide even better
- resolution than the Galileo cameras.

- The cameras on-board Cassini have a much higher resolution than those
- on the Voyager spacecraft.

## Huygens Probe

- The probe has a heat shield, parachute package, engineering equipment
- including batteries, and six scientific instruments to collect data at Titan.

- Mass = 350 kg (770 lbs)
- Power = 250 Watts
- Diameter of Probe’s heat shield = 2.7 meters
- (8.9 feet)
- Number of Science Instruments = 6
- Probe Mission Day = 14 January 2005
- Probe Mission Duration = 2.5 hours

## Why such a short mission?

- The environment on Titan’s surface is very cold (temperatures on the surface
- average 95° Kelvin (-178 C, -288° F) and the batteries are not expected
- to last longer than a couple of hours in those conditions.
- Also, the probe will use the Cassini Orbiter as a relay station back to Earth. All
- the science data Huygens collects will be transmitted directly to Cassini. Once
- the Cassini Orbiter dips below Huygens’ horizon, the probe and the orbiter
- will no longer be able to communicate with each other. By the time the orbiter
- returns to Titan, many months will have passed and the probe’s systems will
- be frozen.

## Huygens Descent Profile

- As the probe enters Titan’s atmosphere and slows, a small parachute is
- released which deploys the main probe parachute. Once the parachute is fully
- open the decelerator shield is jettisoned and the probe drifts toward Titan’s
- surface. About 40 kilometers (24.86 miles) above the surface the main chute
- is jettisoned and a smaller drogue chute carries the probe the remaining distance.
- Descent time = 2.5 hours
- Impact Speed = 15 miles per hour
- Surface collection time = 30 minutes

## Cassini’s Launch Vehicle

- The Titan IVB comprises two large, high-thrust solid rocket motors and two
- stages of hypergolic (burn on contact) liquid propellant rockets. The additional
- Centaur upper stage uses cryogenic (super-cold) liquid hydrogen and liquid
- oxygen propellants.
**Height of assembled launch vehicle** = 183 feet
- As a comparison, when the space shuttle with its external
- tank is standing on the launch pad, it is almost as tall as the Titan IVB.
- The Apollo/Saturn V rocket series was twice as tall.
**Lift Capacity** = 5,770 kilograms (12,700 pounds). This is approximately the same
- weight as a school bus.

## Sending Cassini to Saturn

- Liftoff occurred at 4:43 am Eastern Time on 15 October 1997.
- Launch Location = Cape Canaveral Air Force Station in Florida.

**Did you know?**
- The total launch mass (including the
- Titan IVB, Cassini, and the launch
- propellant was 1 million kilograms
- (2.2 million pounds).

## Getting to Saturn

- Cassini is much to heavy to go directly from Earth to Saturn. To minimize the
- fuel required to reach Saturn, Cassini uses the concept of gravity assist.
- Gravity assist is a process where Cassini uses the gravity of another planet to
- give it a push in velocity.
- On its way to Saturn, Cassini flew
- by Venus (2), Earth, and Jupiter.
- This is known as a
- Venus-Venus-Earth-Jupiter
- Gravity Assist (VVEJGA).

## Cassini’s Flyby Dates

- Venus = 26 April 1998 - altitude 337 km (210 miles)
- Venus = 24 June 1999 - altitude 598 km (374 miles)
- Earth = 18 August 1999 - altitude 1166 km (725 miles)
- Jupiter = 30 December 2000 - altitude 9,721,846 km (6,076,154 miles)

## Earth’s Moon

- Cassini flew past the Earth and Moon on 18 August 1999.
- The spacecraft’s closest approach to the Earth was 1166 kilometers
- (725 miles) which occurred at 03:28 UTC.

## Io Close-Up

- Jupiter’s moon Io floats above the planet’s cloud tops in this image
- captured by the Cassini spacecraft’s Imaging Science Subsystem
- on the dawn of the new millennium, January 1, 2001, two days after
- Cassini’s close approach to Jupiter.

**Did you know?**
- There is room for two and one-half
- Jupiters between Io and Jupiter’s cloud
- tops.
- Io is approximately the size of Earth’s
- Moon.

## Io and Jupiter

- This image of Jupiter with Io in the foreground was taken on December
- 12, 2000. This image was taken at a distance of 19.5 million kilometers
- (12.1 million miles) from Jupiter.

## Gas Ring Around Jupiter

- A doughnut-shaped ring of gas surrounding Jupiter is made visible in this
- Image captured in extreme ultraviolet wavelengths by the Cassini spacecraft.
- The ring called the Io torus, draws its raw material from gases spewed by
- Volcanoes on Io.

## Io Torus

- Io is volcanically active because tides are raised within it by the gravity of
- Europa and massive Jupiter. These movements are so enormous that they
- continually heat and melt the interior. The gases released in eruptions are
- ionized by interaction with Jupiter’s radiation belt, creating a trail of
- “ionized exhaust.” This trail is called a “torus.”

## Radio Emissions at Jupiter

- These data were collected over a 6.5 hour time period on December 3, 2000.
- The Cassini Spacecraft was at a distance of just over 27 million kilometers.

## Cassini Science Targets

- Cassini’s 5 groups of science objectives at Saturn are:
- 	Saturn - the planet and its atmosphere
- 	Saturn’s Rings
- 	Titan - landing site for the Huygens Probe
- 	Saturn’s 29 known “Icy Satellites”
- 	Magnetosphere

## Saturn Science Objectives

- Saturn Science Objectives:
- a) Determine the temperature field, cloud properties, and composition Saturn’s atmosphere.
- b) Measure the global wind field, including wave and eddy components; observe synoptic
- cloud features and processes.
- c) Infer the internal structure and rotation of the deep atmosphere.
- d) Study the diurnal variations and magnetic control of the ionosphere of Saturn.
- e) Provide observational constraints (gas composition, isotope ratios, heat flux) on
- scenarios for the formation and the evolution of Saturn.
- f) Investigate the sources and the morphology of Saturn lightning (Saturn Electrostatic
- Discharges and lightning whistlers).

## Rings Science Objectives

- Rings Science Objectives:
- a) Study the configuration of rings and dynamical processes (gravitational, viscous,
- erosional, and electromagnetic) responsible for ring structure.
- b) Map composition and size distribution of ring material.
- c) Investigate interrelation of rings and satellites, including imbedded satellites.
- d) Determine dust and meteoroid distribution in the vicinity of the rings.
- e) Study interactions between the rings and Saturn’s magnetosphere, ionosphere, and
- atmosphere.

## Enhanced Color of Rings

- some of the possible variations in the chemical composition in the ring system.

**How big are those ring particles?**
- Typical ring particle sizes range from micrometers (roughly the size of
- cigarette smoke) to tens of meters and larger.

## Ring Spokes

- Spokes form at a distance from Saturn where the rotational speed of the ring
- particles matches that of the planet’s magnetic field lines. Further studies of
- spokes link their formation to regions on Saturn associated with intense long-
- wavelength radio emissions.
- Spokes appear rapidly as the ring rotates toward the dawn terminator and then
- diffuse gradually near the dusk terminator.
- They are composed of micrometer sized particles.

- Spokes were originally discovered when the Voyager spacecraft flew past
- Saturn in the early 1980s.

## Titan

- Titan has a thick atmosphere that is primarily composed of Nitrogen.
- 	Nitrogen ~ 95%
- 	Methane ~ 5%
- 	traces of hydrocarbons and hydrogen cyanide
- Distance from Saturn = 1,222,000 km (759,478 miles)
- Orbital Period = 15.94 days
- Diameter = 5150 km (3200 miles) - 40% the diameter of Earth
- Surface Temperature = 95° Kelvin (-178° C, -288° F)

**Did you know?**
- Titan has a larger diameter than Mercury or Pluto.

## How big is Titan?

- and the Galilean Satellites.

- Diameter of each body in the image:
- Mercury = 4,880 km (3,033 miles)
- Venus = 12,100 km (7,520 miles)
- Earth = 12,756 km (7,928 miles)
- Mars = 6,788 km (4,219 miles)
**Titan = 5,150 km  (3,200 miles)**
- Ganymede = 5,280 km (3,282 miles)
- Io = 3,640 km (2,262 miles)
- Europa = 3,000 km (1,865 miles)
- Callisto = 5,000 km (3,108 miles)

## Titan Science Objectives

- Titan Science Objectives:
- a) Determine the abundance of atmospheric constituents (including any noble gases),
- establish isotope ratios for abundant elements, constrain scenarios of formation and
- evolution of Titan and its atmosphere.
- b) Observe vertical and horizontal distributions of trace gases, search for more complex
- organic molecules, investigate energy sources for atmospheric chemistry, model the
- photochemistry of the stratosphere, study formation and composition of aerosols.
- c) Measure winds and global temperatures; investigate cloud physics, general circulation,
- and seasonal effects in Titan’s atmosphere; search for lightning discharges.

## Titan’s Surface

- region close to the large continental mass.

- In 1994, the WF-PC2 on the Hubble Space Telescope provided the first glimpse
- below Titan’s cloud layer. A large white area approximately the size of
- Australia was seen in the Hubble image. Because the region rotates at the
- same rate as Titan, it is believed that the large white region is a surface feature.

**Did you know?**
- Titan’s surface could be partially
- covered with lakes of liquid
- hydrocarbons.

## Titan vs. Earth Atmosphere

- While Titan is only 40% the diameter as Earth, Titan’s atmosphere extends 10 times
- higher than Earth’s atmosphere.
- Titan’s atmosphere is composed primarily of nitrogen (90-97%) and methane (2-10%).
- Earth’s atmosphere is composed
- primarily of nitrogen (78%) and
- oxygen (21%).
- Note that a commercial jet flies at
- an altitude of approximately 30,000
- feet (5.7 miles or 9.14 km)

## Icy Satellites

- Saturn has 29 known “icy satellites” that are named after figures in Greek and
- Roman mythology.
- The orbital mechanics of Saturn’s satellites are very complex. Some are embedded
- in rings, some are co-orbital (two satellites sharing the same orbital distance from
- Saturn), some are shepherd satellites, and some are Lagrangian satellites.

**Did you know?**
- All but 2 of Saturn’s satellites rotate
- synchronously (they always show the same
- face toward Saturn just like Earth’s
- Moon does).

## Icy Satellite Objectives

- Icy Satellites Objectives:
- a) Determine the general characteristics and geological histories of the satellites.
- b) Define the mechanisms of crustal and surface modifications, both external
- and internal.
- c) Investigate the compositions and distributions of surface materials, particularly
- dark, organic rich materials and low melting point condensed volatiles.
- d) Constrain models of the satellites’ bulk compositions and internal structures.
- e) Investigate interactions with the magnetosphere and ring systems and possible gas
- injections into the magnetosphere.

## Shepherd Satellites

- Shepherd satellites are believed to play a key role in defining the edges of
- Saturn’s A-ring and F-ring. Atlas lies several hundred kilometers from the
- outer edge of the A-ring. Prometheus and Pandora orbit on opposite sides of
- the F-ring. It is believed that Prometheus and Pandora constrain the width of
- the F-ring and may cause the ring’s kinky appearance.
- The Shepherd Satellites are: Atlas, Prometheus, and Pandora.

## Lagrangian Satellites

- Lagrangian satellites orbit in the Lagrangian points of larger satellites. These
- are locations within an object’s orbit in which a less massive body can move
- in an identical, stable orbit.
- Lagrangian points lie 60° in front of or behind the larger satellite.
- Which are the Lagranian satellites of Saturn?
- Helene is the Lagrangian satellite to Dione
- Calypso and Telesto and Lagrangian satellites of Tethys

## Pan

- Discovered by: Mark Showalter (1990)

- Physical Data:
- Diameter (irregular shape)= 20 km
- Distance from Saturn = 134,000 km (83,750 miles)
- Mass = unknown

- Name Origin: Pan was the Greek god of nature and the forest. He was a creature
- resembling a man with the hind legs and hooves of a goat.

**Did you know?**
- Pan orbits within the A-Ring and helps to clear the Encke Gap in the A-Ring.

## Atlas (AT-less)

- Discovered by: Richard Terrile and the Voyager team (1980).

- Physical Data:
- Diameter (irregular shape)= 37 km x 34.4 km x 26.4 km
- Distance from Saturn = 138,000 km (86,250 miles)
- Mass = unknown

- Name Origin: The son of Iapetus. After the defeat of the Titans, Zeus ordered
- Atlas to uphold the vault of the sky.

**Did you know?**
- Atlas helps to confine particles at the outer edge of the A-Ring.

- Atlas is one of the Lagrangian satellites.

## Prometheus (pro-MEE-thee-us)

- Discovered by: Stewart Collins and the Voyager team (1980).

- Physical Data:
- Diameter (irregular shape)= 148 km x 100 km x 68 km
- Distance from Saturn = 139,000 km (86,875 miles)
- Mass = 3.69 x 1017 kg (5.05 x 10-6 times our moon’s size)

- Name Origin: Son of Iapetus.

- Prometheus is one of the shepherd satellites

## Pandora

- Discovered by: Stewart Collins and the Voyager team (1980).

- Physical Data:
- Diameter (irregular shape)= 110 km x 88 km x 62 km
- Distance from Saturn = 142,000 km (88,750 miles)
- Mass = 3.01 x 1017 kg (4.11 x 10-6 times our moon’s size)

- Name Origin: Pandora means “many gifts.” Pandora was a work of art who was
- transformed into a human by the gods.

- Pandora is one of the shepherd satellites.

## Epimetheus

- Discovered by: telescope observation (1966).

- Physical Data:
- Diameter (irregular shape)= 138 km x 110 km x 110 km
- Distance from Saturn = 151,000 km (94,375 miles)
- Mass = 7.67 x 1017 kg (1.05 x 10-5 times our moon’s size)

- Name Origin: brother of Prometheus, husband of Pandora. Epimetheus was a
- Titan and one of the three original judges of dead souls.

**Did you know?**
- Epimetheus and Janus move in almost identical orbits at about two and a half
- Saturn radii. They are called “co-orbital” satellites.

## Janus

- Discovered by: Telescope observation (1966)

- Physical Data:
- Diameter (irregular shape)= 194 km x 190 km x 154 km
- Distance from Saturn = 151,000 km (94,375 miles)
- Mass = 2.75 x 1018 kg (3.76 x 10-5 times our moon’s size)

- Name Origin: An exalted Roman god and a figure of great antiquity and obscure
- origin. Always represented as having 2 faces (one looking forward and one
- looking backwards), Janus presided over the past, present, and future, over gates,
- doorways, entrances, and beginnings in general, and over war and peace.

**Did you know?**
- Because Epimetheus orbits slightly faster than Janus, Epimetheus overtakes Janus
- in their orbit once every four years.

## Mimas (MY-muss)

- Discovered by: William Herschel (1789)

- Physical Data:
- Diameter (irregular shape)= 418.2 km x 392.4 km x 382.8 km
- Distance from Saturn = 186,000 km (116,250 miles)
- Mass = 5.18 x 1019 kg (7.10 x 10-4 times our moon’s size)

- Name Origin: A Giant killed by the god Hephaestus and transformed into a
- rock hill.

**Did you know?**
- Mimas has an enormous crater on one side that nearly split the satellite apart.

## Enceladus (n-SELL-uh-dus)

- Physical Data:
- Diameter (irregular in shape) = 512.6 km x 494.4 km x 489.2 km (~310 miles)
- Distance from Saturn = 238,000 km (148,750 miles)
- Mass = 1.15 x 1020 kg (1.57 x 10-3 times our moon’s size)

- Discovered by: William Herschel (1789)

- Name Origin: a giant and son of the Titans. Enceladus means “battle cry.”

**Did you know?**
- Enceladus is very bright and may re-supply the E-ring with material through
- water eruptions.

## Tethys (TEE-this)

- Name Origin: wife of the powerful Titan Oceanus who ruled the seas before
- Poseidon. Tethys was the mother of all sea nymphs and of all rivers on Earth.

- Discovered by: Jean Dominique Cassini (1684)

- Physical Data:
- Diameter (irregular shape)= 1071 km x 1056 km x 1051 km
- Distance from Saturn = 295,000 km (184,375 miles)
- Mass = 1.03 x 1021 kg (1.41 x 10-2 times our moon’s size)

- P-23948

**Did you know?**
- Tethys has two “lagrangian” moons: Telesto and Calypso.

## Telesto (tel-LESS-toe)

- Discovered by: Brad Smith, Steve Larson, and Harold Reitsema (1980).

- Physical Data:
- Diameter (irregular shape)= 30 km x 25 km x 15 km
- Distance from Saturn = 295,000 km (184,375 miles)
- Mass = unknown

- Name Origin: A muse whose specialty has been forgotten (muses were minor
- goddesses that represented human activities such as music or medicine).

## Calypso (kuh-LIP-soh)

- Discovered by: Don Pascu (1980)

- Physical Data:
- Diameter (irregular shape)= 30 km x 16 km x 16 km
- Distance from Saturn = 295,000 km (184,375 miles)
- Mass = unknown

- Name Origin: A nymph whose name means “I hide.” Calypso lived alone on
- an island until she fell in love with the mortal sailor and explorer Odysseus.

## Dione (die-OH-nee)

- Name Origin: An ocean nymph, mother of the goddess Aphrodite.

- Physical Data:
- Diameter = 1120 km (696 miles)
- Distance from Saturn = 377,000 km (234,625 miles)
- Mass = 1.43 x 1021 kg (1.96 x 10-2 times our moon’s size)

- Discovered by: Jean Dominique Cassini (1684)

**Did you know?**
- Dione shares and orbit with Helene.

## Helene (huh-LEE-nee)

- Discovered by: Pierre Laques and Jean Lecacheux (1980).

- Physical Data:
- Diameter (irregular shape)= 35 km
- Distance from Saturn = 378,000 km (236,250 miles)
- Mass = unknown

- Name Origin: An Indo-European Earth goddess who, with her twin sister
- Clytemnestra, had been hatched from an egg. Helene’s twin brothers are the
- Gemini twins Castor and Pollux.

## Rhea (REE-uh)

- Physical Data:
- Diameter = 1528 km (950 miles)
- Distance from Saturn = 527,000 km (329,375 miles)
- Mass = 3.39 x 1021 kg (4.65 x 10-2 times our moon’s size)

- Discovered by: Jean Dominique Cassini (1672)

- Name Origin: Wiife of Kronos and mother of the Olympian gods Zeus, Poseidon,
- Hades, and the goddesses Demeter, Hera, and Hestia.

**Did you know?**
- At 1528 km in diameter, Rhea is the second largest satellite of Saturn.

## Hyperion (high-PEER-ee-on)

- Name Origin: A Titan, father of of the pre-Olympian god Helios (the Sun),
- the goddess Selene (the Moon), and the goddess Eos.

- Discovered by: William Bond, George Bond, and William Lassell (1848).

- Physical Data:
- Diameter (irregular shape) = 350 km x 280 km x 225 km
- Distance from Saturn = 1,481,000 km (925,625 miles)
- Mass = 2.42 x 1019 kg (3.31 x 10-4 times our moon’s size)

- P-23936

**Did you know?**
- Hyperion has an odd shape (like a hamburger patty) and rotates chaotically
- due to the gravitational influence of Titan.

## Iapetus (eye-AP-eh-tuss)

- Physical Data:
- Diameter = 1436 km (892 miles)
- Distance from Saturn = 3,561,000 km (2,225,625 miles)
- Mass = 2.56 x 1021 kg (3.51 x 10-2 times our moon’s size)

- Discovered by: Jean Dominique Cassini (1671)

- Name Origin: One of the Titans and father of Atlas, Epimetheus, Prometheus,
- and Menoetius.

**Did you know?**
- Iapetus’ leading face is only 1/6 as bright as its trailing face.

## Phoebe (FEE-bee)

- Discovered by: William Pickering (1898).

- Physical Data:
- Diameter (irregular shape)= 230 km x 220 km x 210 km
- Distance from Saturn = 12,561,000 km (7,850,625 miles)
- Mass = 5.46 x 1018 kg (7.48 x 10-5 times our moon’s size)

- Name Origin: Phoebe was the youthful goddess of Earth’s Moon, forests,
- wild animals, and hunting.

**Did you know?**
- Phoebe is possibly a captured asteroid, with a 550-day retrograde orbit and a
- 9-hour rotation period.

## Saturn’s “New” Satellites

- New telescopic capabilities and more sophisticated observing techniques have
- led to a flurry of new moon discoveries throughout the solar system. Saturn
- is no exception. In the past few years, 12 new moons have been discovered
- orbiting the ringed planet. This brings the current total to 30.
- To keep current on the different attributes of these new discoveries, watch the
- Cassini Mission web site, astronomy sites, or print publications on the subject.

**Did you know?**
- Saturn is the current leader in the “moon race” at 30. Its neighbor Jupiter ranks
- second with 28 moons.

## Saturn’s Magnetosphere

- Magnetic fields such as those of Earth and Saturn are approximated by a dipole
- (a simple structure with a north and south pole like a bar magnet).

- There is no measurable off-set between the magnetic dipole and Saturn’s
- rotation axes. This is unique in the Solar System (by comparison, Earth’s
- Magnetic field is off-set from the rotation axis by 11.4°).

**What is a magnetosphere?**
- Saturn generates a magnetic field that shields the planet, its rings, and moons
- from the solar wind. This shield is called a “magnetosphere.”

## Magnetospheres Objectives

- Magnetospheres Objectives:
- a) Determine the configuration of the nearly axially symmetric magnetic field and
- its relation to the modulation of Saturn Kilometric Radiation (SKR)
- b) Determine current systems, composition, sources, and sinks of magnetospheric
- charged particles
- c) Investigate wave-particle interactions and dynamics of the day-side magnetosphere
- and the magnetotail of Saturn and their interactions with the solar wind, the
- satellites, and the rings.

## Arrival at Saturn

- Saturn’s gravity, Cassini’s main engine must burn for 90 minutes. This maneuver,
- called Saturn Orbit Insertion or SOI, is also the time when the spacecraft comes
- closest to the rings.

- Saturn Orbit Insertion will occur on 1 July 2004.
- Cassini will pass through the gap between Saturn’s F-Ring and G-Ring.
- Closest Distance during SOI = 60,330 km

## Initial Orbit

- Following the SOI burn, Cassini will make a large orbit through the Saturn system.
- This first orbit will last 148 days.
- This long initial orbit will set up the geometry for the first encounter with Titan and
- the Huygens Probe mission.
- The Probe will be released on 25 December 2004 and will arrive at Titan on
- 14 January 2005.

## Touring the Saturn System

- During the four years, the spacecraft will make approximately 74 orbits
- of Saturn, using Titan turn Cassini’s orbit.
- Orbits will range in length from 7 to 155 days.
- Cassini’s orbital distance from Saturn will
- range from 156,858 km
- to 953,214 km and the spacecraft’s orbit
- will change from equatorial to
- inclined at approximately 70°.
- Cassini will make 43 flybys of Titan
- during the tour.