# Presentation: 171053

## Cassini-Huygens

- Mission to the Saturn System

## The Destination

- Saturn is best known for its magnificent ring system. But the Saturn system is
- a unique environment combining rings, moons, and the planet.
**Saturn Facts**
- Saturn is the second largest planet in the Solar System.
- Titan, the largest moon, has a thick nitrogen-rich atmosphere.
- Saturn emits 79% more energy than it receives from the Sun.
- Saturn receives 1/90th the amount of
- sunlight Earth receives.

## Saturn and Earth Compared

- If you placed Saturn and its main rings (excluding the diffuse E-ring) between
- The Earth and the Moon, Saturn would barely fit.
- Earth-Moon distance = 384,000 km (239,000 miles)
- Saturn and ring system diameter =340,000 km (211,310 miles)

## Tour Highlights

- Some of the exciting events early in the Saturn tour include:
- Phoebe encounter - 11 June 2004 (closest approach is 2,000 km, 1243 miles)
- Saturn Orbit Insertion - 1 July 2004
- Huygens Probe Release -
-         25 December 2004
- Huygens Probe Mission -
-          14 January 2005

- Cassini will spend 4 years orbiting the Saturn system. During that time, the
- spacecraft will make 75 orbits about the planet and 45 flybys of Titan.

## Saturn Orbit Insertion

- Date: 1 July 2004
- Approach is from below the ring plane.
- Ascending Ring Plane Crossing at 158,500 km (98,508 miles) from Saturn
- 	1 hour, 52 minutes before periapsis (closest approach)
- Cassini crosses the ring plane between the F- and G-rings.
- Burn Ignition: 01:12 UTC
-     (6:12pm Pacific Time on 30 June)
- Burn Duration = 97 minutes
- Burn Termination: 03:03 UTC
-     (8:03pm Pacific Time on 30 June)
- Velocity Change = 632 m/sec
-     (approximately 1414 mph)

## Touring Saturn

- During the 4-year tour, Cassini will make 75 orbits of Saturn, using Titan to
- turn the spacecraft’s orbit.
- Orbits will range in length from 7 to 118 days.
- Cassini’s orbital distance from Saturn will
- range from 156,858 km
- to 953,214 km (98,036- 592,422 miles).
- The spacecraft’s orbit
- will change orientation from equatorial to an
- inclination of approximately 75°. This
- allows scientists to study Saturn’s polar
- regions.

## Science Targets

- Cassini’s 5 groups of science objectives at Saturn are:

- Saturn’s extensive Rings

- Saturn - the planet and
- its atmosphere

- Titan

- Magnetosphere

- Icy Satellites

## 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).

## Saturn Physical Facts

- 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 receives approximately 1/90th the amount of sunlight the Earth receives.

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

## 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’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.

## 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 Physical Facts

- 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.

## Titan and Earth

- While Titan is only 40% the diameter as Earth, its atmosphere extends 10 times
- higher into space 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%).
- Of course the surface temperature
- on Titan is a chilling 95°K
- (-178°C or -288°F)
- compared to Earth’s balmy
- 290°K (17°C or 63°F)

## Huygens Probe Release

- The Huygens Probe has no onboard thrusters. Therefore, both the orbiter and
- the probe will be placed on a collision course with Titan.
- The probe release is scheduled for 24 December 2004
- 3 days following the probe release,
- the orbiter will perform an orbit deflection
- maneuver, moving the spacecraft off its
- collision course with Titan and placing
- it on the correct trajectory to relay the
- probe data to Earth.
- The probe will continue its 21 day journey
- to Titan, arriving at the moon on
- 14 January 2005.

## The Probe’s Descent to Titan

**Descent**
- 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 or 7 m/sec
- (comparable to a skydiver landing
- with an open parachute)
- Surface collection time = 30 minutes

## Landing Location

- While mathematics allow
-  us to pin down the latitude
- of Huygens’ landing
- location, we cannot identify
- the landing longitude so
- accurately. This is because
- we do not have a
- good understanding of the
- prevailing winds on Titan.
-                   Landing Location: -10° latitude (±0.7°), 160° E longitude (±13°)

## 	Why such a short mission?

- The environment on Titan’s surface is very cold (temperatures on the surface
- average 95° Kelvin which is -178 C, -288° F) and the batteries are not expected
- to last longer than a couple of hours in those conditions.

- 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.

## 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.

## Saturn’s Magnificent Rings

- Saturn’s rings are made primarily of water ice. False color images of Saturn’s
- rings show different colors that illustrate some of the possible variations in
- chemical composition.

**Did you know?**
- Typical ring particle sizes range
- From micrometers (roughly the
- size of cigarette smoke) to ice
- boulders larger than tens of meters.

## Cassini’s Ring Focus

- The mission will focus on four critical questions:
- How did the rings form?
- How old are the rings?
- How are the rings maintained?
- What are the dynamics and
- relationships of the rings to Saturn,
- its satellites, and its electromagnetic
- fields?

## 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.

## Icy Satellite Facts

- The term “icy satellites” serves to separate Titan from the other, smaller moons.
- Before 2000, Saturn had 17“icy satellites”. Today there are 29 recognized
- “icy satellites” of Saturn.
-    - The original 17 are named after figures in Greek and Roman mythology.
-    - The 12 new additions carry temporary names.

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

## Icy Satellite Highlights

- Mimas has an enormous crater on one side hat nearly split the satellite apart.

- Iapetus - with one hemisphere extremely reflective and the other as dark as black velvet, this satellite has a split personality.

- Enceladus is very bright and may re-supply the E-ring with
- materials through water eruptions.

## More Unique Satellites

- Hyperion has an odd shape (like a hamburger patty) and rotates
- chaotically due to the gravitational influence of Titan.
- Tiny Pan orbits within Saturn’s A-ring and helps clear the
- Encke Gap of material.

- Phoebe does her own thing taking 550 days to orbit the planet.
- And that orbit is retrograde meaning she travels backward to
- her neighbors.

## Lagrangian Satellites

- Lagrangian satellites are pairs of moons that share an orbit. A small satellite
- orbits in the Langrangian point of a larger satellite.
- Lagrangian points are locations within an object’s orbit where a less massive
- body can move in an identical, stable orbit.
- Lagrangian points lie 60° ahead or behind the larger satellite.

**Which are the Lagrangian Satellites of Saturn?**
- Helene is the Lagrangian satellite of Dione
- Calypso and Telesto are Lagrangian satellites of Tethys.

- Tethys

## Shepherd Satellites

- Shepherd Satellites help constrain the ring material, helping define the edges
- of the rings they orbit with.
- Atlas lies several hundred
- kilometers from the outer edge
- of the A-ring.
- Prometheus and Pandora orbit on
- opposite sides of Saturn’s F-ring.

**Did you know?**
- 16 of Saturn’s moons, including Titan and Iapetus, rotate synchronously
-  (they always show the same face toward Saturn just like Earth’s moon does).

## Co-orbital Satellites

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

- Janus and Epimetheus move in almost identical orbits at about two and one-half
- Saturn radii. This is 151,000 kilometers (94,375 miles).
- They are called “co-orbital” satellites because of this.

- Janus

- Epimetheus

## 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.

## Magnetosphere Facts

- 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.”