Neptune

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Size comparison of the Outer Planets
Earth
Neptune
Uranus
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Early telescopic observations of Saturn
a. Galileo, 1610 b. Huygens 1655 c. Cassini
1676
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Spacecraft that have visited Saturn

• Pioneer 11 flew within 21,000 km of Saturn on 1
  September 1979, discovered two new moons and an
  additional ring, charted Saturn's magnetosphere
  and magnetic field and found its planet-size moon
  Titan, to be too cold for life.
• The Voyager 1 and 2 Saturn encounters occurred
  nine months apart, in November 1980 and August
  1981. Discovers larger of internal to external
  heat 2-to-1 compared to 1-to-1 for Jupiter.
• Cassini orbital insertion on July 1, 2004. Took
  first image of a moon (Phoebe) on June 11, 2004.
  Still working in April 2006
• http//photojournal.jpl.nasa.gov/mission/Cassini
  
• Cassini dropped the Huygens probe into atmosphere
  of Titan on January 14, 2005.

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Cassini spacecraft launched on Oct. 15, 1997
from KSC
7 Year cruise on Venus-Venus-Earth-Jupiter Gravity
Assist Trajectory
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The Cassini Spacecraft
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Interior Structure of Saturn
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Like on Jupiter, there are latitudinal bands of
clouds and storms
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Ribbon clouds in atmosphere high-speed
turbulence
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Wind speeds at top of Saturns Atmosphere
Opposite direction
1700 km/hr
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Multiple Rings!
Encke Gap
Cassini Division
C
D
B
F
A
E Ring extends to 7.5 Saturn radii from cloud top
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Structure Non-symmetric on each side of Saturn
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Braided F-Ring of Saturn due to co-orbiting
shepherd moons
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Two shepherd satellites confine Saturns narrow F
ring. The outer shepherd gravitationally
deflects ring particles inward, and the inner
shepherd deflects ring particles outward.
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Prometheus
ltRgt 47 km, Density 0.42
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Pandora
ltRgt 41 km, Density 0.54
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Ring Spokes Dust above the ring plane
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The Smaller Moons of Saturn
Janus
Telesto
Prometheus
Helene
Atlas
Calypso
Pandora
Epimetheus
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Janus
ltRgt 90 km, Density 0.61
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Epimetheus ltRgt 58 km, Density 0.64
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Mimas, 392 km in diameter Herschel Crater is 130
km wide and 10 km deep!
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Enceladus 500 km in diameter Diverse surface,
with some tectonics
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Enceladus
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Tethys 1,060 km in diameter. Heavily cratered,
with some lineaments
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Dione 1,120 km in diameter. Bright surface
swirls, many craters
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Rhea 1,530 km in diameter. Very heavily cratered
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Various spacecraft views of Titan 5,150 km in
diameter
Cassini visible light image
Pioneer 11
Cassini near-IR image
Voyager 1
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What do we know about Titan?

• It is the biggest of Saturns moons.
• Titans diameter of 5,150 km makes it larger than
  the planet Mercury with a diameter of 4,880 km
  and Pluto (2,350 km).
• Only Jupiter's moon Ganymede is larger.
• Three-and-a-quarter Earth Moons could fit inside
  Titan.
• Titan is the only moon known to have a large
  atmosphere maybe thicker than Earths (gt1,000
  mb)!
• Its atmosphere is mostly nitrogen, just like the
  atmosphere surrounding Earth, but thicker.
• Its atmosphere contains methane and tiny amounts
  of oxygen.

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Comparison of Titans atmosphere with Earths
Important gases in Titans atmosphere
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• Ethane-methane lakes 2. Moist convection
  in methane clouds
• 3. Sedimentation of aerosols 4. Elevated
  terrain washed by rain

3.
2.
1.
4.
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January 14, 2005 Huygens Probe sent to Titans
surface
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Huygens scientific instruments

• Aerosol Collector and Pyrolyzer collects Titan's
  aerosols for chemical composition analysis
• Descent Imager/Spectral Radiometer makes
  spectral measurements and takes pictures of
  Titan's surface and atmospheric hazes
• Doppler Wind Experiment uses radio signals to
  deduce wind speeds on Titan
• Gas Chromatograph/Mass Spectrometer identifies
  and quantifies various atmospheric constituents
  on Titan
• Surface Science Package determines the physical
  properties of Titan's surface.

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Radar Image of Titans surface valley systems
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Few impact craters seen on Titan implies young
surface
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Surface image from Huygens probe
Horizon at 66 m
30 cm diameter
Range 240 cm
15 cm diameter
Range 85 cm
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Iapetus 1,460 km in diameter. Striking albedo
differences
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Cassini Views of Iapetus
Iapetus is 1,460 km diameter Orbits 59.1 Saturn
radii from planet
100 km
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Whats Interesting about Phoebe?

• Phoebe is roughly spherical and is 220 km in
  diameter.
• Phoebe rotates on its axis every 9 hours and
  orbits Saturn in 18 months.
• Its irregular, elliptical orbit is inclined 30
  degrees toward Saturns equator.
• Phoebes orbit is retrograde.
• Phoebes average distance from Saturn is 13
  million km, which is 4 times farther away from
  Saturn than its nearest neighbor, the moon
  Iapetus.
• Phoebe and Iapetus are the only major moons in
  the Saturn region that do not orbit close to the
  plane of Saturns equator.
• Unlike most major moons orbiting Saturn, Phoebe
  is very dark and reflects only 6 percent of the
  sunlight it receives.

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Saturns moon Phoebe
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Identification of surface materials on Phoebe
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Saturn Summary