Announcements

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Announcements

• Website
• Homeworks posted
• Lectures up to date
• Star party tonight
• Meet at 7pm
• Need transportation
• Venus transit

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Roche limit (Math addendum 5, last section)
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Roche limit continued
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Roche limit
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Roche limit example
R.Ring 274000km/2 137,000 km
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Saturns rings are composed of numerous icy
fragments.

• Doppler shift measurements confirm that inner
  rings are spinning faster, and are separated
  from, outer rings.
• The rings move following Keplers third law
  suggesting that they are composed of individual
  moonlets or ring particles.
• Ring particles range in size from 1 cm to 5 m
  with 10 cm being most common.
• The ring particles reflect 80 of the light that
  falls on them (albedo) which is consistent with
  water ice.
• Tidal forces pull larger ring particles apart
  within a critical distance from Saturn, called
  the Roche Limit.

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Saturns rings consist of thousands of narrow,
closely spaced ringlets.
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Saturns inner satellites affect the appearance
and structure of its rings.
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Saturns inner satellites, called SHEPHERD
SATELLITES, affect the appearance and structure
of its rings.
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Saturn is less brightly banded than Jupiter
Same 3 layers, but atmosphere is thicker, so we
dont see different colored layers as well. This
is due to Saturns lower surface gravity
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Saturns internal structure is similar to that of
Jupiter, but contains less liquid metallic
hydrogen.
This, along with less gravity and less mass, also
allows it to be less oblate.
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Saturns Satellites

• One planet sized satellite, Titan
• Intermediate in size between Mercury and Mars.
• Six moderate-sized satellites
• Very low densities (probably mostly ice).
• All synchronously orbit in the Saturns
  equatorial plane.
• Twenty-eight tiny satellites
• Might be captured asteroids.
• Might be jagged remnants of collisions.

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Titan has a thick, opaque atmosphere rich in
methane, nitrogen and hydrocarbons.
The surface of Titan, the second largest moon in
the solar system, is obscured by thick clouds.
Originally in the form of NH3, the Suns
radiation likely liberated the hydrogen which
escaped. Methane probably condenses into
droplets and falls as rain.
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The dark patches have lower IR reflectivity which
could be liquid hydrocarbon seas or large
expanses of solid organic material. The bright
yellow could be highly reflective continents.
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
The smallest of the six has an enormous impact
crater among many other craters.
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
Few craters and many ice flows on its young
surface suggests internal tidal heating from
Dione and Saturn
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
Mostly heavily cratered with a curious, smooth
plains region of solidified water and ammonia
lava.
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
Dione has a heavily cratered leading side and a
smooth trailing side.
e
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
Also has a heavily cratered leading side and a
smoother trailing side.
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
Also has a heavily cratered leading side which is
abnormally dark and a smoother and brighter
trailing side.
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The icy surfaces of Saturns six moderate-sized
moons provide clues to their histories.
The six seem to come in pairs of sizes.
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A Saturn-orbiting spacecraft, CASSINI, and a
Titan lander, HUYGENS, will provide a wealth of
new information.

• Arriving in about 2004, the enormous Cassini
  spacecraft will spend four years orbiting Saturn
  and studying the planet, rings, and moons.
• The Huygens Probe will detach and parachute into
  Titans atmosphere sending back detailed
  information before it crashes into the surface.
• The orbits have been significantly reconfigured
  to account for any Doppler shifts in Huygens
  radio transmissions.

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Cassini Spacecraft
RPWS (University of Iowa)
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University of Iowa RPWS Instrument

• The objective of the RPWS investigation is to
  study radio and plasma waves in the vicinity of
  Saturn and during the flight to Saturn. This
  objective includes studies of
• Radio emissions
• Plasma waves
• Lightning
• Dust impacts
• Plasma densities and temperatures
• Plasma density fluctuations
• Regions investigated include
• Saturn's magnetosphere
• Titan's ionosphere
• Solar wind
• Jupiter's magnetosphere
• Earth, Venus, and Asteroids

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Where is Cassini right now?
Jupiter orbit
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Cassini Orbit at Saturn
Saturn
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Huygens Probe Descent into Titans
atmosphere(November 27, 2004)
Impact will be 15 mph. If Huygens probe survives,
it will transmit data for about 30 min.
Probe weighs 350 kg (770 lbs), diameter 2.7m (8ft)
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Cassini Orbits after Huygens probe(4 year
mission planned)
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Saturn Review Questions

• Who discovered that Saturn has rings?
• Galileo (1610), although he didnt see rings
  clearly. Huygens (1655) was the first astronomer
  to clearly see and report the rings
• Are Saturns rings actually solid bands that
  encircle the planet?
• No, they are small particles independently
  orbiting Saturn
• What is the composition and size of the ring
  particles?
• Ring particles are ice and ice-covered rocks,
  size from microns to 10m
• How do Saturns satellites affect the shape of
  its rings?
• There are several gaps in the rings which are
  tidally resonant with satellites, e.g. Cassini
  division and satellite Mimas (12 period, 11.3 h
  vs 22.6 h)
• Why are the color variations in Saturns
  atmosphere less dramatic than those on Jupiter?
• Saturn is less massive (1/3 Jupiter), so surface
  gravity is less, and three layers of the
  atmosphere (NH3, NH4SH, H2O) are more extended
  (300km vs. 75km) so we mostly see the top layer
  only.
• Why is Saturn more oblate than Jupiter?
• Saturn has similar rotation period but less
  gravity, so its more oblate (10 vs. 6)
• How does Saturns atmospheric helium compare with
  Jupiter?
• Saturns atmosphere has much less helium (3 vs.
  13 by number),
• Why does Saturn, emit even more radiation than it
  receives from the Sun than Jupiter?
• Helium rain droplets may have fallen deep into
  interior, releasing heat from gravitational energy

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Saturn Review questions cont

• How is it possible for Saturns moon Titan to
  have an atmosphere? (It is the only solar system
  satellite with an atmosphere)
• Titan is both massive enough and cool enough to
  retain heavy hydrocarbons in its atmosphere.
• What is Titans atmospheric composition?
• Mostly hydrocarbons e.g. methane, ethane,
  acetylene.
• What kinds of geologic activity are seen on
  Saturns other satellites?
• Enceladus has a geologically young surface
  (very icy, high albedo, few craters), probably
  caused by tidal heating from Saturn and the
  satellite Dione
• What plans are there for future exploration of
  the Saturnian system?
• Cassini (launched 1997) will arrive at Saturn in
  July 2004, launch Huygens probe into Titans
  atmosphere (Nov 2004)