ASTR-1010 Planetary Astronomy

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ASTR-1010Planetary Astronomy

• Day - 33

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Yuri Gagarin 12 April 1961
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Course Announcements
This Weeks Lab Comparative Planetology Homework
Chapter 9 Due Wednesday April 14. Homework
Chapter 10 Due Monday April 19. Homework Chapter
11 Due Friday April 23. Homework Chapter 12 Due
Wednesday April 28. Homework Chapter 21 Due
Wednesday April 28. -this is extra credit. The
last 1st Quarter moon observing nights
are Tuesday (April 20) Thursday (April
22) 800 pm both nights.
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Uranus, Neptune Pluto
The Discovered Worlds
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William Herschel discovered Uranus in 1781
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John Adams Urbain Le Verrier Predicted Neptune
in 1846
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Johann Galle actually discovered Neptune on
September 23, 1846
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The Facts on Uranus
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The Facts on Neptune
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Size Comparison of Earth, Uranus Neptune
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Uranus rotates on its side
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There are a few storms in the atmosphere of Uranus
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Neptune has a more active atmosphere than Uranus
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Hubble Observations of Neptune
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Uranus Neptune have similar internal structures
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Chapter 11Lecture Outline

• Moons, Rings, and Dwarf Planets

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Gallery of Moons
NASA/JPL/Caltech
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Jovian Planets

• Jovian planets
• Jupiter, Saturn, Uranus, Neptune
• Sunlight is too weak to provide much energy
• J, S, N all have internal energy production
• All have massive magnetic fields
• Surface gravities Appendix
• Densities light materials

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Jovian Moons

• All have moons Appendix (150 and growing)?
• Big moons these are the interesting ones (for
  us)?
• Small moons just so much space junk
• 1610 Galileo discovered 4 bodies orbiting
  Jupiter (the Galilean moons)
• 1656 Huygens discovered Titan at Saturn
• By 1700 Cassini 4 more at Saturn

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Jupiter

• Galileo's observing notes - 1610

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Galilean Moons Today
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Moons and Rings

• Dozens of worlds of rock and ice exist in our
  Solar System.
• They have many diverse properties, only partially
  understood.
• Give us opportunities to test our ideas of
  physics and planet formation.

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Regular and Irregular Moons

• Most of the larger moons formed with their
  planets.
• These are called regular moons.
• Some are captured bodies, usually on retrograde
  (backwards) orbits.
• These are called irregular moons.

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Major Moons

• The four gas giants have several large moons.
• Many of these are as large as Earths Moon.
• Some are geologically active.
• Others show activity in the distant past.

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Big Moons

• G, Titan are larger than Mercury
• E, C, I, and Triton are larger than Pluto
• Our Moon is 5,
• Between E I in size
• Orbit planet in proper direction. (mini-SS).

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Small Moons

• Irregular shapes
• High inclination orbits
• Some retrograde
• Highly elliptical orbits
• Suggest captured asteroids or KBOs or TNOs
• Triton

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Large Moons Formation

• The largest moons formed the same way the
  terrestrial planets did.
• Major processes accretion and differentiation.
• Biggest difference with the terrestrials
  composition.
• Large moons have more ices (frozen water,
  methane, etc.) and less rock (silicates).

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Formation

• Formed in the proto-planetary nebula, along with
  host planet.
• Gives
• Orbit direction
• composition

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Composition

• Ices could condense
• Rock and ice found
• Low average densities
• Variation within systems
• Temp. gradient in P-PN
• Jupiter water ice
• Probably nothing else
• Outer planets
• Water, methane, other

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Accretion and Differentiation
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Rotation

• Nearly all show synchronous rotation
• Keep same side toward host planet
• Results from tidal forces
• Tidal drag
• Europa very slight deviation

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Earth

• Tidal friction lengthens the day by 1 second in
  about 50,000 years.

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Earth

• Tidal friction lengthens the day by 1 second in
  about 50,000 years (Earth spin slows).
• Conservation of angular momentum requires that
  the moon move farther away.

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Io

• Tidal heating 1979 Voyager 1 volcanoes
• Close to Jupiter strong tidal forces
• Slightly elliptical orbit large changes in
  tidal force

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Orbital Resonance

• 421 (IEG)?
• Moving out toward Callisto (not currently in
  resonance orbit).

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Other Heat Sources

• Radioactive decay
• Internal generation
• Iapetus
• May have had liquid or soft interior at one time.