ASTR-1010 Planetary Astronomy

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ASTR-1010Planetary Astronomy

• Day - 34

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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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Observations Requirement

• Attend a 1st Quarter Observing night Counts 3
  of your course grade
• Do a Virtual Observations Counts 3 of your
  course grade
• Write an Observations Report Counts 4 of your
  course grade
• Observations total is 10 of your course
  grade

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Virtual Observations
See the instructions and list of objects on the
handout from the beginning of the
semester orGo to APSU Astronomy, click on
Observing Nights, click on on campus class, go
here then scroll down the page to Virtual
Observation
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How to do theVirtual Observations 1
Install the Starry Night Pro DVD that came with
your textbook on your computer orStay after
lab one day and use the laptops in lab to do the
assignment You can use Starry Night Pro to find
almost all the objects, the named stars and the
planets. A few objects will require a web search.
Try using the NGC/IC Public Database or do a
Google search
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How to do theVirtual Observations 2

• For planets farther from the sun than Earth use
  Starry Night Pro
• Look due south and medium altitude
• Set the date and time to 9pm January 1
• Set the time step to 1 day
• Turn on the planet labels
• Step forward 1 day at a time and look for when
  the planet is due south

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How to do theVirtual Observations 3

• For planets closer to the sun than Earth use
  Starry Night Pro
• Look due east on the horizon
• Set the date and time to 6pm January 1
• Set the time step to 1 day
• Turn on the planet labels
• Step forward 1 day at a time and look for Mercury
  or Venus. Find when they are highest in the sky
• Repeat steps 1-5 looking due west

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Observations Report

• Put all the Virtual Observations information into
  a table that can fit on one or two pages
• Write up information about telescopes, mounts and
  observing aids that were discussed at the 1st
  Quarter Night. A PowerPoint (also pdf) of the
  material can be found on the Observing Nights
  link of www.apsu.edu/astronomy Additional
  information can be found in theSo you wanna buy
  a telescope link.
• Write up a short description of any celestial
  objects you viewed at the 1st Quarter observing
  night or the Lunar Eclipse night.

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Ring Systems

• All four gas giants have ring systems.
• Rings are made of swarms of tiny moons.
• Saturns rings are the largest and brightest.
• The ring particles orbit according to Keplers
  laws.
• Particle orbits are circular collisions or ring
  gravity keep them that way.

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Rings of the Giant Planets
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Saturns Rings

• A very complicated system, composed of thousands
  of ringlets.
• There are bright and dark rings, and gaps.
• Gaps are not empty.
• Brightness/darkness reflects the amount of
  material in each ring.
• The ring system is extremely thin.

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Rings and Ringlets
NASA/JPL/Caltech
NASA/JPL/Caltech
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Saturns Big Ring
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More on Rings

• The rings do not contain much material.
• The mass of all the ring particles is about the
  same as a small, icy moon.
• Rings can be distorted by the gravity of nearby
  moons.

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Rings and Moons
NASA/JPL/Caltech
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Origin of the Rings

• Ring material is from disrupted moons.
• Large moons cannot orbit close to the planet.
• Tidal forces from the planet break up close
  moons.
• Volcanoes or impacts may also supply the rings.
• Saturns rings formed from an icy moon.
• Uranus and Neptunes rings are very dark from
  a body rich in carbon.

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Concept Quiz Ring Velocities

• If you could measure the velocities of ring
  particles at each distance from Saturn, you would
  find
• Inner particles orbit at slower speeds.
• Inner particles orbit at faster speeds.
• Orbital speed is the same at all distances.

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Moons and Rings

• Rings dont last forever.
• Collisions and sunlight would destroy the rings.
• Small, nearby shepherd moons can help stabilize
  the rings.
• The moons also create gaps.
• Cause is orbital resonance orbital period is in
  a ratio with the moon period.

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Large Moons New Worlds

• Spacecraft have explored the larger moons.
• Craters, bright/dark areas reveal geological
  activity.
• Some surfaces old, fully cratered.
• Some surfaces younger Io, Enceladus, Triton
  have active volcanoes or geysers.
• Moons with recent geology must have a source of
  internal heat.

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Internal Heat

• Tidal forces stretch some moons.
• As moon orbits, forces change direction.
• This stretching heats the moons interior.
• Analogy flexing a paper clip.
• Io silicate magma.
• Enceladus ice geysers (cryovolcanism).
• Triton geysers propelled by nitrogen.

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Io
NASA/JPL/Caltech
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Concept Quiz Internal Heat

• You discover a moon of Jupiter. It orbits very
  far from the planet, but it has many volcanoes.
  Is this a surprise?Why?
• No. Any moon can have internal heat.
• Yes. Jupiter is very far from Earths Moon.
• Yes. Tidal forces are less for distant moons.

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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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Titan Possibly Active

• Titan is Saturns largest moon.
• It has a deep, nitrogen-rich atmosphere.
• Currently being explored by the Cassini
  spacecraft.
• Huygens lander revealed icy rocks and a soil
  rich with organic compounds.
• Methane in atmosphere renewed by active geology.

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Titan
NASA/JPL/Space Science Institute
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Old Surfaces

• Most of the larger moons are heavily cratered.
• As with our Moon, this means no recent geology.
• Some craters are extremely large.
• Some moons show fault zones and extensive
  fracturing were they caused by large impacts?

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Mimas
NASA/JPL/Caltech
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Life on Galilean Moons

• Io extreme tidal heating, no water gt no life
• Callisto no tidal heating (not in resonant
  orbit)?
• Ganymede, Europa tidal heating, but might be a
  good thing for these.

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Europa

• Liquid water ocean?
• 1979 Voyager
• Differentiation water
• Smooth surface
• Ice covered
• Galileo s/c long term monitoring
• Subtle variations
• Internal structure

Galileo spacecraft view
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Europa - ocean

• Lack of impact craters, brittle icy crust?
• 80-170 km crust
• Liquid underneath gravitometer measurements
• 1996 magnetic field opposes Jupiter's

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Chaotic terrain
Recent water breakout?
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Evidence for Ocean

• Small number of craters young surface
• Surface features suggest water from below
• Magnetic field something conducts electricity
• Tidal heating supplies enough heat to melt ice.
• Proof will have to wait Europa mission
• Long-wave radar
• Laser altimeter

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Life on Europa

• 3 key elements for life
• Source of elements/molecules to build living
  organisms
• Source of energy for metabolism growth
• Liquid medium for transporting molecules
• Good, indirect evidence of liquid water ocean.
• Expect elements for life in ocean and on floor.
• Possible energy sources, but small wrt Earth.

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Energy question

• But, how do you use it?
• To use warm water energy, you have to have a cold
  sink.
• How wide spread could life be?
• On Earth, very little life derives its energy
  material directly from volcanic vents.

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Ganymede

• Largest in solar system
• Has old and young surfaces
• Intrinsic magnetic field
• Variation of field with Jupiter rotation liquid
• High-density ice forms

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Types of Ice
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Callisto

• Farthest out of the four.
• Old surface.
• Evidence of ice sublimation (powder)?
• Magnetic field ocean?
• Much less energy

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Saturn Beyond

• Titan
• 2nd largest moon in SS
• Thick atmosphere
• 1.5 X Earth pressure
• Cold -180C
• 90 Nitrogen, 0 Oxygen
• Methane, Argon, Ethane
• Lower impact velocities

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Cassini - Huygens
Coastline-like features No pooling of liquids
Huygens landing site dry Cassini evidence of
lakes rivers
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Cassini - Huygens
Wind blown dunes?
Cassini evidence of lakes rivers Liquid
methane lakes near pole?
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Life on Titan?

• Solid ice, no liquid water
• Other liquid hydrocarbons (methane)?
• Slower chemical reaction rates
• UV produces a lot of organic molecules in the
  atmosphere. These should settle out and build on
  the surface.
• Energy sources?
• Cryovolcanoes?
• Acetylene reactions

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Enceladus

• Several of Saturn's moons show evidence of past
  geological activity.
• Enceladus - current activity.
• Fresh ice
• Ice spray water?
• Subsurface ocean
• ammonia/water mix
• Tidal heating

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Triton

• Backwards orbit
• Suggests captured KBO
• Resurfacing actions
• Internal heat source
• Tidal heating
• Radioactive decay?
• Cryovolcano activity

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Uranus has thin rings and several moons
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The Moons of Uranus