Outline

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Lecture 21
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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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• Why is the ecliptic at an angle with respect to
  the horizon?

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Inferior planets
superior planets
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A planets synodic period is measured with
respect to the Earth and the Sun (for example,
from one opposition to the next)
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Periods

• Rotational
• Orbital
• Sidereal
• Synodic

Measured with respect to something that is not
rotating or orbiting
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Orbit

• http//learning.nd.edu/orbital/orbitals.swf

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Question

• Which is longer, Jupiters synodic or orbital
  period?
• Which is longer, Jupiters synodic or Saturns
  synodic period?
• Guess Jupiters and Saturns synodic period.

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Question

• As seen from Earth, does Jupiter or Saturn
  undergo retrograde motion more frequently?

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Keplers Third Law

• P2 a3
• P planets sidereal period, in years
• a planets semimajor axis, in AU

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Long orbital periods of Jupiter and Saturn cause
favorable viewing times to shift
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The best time to observe Saturn from Earth is
when it is

1. at opposition and it is midnight at your location
   on Earth.
2. at opposition and it is sunset or sunrise at your
   location on Earth.
3. at conjunction and it is midnight at your
   location on Earth.
4. at conjunction and it is sunset or sunrise at
   your location on Earth.
5. at opposition and it is just before sunrise at
   your location on Earth.

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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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What happens to ornaments when hoop is spun?
hoop
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hoop
A
B
C
D
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The oblateness of Jupiter and Saturn reveals
their rocky cores

• Jupiter probably has a rocky core several times
  more massive than the Earth
• The core is surrounded by a layer of liquid
  ices (water, ammonia, methane, and associated
  compounds)

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The oblateness of Jupiter and Saturn reveals
their rocky cores

• On top of this is a layer of helium and liquid
  metallic hydrogen and an outermost layer composed
  primarily of ordinary hydrogen and helium
• Saturns internal structure is similar to that of
  Jupiter, but its core makes up a larger fraction
  of its volume and its liquid metallic hydrogen
  mantle is shallower than that of Jupiter

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Metallic hydrogen inside Jupiter and Saturn
endows the planets with strong magnetic fields

• Jupiter and Saturn have strong magnetic fields
  created by currents in the metallic hydrogen
  layer
• Jupiters huge magnetosphere contains a vast
  current sheet of electrically charged particles
• Saturns magnetic field and magnetosphere are
  much less extensive than Jupiters

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Synchrotron Radiation

• Charged particles in the densest portions of
  Jupiters magnetosphere emit synchrotron
  radiation at radio wavelengths

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Auroras on Jupiter and Saturn are caused by

1. charged particles from the magnetosphere
   colliding with molecules in the upper atmosphere.
2. ionized hydrogen.
3. ionized helium.
4. tidal interactions with the largest moons.
5. gas circulating at the poles.

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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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Atmospheres

• gravity and escape velocity

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Atmospheres

• gravity and escape velocity

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Atmospheres

• The visible surfaces of Jupiter and Saturn are
  actually the tops of their clouds

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Atmospheres

• The rapid rotation of the planets twists the
  clouds into dark belts and light zones that run
  parallel to the equator

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The chemical composition of Jupiter and Saturn is
difficult to measure. Why?
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Atmospheres

• The outer layers of both planets atmospheres
  show differential rotation
• The equatorial regions rotate slightly faster
  than the polar regions

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Atmospheres

• For both Jupiter and Saturn, the polar rotation
  rate is nearly the same as the internal rotation
  rate

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Spacecraft images show remarkable activityin the
clouds of Jupiter and Saturn
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The internal heat of Jupiter and Saturn has a
major effect on the planets atmospheres
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• Explain how Infrared and Visible (indicated on
  the previous slide) relate to the blackbody
  curves we studied.

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A space probe has explored Jupiters deep
atmosphere

• There are presumed to be three cloud layers in
  the atmospheres of Jupiter and Saturn
• The reasons for the distinctive colors of these
  different layers are not yet known
• The cloud layers in Saturns atmosphere are
  spread out over a greater range of altitude than
  those of Jupiter, giving Saturn a more washed-out
  appearance

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Both Jupiter and Saturn emit more energy than
they receive from the Sun. What does this tell
us?
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Jupiter radiates more energy into space than it
receives from the Sun. What is the primary source
of the excess energy that Jupiter radiates?

1. Decay of radioactive materials in Jupiter's core
2. Tidal forces from Jupiter's moons
3. Jupiter is still contracting, and the contraction
   releases energy
4. Jupiter's rotation is slowing down dramatically,
   and this slowdown releases energy
5. All of the above are the energy sources

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What can you say about these planets?
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If Jupiter and Saturn formed at the same time,
which should be emitting more heat?
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• Saturns atmosphere contains less helium than
  Jupiters atmosphere
• This lower abundance may be the result of helium
  raining downward into the planet
• Helium rainfall may also account for Saturns
  surprisingly strong heat output

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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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• Link

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Something is Fishy

• How can a planet be solid?

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Earth-based observations reveal three broad rings
encircling Saturn
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• Saturn is circled by a system of thin, broad
  rings lying in the plane of the planets equator
• This system is tilted away from the plane of
  Saturns orbit, which causes the rings to be seen
  at various angles by an Earth-based observer over
  the course of a Saturnian year

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Saturns rings are composed of numerous icy
fragments, while Jupiters rings are made of
smallrocky particles

• The principal rings of Saturn are composed of
  numerous particles of ice and ice-coated rock
  ranging in size from a few micrometers to about
  10 m
• Jupiters faint rings are composed of a
  relatively small amount of small, dark, rocky
  particles that reflect very little light

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• Most of its rings exist inside the Roche limit of
  Saturn, where disruptive tidal forces are
  stronger than the gravitational forces attracting
  the ring particles to each other
• Each of Saturns major rings is composed of a
  great many narrow ringlets

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Saturns rings consist of thousands of
narrow,closely spaced ringlets
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Saturns inner satellites affect the
appearanceand structure of its rings
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Outline

• Jupiter and Saturn
• Orbit
• Surface
• Atmosphere
• Rings
• Moons

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Preview

• Already discussed influence on Saturns rings.
• Jupiters moons are even more interesting

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