The Outer Planets. The Moon.

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Lecture 34

• The Outer Planets. The Moon.

Chapter 16.9 ? 16.16

• The Origin of the Moon
• The Outer Planet Family

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Summary of Terrestrial Planets
All the planets are relatively small (diameter lt
13,000 km) Composition rocks and metals (mean
densities 3-5 g/cm3) Density of water is 1
g/cm3 The planets are closely spaced (mean
distance between them is 0.4 A.U.) 1 Astronomical
Unit (A.U.) is the mean distance between the Sun
and the Earth 150 million kilometers The
outermost planet, Mars, is located 1.5 A.U. from
the Sun
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The Moon
The Moon is the largest satellite of a planet in
the inner solar system. The mean distance from
the Earth is 384,000 km. Diameter 3476 km (27 of
the Earths diameter) Mass is 1/81 of the Earths
mass Average density is 3.3 g/cm3 (60 of the
Earths)

• Hypotheses of the Moons origin
• Forming together with Earth and splitting
• Captured by the Earth fully formed
• Double-planet
• Collision

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What Do We Need to Learn?
Why is there a large gap between the two families
of planets? What did cause the differences in
the structures, compositions, and surroundings of
the two families?
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Jovian Planets Basics

• Distance 5-30 AU
• Much farther from Sun than terrestrial planets
• Much colder (100-50 K)

• Mass 10-100 Earth masses
• Much more massive than terrestrial planets

• Jupiter Saturn are similar
• Size (about 10 Earth diameters)
• Composition mostly hydrogen and helium

• Uranus Neptune are similar
• Smaller than Jupiter Saturn
• Less hydrogen and helium

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Basic Parameters
Planet Dist. A.U. Mass MEarth Radius REarth Density g/cm3 Composition
Jupiter 5.20 317 11.2 1.33 H, He
Saturn 9.53 90 9.4 0.70 H, He
Uranus 19.2 14 4.11 1.32 H compounds rock, H, He
Neptune 30.1 17 3.92 1.64 H compounds rock, H, He
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Appearance

• Jovian planets show banded appearance
• due to atmosphere
• we see only cloud tops

• Rotation quite fast (hours)
• Jupiter 10 hrs
• Saturn 11 hrs
• Uranus 17 hrs
• Neptune 16 hrs

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Clouds

• Clouds on Jupiter Saturn
  composed of ammonia ice (NH3)
• different colors due to differing cloud
  composition Saturns clouds deeper less visible

• Clouds on Uranus Neptune
• composed of methane (CH4)
• produces blue-green color

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Planet Interiors
Jupiter
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Planet Density
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Jovian Planet Atmospheres
No solid surfaces Jupiter atmosphere Content
Almost entirely H and He trace amounts of
methane (CH4), ammonia (NH3), and H20. Jupiters
weather occurs in troposphere where clouds can be
formed of ammonia crystals and other compounds
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The Great Red Spot
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Jovian Planet Moons
There are more than 100 known moons orbiting
Jovian planets (J-52, S-30, U-21, N-11)
Three main groups of jovian moons Small moons -
less than 300 km in diameter Medium-size -
300-1500 km Large - more than 1500 km
Medium and large moons have circular orbits that
lie close to the equatorial planes of their
parent planets
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Jupiter Moons
Pre-visit expectations cold and geologically
dead Voyager missions the moons are active!
Four Galilean moons Io, Europa, Ganymede,
Callisto
Io has many volcanoes and no impact
craters Europa no craters, fractured surface,
icebergs Ganymede grooves on surface, magnetic
field Callisto a heavily cratered iceball
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Io
Eruptions erased all Ios impact craters.
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Reasons for Geological Activity
Io has an additional heating source tidal
heating Tidal heating is due to the Ios orbit
ellipticity. Io is continuously flexed by Jupiter.
Source of the orbit ellipticity orbital
resonances Periodical lining up of the three
closest satellites of Jupiter (Io 4 orbits,
Europa 2 orbits, Ganymede 1 orbit)
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Tidal Heating
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Rings and Gaps
Two of Saturns rings can be seen from Earth In
fact, there are as high as 100,000 individual
rings and gaps Rings and gaps are caused by
grouping of particles at some orbital distances
which are being forced out at others.
Gaps can be created by gap moons located within
rings. They clear up gaps around their orbits.
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Rings of SaturnTelescopic view
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Rings of Saturn (Voyager image)
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Rings of Saturn (close up)
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Summary of Jovian Planets

• Jovian planets larger, more massive than
  terrestrial
• Composition
• mostly hydrogen (H) and helium (He)
• dominated by hydrogen
• also large amounts of ices (water, ammonia,
  methane)
• Why So Large?
• basic reason is distance from sun
• cooler temps allowed ices (volatiles) to freeze

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Role of Volatiles

• Inner solar system is hot
• volatiles are gaseous not available for planet
  core formation
• planet cores
• only rock (no ice)
• smaller, less massive (1 earth mass)
• Outer solar system is cold
• volatiles are solid available for planet core
  formation
• planet cores
• both rock and ice
• bigger, more massive (10 earth masses)
• Massive cores have larger gravity can capture
  gas
• Jovian planets have massive atmospheres (lots of
  H and He)
• Terrestrial planets have minimal atmosphere
  (little H and He)

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Summary
The Earths Moon seems to be a result of a
collision with a large proto-planet (Mars
size) Jovian planets are dynamic worlds with
rapid winds, huge storms, strong magnetic fields,
and interiors where common materials strangely
behave. Jovian moons are geologically active
because of their ice compositions. Ring systems
were formed from small moons.