Transcript Document

Two Kinds of Planets
"Terrestrial"
"Jovian"
Two Kinds of Planets
"Terrestrial"
"Jovian"
Mercury, Venus,
Earth, Mars
Jupiter, Saturn,
Uranus, Neptune
Distance from Sun?
Size?
Composition?
Density?
Rotation Rate?
Number of moons?
Rings?
Heavy or light elements?
Two Kinds of Planets
"Terrestrial"
"Jovian"
Mercury, Venus,
Earth, Mars
Jupiter, Saturn, Uranus, Neptune
Close to the Sun
Small
Mostly Rocky
High Density
Slow Rotation (1 - 243 days)
Few Moons
No Rings
Heavy Elements (Fe, Si, C, O)
Far from the Sun
Large
Mostly Gaseous
Low Density
Fast Rotation (0.41 - 0.72 days)
Many Moons
Rings
Light Elements (H, He)
What about Pluto?
Origin of Pluto
Now known to be just a relatively large member of a class of
objects in the outer reaches of the Solar System:
The Kuiper Belt Objects
Questions
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What are some of the smaller objects (or debris)
found in the solar system?
What is the main reason that we study these
smaller objects? (What information do they
contain that the planets and moons do not?)
Questions
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What are some of the smaller objects (or debris)
found in the solar system?
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Comets, asteroids, meteoroids
What is the main reason that we study these
smaller objects? (What information do they
contain that the planets and moons do not?)
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Solar system debris is unevolved => gives direct
evidence of conditions during solar system formation!
Comet Structure
Nucleus: ~10 km ball of ice, dust
Coma: cloud of gas and dust around nucleus (~106 km
across)
Tail: can have both ion and dust tails (~108 km long).
Always points away from Sun.
Solar System Formation
Our solar system started out as a giant cloud of cold
gas that collapsed under its own gravity.
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So, why is our solar system flat?
Conservation of angular momentum!
What role did dust play in the formation of our solar system?
Condensation theory:
1) Dust grains act as "condensation nuclei": gas atoms stick
to them => growth of first clumps of matter. Also radiate heat
=> help to cool gas => faster gravitational collapse.
What term describes the process by which smaller particles
collide and stick together to form larger clumps?
Condensation theory:
1) Dust grains act as "condensation nuclei": gas atoms stick
to them => growth of first clumps of matter. Also radiate heat
=> help to cool gas => faster gravitational collapse.
2) Accretion: Clumps collide and stick => larger clumps.
Eventually, small-moon sized objects: "planetesimals".
3) Gravity-enhanced accretion: objects now have significant
gravity. Mutual attraction accelerates accretion. Bigger
objects grow faster => a few planet-sized objects.
Atmosphere and Greenhouse Effect
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What is the greenhouse effect and how does it
differ on Earth and on Venus?
What type of EM radiation do the greenhouse
gasses in our atmosphere trap?
What type of EM radiation does the ozone layer
of our atmosphere protect us from?
Runaway Greenhouse Effect on Venus
The Interior of the Earth
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How does temperature vary as we get closer to
the core of the Earth?
What about density?
Earth's Internal Structure
Temperature and density
increase with increasing
depth.
How do we obtain
information about the
structure of the Earth's
interior?
Like all waves, seismic waves bend when they encounter changes
in density. If density change is gradual, wave path is curved.
S-waves are unable to travel in liquid.
Measurement of seismic waves gives info about density of Earth's
interior and which layers are solid/molten.
The Tides
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What causes the tides?
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When are the highest (and lowest) tides seen?
Tides
Questions
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What are the two main features of the lunar
surface? Which is older? How do we know?
What is currently the most widely excepted
theory explaining how the moon formed?
The Lunar Surface
Large, dark featureless
areas: "maria" or "seas".
More recent lava flows.
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Lighter areas at higher
elevation: "highlands".
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Many craters (due to
meteorite impacts). Only
important source of
erosion!
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Highlands have 10x the
crater density of maria =>
Highlands are older!
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maria
highlands
Impact Theory
Early in Solar System, when many large planetesimals around, a
Mars-sized object hit the forming Earth, ejecting material from the
mantle which went into orbit around Earth and coalesced to form
Moon. Computer simulations suggest this is plausible.
Properties of the planets
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Which planet exhibits retrograde rotation?
How do we determine the direction and rate
of a planet's rotation?
Anomalous rotation of Venus
• Extremely slow - Venutian day longer than
Venutian year!
• Retrograde - Sun rises in the west and sets in the
east!
• Most likely due to a collision during solar
system formation
Determining rotation rate of a planet
• Use reflected radio waves to determine line of
sight doppler shifts.
Venus
• Thick clouds prevent viewing
of surface. (UV Image)
• High temperatures and
pressures, acidic gases, make
it difficult to land anything on
surface.
• Led to much speculation.
• How did we get info about
surface?
"Radar Mapping" technique measures altitude
space probe
time for signal to return tells you the
altitude of surface feature.
Planet Surface
Properties of the Planets
Which planet has the largest known volcano
in the solar system?
Olympus Mons
Mars
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What is the main reason that many scientists think
Mars may have once harbored life?
What is the most likely origin of the two moons
of Mars?
Evidence for Past Surface Water
"runoff channels" or
dry rivers
"outflow channels"
standing water erosion in craters?
teardrop "islands" in
outflow channels
Mars' Moons Phobos and Deimos
Deimos: 16 x 10 km
Phobos: 28 x 20 km
Properties similar to asteroids. They are probably
asteroids captured into orbit by Mars' gravity.
Question
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Jupiter and Saturn were known to the ancient
astronomers. Uranus, which is barely visible to
the naked eye, was discovered in 1781.
Neptune is not visible to the naked eye, so how
was it discovered?
Discovery of Neptune
Neptune predicted to exist because of
irregularities in Uranus' orbit.
Neptune discovered in 1845 by Johann Galle.
Gravitational perturbation of Uranus’ orbit by
unseen planet led to discovery of Neptune!
Kepler’s and Newton’s laws in action!
Nice example of how the scientific method
works!
Jupiter's Bands
Lighter-colored "zones" and darker-colored "belts".
Belt
Zone
Shadow of a moon
Great Red
Spot
Question
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Zones and belts are, respectively, high and low
pressure systems on Jupiter.
What process would you expect to be taking place
between such regions?
Why do the zones and belts stretch all the way
around Jupiter?
- Zones and belts are Jupiter's high and low pressure systems, respectively.
- They mark a convection cycle.
- Jupiter's rapid rotation stretches them horizontally around the entire planet.
- Gas in zones and belts flow in opposite directions.
Differential Rotation
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What is differential rotation and what types of
objects rotate in this way?
Differential Rotation
Rotation period of Jovians is shorter closer to the
equator:
Near poles
At equator
Jupiter
9h 56m
9h 50m
Saturn
10h 40m
10h 14m
Uranus
16h 30m
14h 12m
How do we know? Tracking storms at various
latitudes, or using Spectroscopy and Doppler shift.
The Galilean Moons of Jupiter
(sizes to scale)
Closest to Jupiter
Furthest from Jupiter
Would you expect Jupiter to be hotter or cooler very early in its history? What
might this imply for the Jupiter-Galilean moon system?
The Galilean Moons of Jupiter
(sizes to scale)
Closest to Jupiter
Furthest from Jupiter
The Galilean Moons resemble a miniature planetary system in many
ways! Intense heat of young Jupiter played role of sun.
Io's Volcanism
More than 80 volcanoes have been observed. Can last months or years.
Largest is bigger than Maryland - emits more energy than all Earth volcanoes
combined!
Io is about the size of our moon. Why is it's volcanic activity surprising?
Where is the energy coming from?
Io and Europa are in a resonance orbit:
Start clock now
Jupiter
Europa
Io
One orbit of Io
Jupiter
Europa
Io
Two orbits of Io
Jupiter
Europa
Io
The periodic pull on Io by
Europa makes Io's orbit
elliptical and distorts
entire moon.
Jovian Rings
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How did Saturn's rings form?
Origin of Saturn's Rings:
If a large moon, held together by gravity, gets too close to Saturn, the
tidal force breaks it apart into small pieces. The radius where this
happens is called the Roche Limit.
Total mass of ring particles equivalent to moon 250 km in diameter.
Voyager probes found that rings divide into 10,000's of ringlets.
What maintains this ringlet structure?
Shepherd Moons
• Some ringlets
maintained by
gravitational influence
of “shepherd moons”
• Keep particles from
straying outside the
path of the ringlet