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Two Kinds of Planets
"Terrestrial"
"Jovian"
Two Kinds of Planets
"Terrestrial"
Mercury, Venus,
Earth, Mars
"Jovian"
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"
Mercury, Venus,Earth, Mars
"Jovian"
Jupiter, Saturn, Uranus, Neptune
Close to the SunSmallMostly RockyHigh Density Slow Rotation (1 - 243 days)Few MoonsNo RingsHeavy Elements (Fe, Si, C, O)
Far from the SunLargeMostly GaseousLow Density Fast Rotation (0.41 - 0.72 days)Many MoonsRingsLight 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
● 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
● What are some of the smaller objects (or debris) found in the solar system?
– 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?)
– Solar system debris is unevolved => gives direct
evidence of conditions during solar system formation!
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.
Comet Structure
Solar System Formation
Our solar system started out as a giant cloud of cold
gas that collapsed under its own gravity.
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
● 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
● 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
● What causes the tides?
● When are the highest (and lowest) tides seen?
Tides
Questions
● 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.
● Lighter areas at higher
elevation: "highlands".
● Many craters (due to
meteorite impacts). Only
important source of
erosion!
● Highlands have 10x the
crater density of maria =>
Highlands are older!
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
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
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"
teardrop "islands" in
outflow channels standing water erosion in craters?
Mars' Moons Phobos and Deimos
Phobos: 28 x 20 km
Deimos: 16 x 10 km
Properties similar to asteroids. They are probably
asteroids captured into orbit by Mars' gravity.
Question
● 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".
Shadow of a moonGreat Red Spot
Belt
Zone
Question
● 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
● 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:
Jupiter
Saturn
Uranus
Near poles At equator
9h 56m
10h 40m
16h 30m
9h 50m
10h 14m
14h 12m
How do we know? Tracking storms at various
latitudes, or using Spectroscopy and Doppler shift.
The Galilean Moons of Jupiter
Closest to Jupiter Furthest from Jupiter
(sizes to scale)
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
Closest to Jupiter Furthest from Jupiter
(sizes to scale)
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
Europa
Io
Jupiter
One orbit of Io
Europa
Io
Jupiter
Two orbits of Io
Europa Io
Jupiter
The periodic pull on Io by
Europa makes Io's orbit
elliptical and distorts
entire moon.
Jovian Rings
● 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