Transcript Two Kinds of Planets - Physics and Astronomy

Info for the Test
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Bring a #2 pencil.
No electronic devices: No cell phones, headphones,
etc.
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No books, notes, etc.
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No hats.
Grades will be posted on the Mastering Astronomy
website.
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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)
Origin of Pluto
Now known to be just one of the largest 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?
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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.
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.
Greenhouse Effect
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What is the greenhouse effect and how does it
differ on Earth and on Venus?
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.
Tides
What causes the tides?
When are the highest (and lowest) tides seen?
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.
Mercury
Mass = 0.055 MEarth
Radius = 0.38 REarth
Surface Temp: 100 - 700 K
Average distance from Sun =.39 AU
Moonlike: Surface craters, no
atmosphere (escaped long ago due to
high surface temp & low mass)
Orbital period = 88 days
Rotation period = 59 days (Exactly 2/3
of Mercury’s year!)
Composite image from Mariner 10 1970s
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?
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"Radar Mapping" technique measures altitude
space probe
time for signal to return tells you the
altitude of surface feature.
Planet Surface
Anomalous rotation of Venus
• Extremely slow - Venutian solar 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
Properties of the Planets
Which planet has the largest known volcano
in the solar system?
Olympus Mons
Largest known volcano in Solar System – 3X the height of Everest!
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"
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.
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
- 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.
- Temperature difference between zones and belts => different chemistry =>
different coloration.
- Gas in zones and belts flow in opposite directions.
Differential Rotation
What is differential rotation and what types of
objects rotate in this way?
- Different latitudes rotate at different rates - fluid
Objects!
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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.
Origin of Saturn's Rings:
If a large moon gets too close to a planet, the tidal force breaks it apart
into small pieces. The radius where this happens is called the Roche
Limit (approximatly 2.5 x planet radius). Satellite must be held togther
solely by its own gravity + must have similar density to planet for this
to be an appropriate limit.
Total mass of ring particles equivalent to moon 250 km in diameter.
All ring systems in Solar System within or close to Roche Limit.
Voyager probes found that rings divide into 10,000's of ringlets.
What maintains this ringlet structure?
Gaps in Rings:
Narrow gaps: Swept clean by small moonlets embedded
within the rings. Moonlets are much larger than largest
ring particles -> simply attract ring material as they
orbit, leaving a less dense area.
Cassini Division due to gravitational force of Saturn's
innermost medium sized moon – particles are deflected
into new orbits.
Formation of Rings:
Rings are young -> must either be newly
formed or periodically replenished.
Possible explanations: replacement by moon
fragments chipped off by meteoric impacts
and/or moon torn apart by tidal forces.
Recall this will be the fate of Neptunes moon
Triton.
Saturn's Large Moon – Titan – A moon with a thick
atmosphere (lower temp than Jupiter's moons)
Saturn's moon – has an appreciable atmosphere
Mission which landed on its surface in 2005 – Cassini
-One of the main reasons Scientists find Titan so interesting is it may present an opportunity to
study the kind of chemistry which occurred billions of years ago on Earth.
-Cassini mission landed on Titans surface for the first time in 2005.
Granular Materials
Saturn's Rings
Landers
Dynamics of Meteor Impacts
“River Channels” on Mars?