Info for the Test

Bring a #2 pencil.

No electronic devices: No cell phones, headphones, etc.

No books, notes, etc.

No hats.

Grades will be posted on the Mastering Astronomy website.

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)

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 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.

Greenhouse Effect

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

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.

TidesWhat 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.

● 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.

MercuryMass = 0.055 M

Earth

Radius = 0.38 REarth

Surface Temp: 100 - 700 KAverage 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 planetUse reflected radio waves to determine line of

sight doppler shifts.

VenusThick 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

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 MonsLargest 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"

teardrop "islands" in outflow channels standing water erosion in craters?

Mars' Moons Phobos and Deimos

Phobos: 28 x 20 kmDeimos: 16 x 10 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".

Shadow of a moonGreat Red Spot

Belt

Zone

- 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!

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.

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 moon – has an appreciable atmosphere

Mission which landed on its surface in 2005 – Cassini

Saturn's Large Moon – Titan – A moon with a thick atmosphere (lower temp than Jupiter's moons)

-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

Landers

Dynamics of Meteor Impacts

Saturn's Rings

“River Channels” on Mars?