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