The Solar System

• Observations– Ordered motions of objects– Two types of planets – Terrestrial (Solid) vs. Jovian

(Gas)• For example, Mars vs. Jupiter

– Asteroids and comets– Meteoroids, Meteors, Meteorites– Exceptions to ordered motions

• Tilt of Earth’s axis, Earth’s Moon, Pluto

• Is there a theory that can explain what we see? Yes!!

The Solar System:Sun, Terrestrial, and Jovian planets

Terrestrial (inner) planets•Small•contains the heavier elements (Fe, Si, O)•rocky shell over a metallic core•Accretion began 4.567 billion years ago•It took about 0.1 billion years(100 million years) for planets to form

Juvian (outer) planets•mostly volatile gases (H,He)•same composition as the sun,but internal pressure is too lowfor nucleo-synthesis to take place

99.8 % of the total mass of the solar system resides in the sun

Solar Nebular Theory

• Solar System formed through the collapse of a large cloud of gas under its own gravity

Lagoon Nebula

Eagle Nebula

Nebular TheoryNebular Theory

NebulaNebula

Cloud of dust and gas in space

Formation of our solar system:The nebular hypothesis (Kant, 1755)

Gravitational Collapse

• Lets look at an animation!

Angular Momentum Conservation also explains why objectsrotate faster as they shrink in radius:

From Cloud to Solar System• Energy Conservation

– As the nebula contracts, the energy is concentrated in a smaller area. This, in turn, heats the cloud

• Ang. Momentum Cons.– Causes the cloud to spin

faster

• Cloud Flattens– The lighter material floats

to the outer edges. – The more dense material

stays towards the center.– In our solar system, this

was the formation of our inner solid and outer gaseous planets.

How do planets form?• Through accretion (collecting of material)

– Small particles are able to build larger complexes of particles through electromagnetic forces

– Eventually the complex becomes large enough to “attract” pieces through gravitation – planetesimals

– Only the largest planetesimals survive to become planets

– The smaller pieces collide and merge with the larger ones or are broken up by gravitational forces

• Question: Why are all of the planets very nearly spherical in structure?

Formation of our solar system:The nebular hypothesis (Kant, 1755)

PlanetesimalsPlanetesimals

Formation of our solar system:The nebular hypothesis (Kant, 1755)

Why are there two types of planets?

• It boils down to temperature!• Gas in the solar nebula was

mostly hydrogen and helium, but there were trace amounts of hydrogen compounds, rock, and metals

• Inner parts of disk are “hotter” than outer parts

• Rocks can be solid at much higher temperatures than ice

• Inside the “frost line” too hot for hydrogen compounds to form

• Outside the “frost line” cold enough for gases and ices to condense

Examples Condensation Temperature

Relative Abundance in Solar System

Hydrogen and Helium Gas

Hydrogen (H), Helium (He)

Do not condense in nebula

98%Hydrogen Compounds

Water (H20), Methane (CH4), Ammonia (NH3)

< 150 K 1.4%

Rock Various 500 – 1300 K .4%

Metals Iron (Fe), Nickel (Ni), Aluminum (Al)

1,000 – 1,600 K .2%

Planet Formation

• Terrestrial planets (Mercury, Venus, Earth, and Mars) all formed 0.3 AU from the sun.Rock could condense beyond this distance

• Jovian planets (Jupiter, Saturn, Uranus, and Neptune) all formed beyond the frost line (3.5 AU)– Hydrogen compounds formed the cores of these planets

• Continues to support nebular theory• What about planet orbits?

– But more questions remain

Earth formation

Nebula forms out of H, He cloudsand fusion products from now dead stars.

Gravity pulls gas and dust inward, and rotationmakes a accretionary disk. The proto-sun is atthe center and fusion begins when it is hot enough.

Heavier elements concentrate in the inner rings. Collisions andgravitational attraction leads to the formation of planetesimals.

Gravity reshapes theproto-Earth into a sphere

Soon after Earth formed, a Mars-size planet collided withEarth, blasting debris into space that will form our Moon.

Volcanic gases form the atmosphere, and as Earthcools, moisture condenses and rains into oceans.Some gases may have come from passing comets.

Does this theory make sense?

• We observe many other stars forming from interstellar clouds with circumstellar disks

• What has yet to be explained?

1.1. List the 9 planets in our solar system. List the 9 planets in our solar system.

MercuryMercuryVenusVenusEarthEarthMarsMarsJupiterJupiterSaturnSaturnUranusUranusNeptuneNeptunePluto (dwarf planet)Pluto (dwarf planet)

2. List each planet and the 2. List each planet and the main facts about each. main facts about each.

MercuryMercury• smallest planet

• no atmosphere

• heavily cratered

• smooth terrain (north)

(old volcanic activity)

• deep slopes

• 1 rotation = 59 days

• 1 revolution = 88 days

• Temp: 800 F to -279 F

VenusVenus

• 1 revolution: 225 days

• 1 rotation: 243 days

•Thick clouds

• Volcanic and Tectonic activity (present)

• 80% plains covered by volcanic flows

• Temp: 887 F

• Atmosphere is 97% CO2

EarthEarth

• The Oasis of the Solar SystemThe Oasis of the Solar System• 1 rotation: 23 hours, 56 minutes1 rotation: 23 hours, 56 minutes• 1 revolution: 365.24 days1 revolution: 365.24 days• Liquid waterLiquid water• Plenty of nitrogen and oxygenPlenty of nitrogen and oxygenneeded for lifeneeded for life

• Earth rotates at 1,532 ft per secEarth rotates at 1,532 ft per sec•Earth revolves at 18 miles per secEarth revolves at 18 miles per sec

MarsMars• The red planet (FeO)

• 1 rotation: 24 hours, 37 min.

•1 revolution: 687 days

• White polar caps

• Large dust storms

• Hurricane force winds

• Large volcanoes and canyons (Olympus Mons and Valles Marineris)

• Temp: - 94 F to – 148 F

•Two moons: Phobos and Deimos (asteroids)

The Asteroid Belt

• Asteroids are small bodies that are left over from the beginning of the solar system

• They are rocky objects with round or irregular shapes up to several hundred km across, but most are much smaller.

• May be the remains of an early planet which broke up.

• The chances of an asteroid colliding with Earth are very small! But some do come close to Earth, like Hermes (closest approach of 777,000 km).

JupiterJupiter

• largest planet (11 earths in face)

• 1 rotation = 10 hours

• 1 revolution = 12 years

• Great RED Spot – a cyclonic storm

• hydrogen-helium atmosphere

• winds cause light and dark bands

• immense gravity

• gigantic ocean of liquid hydrogen

• 63 moons (Europa, Io, Callisto, Ganymede)

SaturnSaturn

• 1 revolution: 29.46 years

• 1 rotation: 10 hours, 39 minutes

• Rings (10 m thick) made of ice and rock particles

• Winds up to 637.5 mph

• Large cyclonic storms

• 60 moons (Titan, Mimas (death star))

UranusUranus

• Rotates on its side (98o)

• Complex ring system

• 1 revolution: 84.01 years

• 1 rotation: 17 hours, 54 min

• 27 moons (Miranda, Puck)

The Kuiper Belt

• Region of the Solar System extending beyond the planets extending from the orbit of Neptune to the outer edge of the solar system

• Similar to the asteroid belt, but objects are frozen or icy.• comets: lumps of ice and dust, tails point away from the

sun, have very long orbital periods.

• Examples of Comets: Halley’s (76 years), Hale-Bopp (Heaven’s Gate Cult), Shoemaker-Levy (plunged into Jupiter in 1994).

• Interactive Comet Animation

Kuiper Belt

NeptuneNeptune

• Discovered in 1846, mathematical prediction

• 1 revolution: 164 days

• 1 rotation: 18 hours

•Winds up to 625 mph

• Great DARK spot – a large rotating storm

• 13 moons (Triton)

PlutoPluto

• Smaller than our moon!

• 1 revolution: 248 years

• 1 rotation: 6 days, 9 hours

• classified as a dwarf planet

• Average temp: 346 F

• Dirty ice ball• Part of Kuiper Belt?• Old Moon of Neptune?

List the terrestrial planets.List the terrestrial planets.

MercuryMercuryVenusVenusEarth Earth MarsMars

What does the term, “terrestrial” mean?What does the term, “terrestrial” mean?

Earth-like

List the jovian planets. List the jovian planets.

Jupiter

Saturn

Uranus

Neptune

What does the term, “jovian” mean?What does the term, “jovian” mean?

Jupiter-like

What are the terrestrial planets made of?What are the terrestrial planets made of?

Rocky and metallic substances

What are the jovian planets made of?What are the jovian planets made of?

Hydrogen and Helium Gas

H compunds

(ex. Ammonia, Methane)

PlanetesimalsPlanetesimals

Small, irregular shaped bodies resulting from colliding bits of matter.

Asteroids and Comets

Ida Hale-Bopp

• Asteroids – Rocky leftover planetesimals• Comets - Icy leftover planetesimals

AsteroidAsteroidSmall rocky bodies

CometCometPieces of rocky and metallic materials

ComaComaThe glowing head on a comet

MeteoroidMeteoroidA small solid particle traveling through space.

When is a meteoroid When is a meteoroid called a shooting star?called a shooting star?

When it enters the earth’s atmosphere.

MeteorMeteor

A meteoroid that burns up in earth’s atmosphere.

MeteoriteMeteoriteA meteoroid that reaches the earth’s surface.

Other Solar Systems?

• Nearly 600 others detected

• Can not detect directly– Even for the largest

planets, light from the star overwhelms any light from the planet

• Use indirect evidence to search for planets– Gravitational tugs