Announcements

• 25 people have still not joined the class on Astronomy Place. You can not get credit until you “join the class”. Once you join, all your previous submissions will show up in my gradebook.

• Planet Assignment 4, due Monday March 1, – Part 1: Astronomy Place tutorial “Shaping

Planetary Surfaces”– Part 2: Angel Planet Assignment 4

Example of a proto-Planetary Disk

Objectives:

• Describe the significance of bombardment in the early solar system.

• Compare and contrast the structure & evolution of the terrestrial planets.

• Describe the differentiation into core, mantle & crust.

• Describe the heating and cooling processes in planetary interiors. Describe the importance of planetary size on its evolution.

Two Types of PlanetsTerrestrial:smallrocky, ironinner

Jovian:largeH, He, icesouter

When Planets Form - Bombardment & Differentiation

• Bombardment of planet as it forms, HEATS and melts its surface

• Molten iron and other heavy elements sink toward the center

• Falling iron converts gravitational potential energy to kinetic energy -> HEAT

Inside the Terrestrial Worlds

• After they have formed, the molten planets differentiate into three zones:• core - made of metals• mantle - made of dense rock• crust - made of less dense rock

• Lithosphere - the rigid, outer layer of crust & part of the mantle which does not deform easily

Inside the Terrestrial Worlds

Heating the Planets

• Planetary interiors heat up through:• accretion

• differentiation

• radioactivity

Supplies all the heat at the beginning

Supplies heat throughout the planet’s life

Cooling the Planets

• Planets Cool by Radiating Heat to Space from their Surface

• Heat is Transported from the Interior to the Surface by:• conduction - atoms & molecules moving &

hitting other atoms & molecules• convection - macroscopic flows: hot material

rising & cool material sinking

Convection

Cooling Terrestrial Planets

Role of Planetary SIZE

• Larger planets heat more– More iron to flow to center– More radioactive elements to split

• Larger planets cool slower– Extra layers provide extra insulation

Role of Planetary Size

• Heating proportional to Volume ~ R3

• Cooling proportional to Surface Area ~ R2

• Heating/Cooling ~ Volume/Area ~ R = Size

• Smaller Planets Cool Faster & Heat Less(by impacts and splitting of radioactive nuclei)-> Thicker rigid Lithosphere -> Less volcanism & Tectonic Activity

Inside the Terrestrial Worlds

active geology inactive geology

How do we Know about the Interior of Earth

• Earthquakes make waves

• Waves travel through Earth, the higher the density the faster the waves travel

• Two types of waves– Back & forth

– Side to side

Shaping Planetary Surfaces

• Major geological processes that shape planetary surfaces:• impact cratering: excavation of surface by asteroids or

comets striking the planet• volcanism: eruption of lava from interior• tectonics: disruption of lithosphere by internal stresses• erosion: wearing down by wind, water, ice

Counting Craters to find Surface Age • Cratering rate decreased as Solar Systems aged.

• The older the surface, the more craters are present.

Impact Craters - Mars

Volcanism - Mars Olympus Mons

Olympus Mons

Volcanism - Venus

Plate Tectonics

History of Plate Tectonics

• South America and Africa fit together like a jig-saw puzzle, with matching geological formations and fossils

• New Idea (Wegner 1912)Continental Drift

• Rejected by Geologists– Counter to established ideas– Lack of overwhelming evidence– No mechanism to drive motions

Evidence

Evidence

Mid-Atlantic Riftin Iceland

Division betweenNorth American& EuropeanPlates

Mechanism - Mantle Convection

Earth’s Plates

Earth’s Plate Motion

Valles Marinares - Mars

Erosion

Mars Evidence forwater in past

Erosion

Wind

Summary