SOL.SYS Lecture 4

Impact theory (Birth of Moon)

Moon was formed by giant impact between Mars-size object and earth ~4.5 billion years ago

Interior Structure of Moon

• Crust (top layer)

• Mantle (middle)

• Core (center)

Surface of Moon

• Craters

• Highlands

• Lowlands (Maria)

Craters (surface of moon)

• Crater sizes change from few meters to few hundred kilometers

• Most were formed by meteorite impact on moon

• Some are related to ancient volcanoes

Why are there so many Craters on Moon?

• No atmosphere to block impacting objects on moon

• No plate tectonics activities to destroy craters on moon

Highlands (surface of moon)

The bright areas of moon. Some are high mountains

Lowland (surface of moon)

• The dark parts of lunar landscape

• Originally were thought to be “oceans” (Maria in latin) by early astronomers

• Often filled by lavas on surface

Water Ice on Moon Surface

• During every rotation period, all surface is exposed to sun

• High daytime temperature melts solid ice and evaporates liquid water (it does not favor liquid water and solid ice on moon

• Some areas in lowlands and craters in polar regions can avoid sunlight permanently, water ice exist there

The Indian spacecraft (Chandrayann-1)

The spacecraft that provided evidence of water ice on moon

Where does water ice come from?

Comets

Moon near side

One side of moon always faces Earth. Relatively low topography and heavy elements

Moon far side

The other side of Moon’s near side. Relatively high topography and light elements

Disadvantages of Moon

• No atmosphere; no O2 for breathing, large cosmic ray and large temperature variations are bad

• Low gravity; not good for bone, losing calcium

• No liquid water; ice water is possibly used

Advantaged of Moon

• No moonquake (no tectonic activity on moon)

• Low gravity (easier to jump and build large structures)

• Good for astronomers (no atmosphere affecting telescopes)

Earth plates

The crust of earth is broken into few pieces. Boundaries of plates NOT always consistent with boundaries of oceans and continents

Types of plate movement:

• Convergent

• Divergent

• Transform

Seismic waves

• Earthquakes are sources of these waves

• Can help us understand/explore internal structure of earth

Types of Seismic Waves:

• Body waves

• Surface waves

Primary (P) Wave

Body wave analogous to sound

Secondary/Shear (S) Wave

Body wave analogous to light

Types of Surface Waves:

• Rayleigh wave

• Love wave

Rayleigh Wave

Analogous to ocean surface

Love Wave

analogous to snake or shaken rope. Little faster than Rayleigh wave

Volcano Mechanism

• in mantel, hot and melted rocks (magma) are buoyant. Can rise through crust to erupt on surface (same principle as hot air rising)

• Magma reaches crust, strength of eruption depends on how easily magma flows (viscosity) and amount of gas the magma has

Types of Volcanos:

• Shield

• Cinder cone

• Composite Volcano

Shield Volcano

• Can span across hundred of miles

• Flat compared to its horizontal extension

• Almost always have large craters

Cinder Cone Volcano

• Normally small about few miles span and about one thousand feet vertically

• Have fairly steep stopes and normally have small craters

Composite Volcano

• Differs from shield volcanoes by tall sides and much more explosive eruptions

Outer Core of Earth

• So hot that metals in it are all liquid state

• Composed of melted metals of nickel and iron

Inner Core of Earth

• In solid state because temperature and pressure so great there, metals are squeezed together and are not able to move like liquid

Magnetic Field of Earth

• In the outer core, liquid iron and nickel with electrons move with rotation of earth, the magnetic field is produced

• Solar winds change earth’s magnetic field from symmetric dipole to un-symmetric dipole