Terrestrial Planets


Click on the graphics for larger version.  For a printer friendly version, click here.

A) Mercury

1) Named after the Roman messenger of the Gods

2) Intermediate in size

3) Close orbit to sun

(a) Hard to see

4) Cratered similarly to the moon

(a) Caloris Basin

(b) Weird terrain

5) No atmosphere

6) Temperature fluctuations

(a) -170º C - 430º C

(b) Not the hottest

7) Made mostly of iron

(a) Indicates very large hit

(b) Dislodged other material

8) Rotates once on axis one and half times for each orbit around the sun

(a) 3 days every 2 years

(b) Very elliptical


Weird Terrain

Fault Lines

Caloris Basin

B) Venus (for an animation of Venus's rotation, click here.)

1) Name after the Roman goddess of love

2) Planet closest in size to Earth

3) Shrouded in deep layer of clouds

(a) Easily seen due to reflection of light off clouds

(1) Third brightest object after Sun and moon

4) Surface is similar to biblical notion of Hell

(a) Hot - 475º C

(b) Air pressure 100 times of Earth

(c) Rains sulfuric acid

(d) Atmosphere of carbon dioxide

(1) Greenhouse effect

(e) Volcanic eruptions

(f) Outer mantle may melt occasionally

(g) Surface

(1) 65% rolling plains

(2) 25% highlands

(i) Ishtar – Babylonian goddess of love

(ii) Aphrodite – Greek goddess of love

(3) 10% volcanoes

(i) no evidence of plate tectonics

(ii) currents in mantle form bulges – coronae

1. Maxwell Monte – twice the size of Mount Everest

(h) One of 2 planets to spins in a clockwise direction (Uranus)

(1) Slowest rotating planet

(2) Impact with large object

Surface of Venus - Magellan Mission
Impact Craters Evidence of Volcanic Activity

C) Earth

1) Formed in the inner solar nebula

2) Four stages of planetary development

(a) Differentiation

(1) Molten

(i) Matter separated due to density

1. Iron sank to core

2. Lighter silicates floated to surface and formed the crust

(b) Cratering

(1) Solid surface is bombarded with debris from solar system

(c) Flooding

(1) Radioactive decay heats planets interior

(2) Lava rises and floods basins

(3) Planet cools, water falls as rain and collects to form oceans

(d) Surface evolution

(1) Plate tectonics and erosion change surface features slowly

3) Interior

(a) Differentiated

(1) Density of Earth is 5.52 g/cm3

(i) Crust is much less dense

(ii) Hence interior is made of heavier elements

(2) Four areas

(i) Crust

1. Very thin – 35 – 60 Km deep

2. Thinner than skin of an apple

3. Density of 3.0 g/cm3

(ii) Mantle

1. Layer of dense rock

a. Hot and high pressure

b. Malleable

c. Denser than crust

d. Mantle movement cause crust to move and produces earthquakes

2. Density of 4.4 g/cm3

(iii) Liquid Core

1. Plate tectonics

2. Explored by monitoring shock waves from earthquakes

a. S Waves – shaking waves

i. Travels only through solids

b. P Waves – pressure waves

i. Travels through all materials

ii. Felt on opposite side of Earth during earthquake - hence core is liquid

3. Made of molten iron and nickel

4. Density of 14.0 g/cm3

(iv) Solid Core

1. Pressure so great, iron and nickel become solid

4) Atmosphere

(a) Secondary - Not original

(b) Primeval Atmosphere

(1) rich in carbon dioxide, nitrogen and water vapor

(2) during flooding stage, carbon dioxide dissolved into Earth’s ocean and formed into carbonate rocks

(3) oxygen released by green plants

Earth's Surface from Space

North and South America Rocky Mountains

Colorado River & Grand Canyon USA at nightfall
Differentiation Earth's Interior Earth's Crust

Fossil Evidence

for Plate Tectonics

Ring of Fire Plate Boundaries Plate Motion Formation of Atmosphere
Oxygen Production Earth's Atmosphere

D) Moon

1) Unique in size relationship to Earth – very large

2) Origin of moon

(a) Capture Theory

(1) Captured by gravitational field of Earth

(2) Does not explain why moon orbits Earth in same plane as Earth orbits Sun

(b) Twin Theory

(1) Formed alongside of Earth

(2) Earth and moon should be made of same substances

(i) Not true

(c) Impact Theory

(1) Early Earth impacted by large object size of Mercury

(2) Jettisoned large amount of exterior material

(i) Explains why moon is made of mostly lighter material

(ii) Size

(3) Most widely accepted theory

3) Notable surface features

(a) Craters

(1) Indicates no atmosphere

(2) Not tectonically active

(3) Named after scientists

(b) Maria

(1) Dark regions

(2) Newer, heavier material

(i) Congealed lava pools created by impacts

(3) Seas

(i) Sea of Tranquility

(ii) Sea of Storms

(c) Highlands

(1) Light areas

(2) Made of anorthsite

(i) Lighter, old form of rock

4) Eclipses

(a) Lunar

(1) Earth casts its shadow on moon

(b) Solar

(1) Moon casts its shadow on Earth

(c) Occur about two weeks apart

(1) Do not happen monthly due to 5º difference in plane

5) Orbit

(a) Orbits Earth every 27.32 days (Sideral Period – reference to the stars)

(b) Actual phases take 29.5 days to complete due to Earth rotation (Synodic Period – reference to the Sun)

(1) New

(2) Waxing Crescent

(3) First Quarter

(4) Waxing Gibbous

(5) Full

(6) Waning Gibbous

(7) Third Quarter

(8) Waning Crescent

6) Tides

(a) Moon’s gravity pulls on Earth causing bulge of water

(b) Earths spinning causes the tides

(c) Two high tides and two low tides each day

(1) Spring tides – Moon and Sun together

(2) Neap tides – Moon and Sun opposite

The Moon and it's interior Solar Eclipse
Lunar Eclipse Spring and Neap Tides Tidal Bulge Moon's Forces

E) Mars

1) Named after Roman god of War

(a) Red planet due to large amount of oxidized iron on surface

2) Half size of Earth

(a) Similar rotational period

(b) Orbit is twice Earth’s

3) Atmosphere

(a) Similar to Venus

(1) Thinner

(2) Cannot hold light gases due to low gravity

(i) No greenhouse effect

(3) Ice caps

(i) Frozen water and carbon dioxide

4) Surface

(a) Dried out water channels

(1) Evidence of water

(2) Lack of ozone layer contributed to water molecules being broken down to hydrogen and oxygen and then being released into space due to low gravitational field

(3) Water may be in form of permafrost below surface

(b) Thick outer crust

(1) Largest volcano in Solar System

(i) Olympus Mons

1. Base size of the state of Missouri

2. Twice the height of tallest volcano on Earth

(2) Tharsis

(i) Bulge formed 10 km above

(3) Valles Marineris

(i) Named after the Mariner Space Probe that discovered this

(ii) Would reach from New York to Los Angeles

(iii) Over 4 miles deep in places

(iv) Thought to be a casual relationship with Tharsis

5) Two moons

(a) Phobos – fear

(b) Deimos – panic

Mar's Surface Olympus Mons
Tharsis Montes Elysium Mons Deimos Phobos
Comparison of Olympus Mons and Earth Features

Astronomy  >        <  Website Directory  >