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Chapter 20 Touring Our Solar System

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Chapter 20

Touring Our Solar System

I. Overview of the solar system

A. Solar system includes

1. Sun

2. Nine planets and their satellites

3. Asteroids

4. Comets

5. Meteoroids


B. A planet’s orbit lies in an orbital plane

1. Similar to a flat sheet of paper

2. The orbital planes of the planets are inclined

a. Planes of seven planets lie within 3 " of the sun’s equator

b. Mercury’s is inclined 7 "

c. Pluto’s is inclined 17 "


C. Two groups of planets occur in the solar system

1. Terrestrial (Earthlike) planets

a. Mercury through Mars

b. Small, dense, rocky

c. Low escape velocities

2. Jovian (Jupiterlike) planets

a. Jupiter thorugh Neptune

b. Large, low density, gaseous

c. Massive

d. Thick atmosphere composed of

1. Hydrogen

2. Helium

3. Methane

4. Ammonia

e. High escape velocities

3. Pluto not included in either group


D. Planets are composed of

1. Gases

a. Hydrogen

b. Helium

2. Rocks

a. Silicate minerals

b. Metallic iron

3. Ices

a. Ammonia ( NH 3 )

b. Methane ( CH 4 )

c. Carbon dioxide ( CO 2 )

d. Water ( H 2 O )


II Evolution of the planets

A. Nebular hypothesis

1. Planets formed about 5 million years ago

2. Solar system condensed from a gaseous nebula


B. As the planets formed, the materials that composed them separated

1. Dense metallic elements ( iron and nickel ) sank toward their centers

2. Lighter elements ( silicate minerals, oxygen, hydrogen ) migrated toward their surfaces )

3. Process called chemical differentiation


III Earth’s moon

A General characteristics

1. Diameter of 2150 miles is unusually large compared to its parent planet

2. Density

a. 3.3 times that of water

b. Comparable to Earth’s crustal rocks

c. Perhaps the moon has a small iron core

3. Gravitational attraction is one-sixth of Earth’s

4. No atmosphere

5. Tectonics no longer active

6. Surface is bombarded by micro-meteorites from space which gradually makes the landscape smooth


B. Lunar surface

1. Two types of terrain

a. Maria ( singular, mare ), Latin for sea

1. Dark regions

2. Fairly smooth lowlands

3. Originated from asteroid impacts and lava flooding the surface

b. Highlands

1. Bright, densely cratered regions

2. Make up most of the moon

3. Make up all of the "back" side of the moon

4. Older than


2. Craters

a. Most obvious features of the lunar surface

b. Most are produced by an impact from a meteoroid which produces

1. Ejecta

2. Occasional rays (associated with younger craters)


3. Lunar regolith

a. Covers all lunar terrains

b. Gray, unconsolidated debris

c. Composed of

1. Igneous rocks

2. Breccia

3. Glass beads

4. Fine lunar dust

d. " Soil-like " layer

e. Produced by meteoric bombardment


C. Lunar history

1. New hypothesis suggest that a giant asteroid collided with Earth to produce the moon.

2. One method used to work out lunar history is to observe crater density

a. Older areas have a higher density

b. Younger areas are still smooth

3. Moon evolved in three phases

a. Original crust (highlands)

1. As moon formed, its outer shell melted, cooled, solidified, and became the highlands

2. About 4.5 billion years old

b. Formation of maria basins

1. Younger than highlands

2. Between 3.2 and 3.8 billion years old

c. Formation of rayed craters

1. Material ejected from craters is still visible

2. e.g., Copernicus (a rayed crater)

A. Mercury

1. Innermost planet

2. Smallest

3. No atmosphere

4. Cratered highlands

5. Vast, smooth terrains

6. Very dense

7. Revolves quickly

8. Rotates slowly

a. Cold nights ( -280 o F )

b. Hot days ( 800 o F )


B. Venus

1. Second to the moon in brilliance

2. Similar to Earth in

a. Size

b. Density

c. Location in the solar system

3. Shrouded in thick clouds

a. Impenetrable by visible light

b. Atmosphere is 97 % carbon dioxide

c. Surface atmospheric pressure is 90 times that of Earth’s

4. Surface

a. Mapped by radar

b. Features

1. 80 % of surface is subdued plains that are mantled by volcanic flows

2. Low density of impact craters

3. Tectonic deformation must have been active during the recent geological past

4. Thousands of volcanic structures


C. Mars

1. Called the " Red Planet "

2. Atmosphere

a. 1 % as dense as Earth’s

b. Primarily carbon dioxide

c. Cold polar temperatures ( -193 o F)

d. Polar caps of water ice, covered by a thin layer of frozen carbon dioxide

e. Extensive dust storms with winds up to 170 mph


3. Mar’s surface continued

a. Numerous large volcanoes -- largest is Mons Olympus

b. Less -- abundant impact craters

c. Tectonically dead

d. Several canyons

1. Some larger than Grand Canyon

2. Valles Marineras __ the largest canyon

a. Almost 5000 km long

b. Formed from huge faults


Mar’s surface continued

e. "Stream drainage" pattern

1. Found in some valleys

2. No surface water on the planet

3. Possible origins

a. Past rainfall

b. Surface material collapses as the subsurface ice melts

4. Moons

a. Two moons

1. Phobus

2. Deimos

b. Captured asteroids


D. Jupiter

1. Largest planet

2. Very massive

a. 2.5 more massive than combined mass of the planets, satellites, and asteroids

b. If it had been ten times larger, it would have been a small star

3. Rapid rotation

a. Slightly less than 10 hours

b. Slightly bulged equatorial region

4. Banded appearance

a. Multicolored

b. Bands are aligned parallel to Jupiter’s equator

c. Generated by wind systems


Jupiter continued

5. Great Red Spot

a. In planet’s southern hemisphere

b. Counterclockwise rotating cyclonic storm

6. Structure

a. Surface thought to be a gigantic ocean of liquid hydrogen

b. Halfway into the interior, pressure causes liquid metallic hydrogen

c. Perhaps rocky and metallic materials exists in a central core

7. Moons

a. At least 16 moons

b. Four largest moons

1. Discovered by Galileo

2. Called Galilean satellites

3. Each has its own character

a. Callisto

1. Outermost Galilean moon

2. Density cratered

b. Europa

1. Smallest Galilean moon

2. Icy surface

3. Many linear surface features

c. Ganymede

1. Largest Jovian satellite

2. Diverse terrains

3. Surface has numerous parallel

d. Io

1. Innermost Galilean moon

2. Volcanically active ( heat source could be from tidal energy )

3. Sulfurous

8. Ring system


E. Saturn

1. Similar to Jupiter in its

a. Atmosphere

b. Composition

c. Internal structure

2. Rings

a. Most prominent feature

b. Discovered by Galileo

c. Complex

d. Composed of small particles ( moonlets ) that orbit the planet


Saturn continued

3. Other features

a. Dynamic atmosphere

b. Large cyclonic storms similar to Jupiter’s Great Red Spot

c. At least 21 moons

d. Titan -- the largest Saturnian moon

1. Second largest moon ( after Jupiter’s Ganymede ) in the solar system

2. Has a substantial atomsphere

a. 80 % nitrogen

b. 6 % methane

c. Atmopsheric pressure is1.5 times Earth’s

3. May have polar ice caps


F. Uranus

1. Uranus and Neptune are considered twins

2. Rotates " on its side "

3. Rings

4. Large moons have varied terrains


G. Neptune

1. Dynamic atmosphere

a. One of the windiest places in the solar system

b. Great Dark Spot

c. White cirruslike clouds above the main cloud deck

2. Eight satellites

3. Triton - largest Neptune moon

a. Orbit is opposite the direction that all the planets travel

b. Lowest surface temperature in the solar system ( - 391 o F )

c. Thin atmosphere

d. Volcaniclike activity

e. Composed largely of water ice, covered with layers of solid nitrogen and methane


H. Pluto

1. Not visible with the unaided eye

2. Discovered in 1930

3. Highly elongated orbit causes it to occasionally travel inside the orbit of Neptune, where it currently is

4. Moon ( Charon ) discovered in 1978

5. Average temperature is - 210 degrees C

6. May have once been a moon of Neptune


V. Minor members of the solar system

A. Asteroids

1. Most lie between Mars and Jupiter

2. Small bodies - largest ( Ceres ) is about 620 miles in diameter

3. Some have very recent impacts

4. Many of the recent impacts on the moon and Earth were collisions with asteroids

5. Irregular shapes

6. Origin is uncertain


B. Comets

1. Often compared to large, " dirty snowballs "

2. Composition

a. Frozen gases

b. Rocky and metallic materials

3. Frozen gases vaporize when near the sun

a. Produces a glowing head called the coma

b. Some may develop a tail that points away from the sun due to

1. Radiation pressure and

2. Solar wind


Comet’s continued

4. Origin

a. Not well known

b. Form at great distance from the sun

5. Most famous short-period comet is Halley’s comet

a. 76 - year orbit period

b. Potato-shaped nucleus ( 16 km by 8 km )


C. Meteoroids

1. Called meteors when they enter Earth’s atmosphere

2. A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet’s path

3. Meteoroids are referred to as meteorites when they are found on Earth


Meteoroids continued

a. Types of meteorites classified by their composition

1. Irons

a. Mostly iron

b. 5 - 20 percent nickel

2. Stony

a. Silicate minerals

b. Inclusions of other minerals

3. Stony-irons -- mixtures

4. Carbonaceous chondrites

a. Rare

b. Composition

1. Simple amino acids

2. Other organic material

b. May give an idea as to the composition of Earth’s core

c. Give an idea as to the age of the solar system

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