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Chapter 13
The Solar System
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 “Give
thanks to the Lord, for
he is good.
… who made
the great lights – the sun to
govern the day, the moon and
stars to govern the night; …”
Psalms 136:1, 7-9
Planets, moons and other
bodies

Our Solar System
 Sun
 8 planets ?
 ~100 moons
 Thousands of asteroids, millions of
icy bodies, comets, …
Planets, moons and other bodies

Astronomical unit (AU)
Average Earth-Sun distance
 1.5x108 km
 1 km = 0.621 mile or 3280.8 feet
 @ 93 million miles

 (92,900,836.17

mi or 149,589,777 km)
Light –year (lt-yr) is used for longer distances
 How
far light travels in one solar year
 Speed of light = 186,282,3976 miles per second
 5,880,000,000,000mi or 63,240 AUs !!!

Planet classification:
size
 density
 atmosphere


Two main divisions
Planets, moons and other bodies
 1.
FourTerrestrial planets - mostly
rocky material, metallic nickel and
iron
 Mercury
 Venus
 Earth
 Mars
Planets, moons and other bodies

2. Four Giant Gas Planets - mostly hydrogen,
helium and methane
 Jupiter
 Saturn
 Uranus
 Neptune
 Pluto
is now considered a dwarf planet
The order of the planets
Mercury






Innermost planet
2,439.7 km radius
Highly elliptical orbit
Average distance ~
0.4 AU (36 million
miles)
Orbital period (year) ~
88 days
Sun rise to sun rise
(“day”) ~ 176 days
Mercury
Visible shortly
after sunset or
before sunrise
No atmosphere;
No moon
40% smaller than Earth
 Day hot enough to melt metal 427 C
 Night cold as liquid nitrogen -173 C
 Mariner 10 flew past Mercury in 1974
 Magnetic field
 Craters like our moon
 Cliffs hundreds of kilometers high and long
 Plains of smooth lava

Planets, moons and other bodies
12
Venus





Orbital distance ~ 0.7
AU (67 Million miles)
Morning and evening
“star”
Exhibits phases, like
the Moon
No moons
Rotational motion
opposite orbital
motion
Venus
Venusian “day” longer than Venusian
“year”
 Visited by numerous probes
 Mostly CO2 atmosphere, high temperature
and pressure
 Surface mostly flat but varied

Venus
 3rd
brightest in
sky
 Called the sister
planet of earth
 nearly same
size and
weight
Venus

Actually hotter than Mercury (900O F)

“Greenhouse” effect
Clouds of sulfur and CO2
 462 C surface temperature
 Besides “morning star” known as:

“witch star”
 “dragon star”

“nearest you can get to hell”
(Russian Probe lasted less than an hour)
Earth’s Moon






1/6th gravity of earth
no atmosphere
one orbit takes 27
days
238,857 miles from
earth
never see dark side
12 Apollo astronauts
have walked on the
moon (1969-1972)
footsteps still there
Earth’s Moon

Lunar highlands
Light colored
mountainous
regions
 craters
 Breccias - rock
fragments
compacted from
meteorite impact

Earth’s Moon

Maria (“sea”)
Smooth dark areas formed from floods of
lava
 Basalt - similar to rock formed from cooling
lava on earth
 Formed about 3.1 – 3.8 billion years ago


Surface

3 meters grey dust containing microscopic
glass beads formed by bombardment of
meteorites
Moon Rocks


Glass
840 pounds brought
back
Stages in Formation of the Moon

Origin Stage

Moon formed from impact of Earth with very
large object, perhaps as large as Mars. The
moon formed from ejected material
produced by collision
Stages in Formation of the Moon

Molten Surface Stage
First 200 million years
 Lunar surface melted due to rock impact
 Fewer bombardments, moon surface
solidified
 Craters: result of meteorite impact after
formation of crust

Stages in Formation of the Moon

Molten Interior Stage
3.8 billion years ago
 Interior melted due to heat generated by
radioactivity


Cold and Quiet Stage
3.1 billion years ago
 Last lava solidified
 Little surface change since

Lunar Eclipse
Mars – the Red Planet
Mars

Orbital distance ~






1.5 AU (141 million mi)
One year is 687 days
One day is 24 hrs and
37 minutes
½ the size of earth
Numerous space
probes
2 moons


Deimos
Phobos
Mar’s Moons
Mars

Geologically active
regions:
Inactive volcanoes
Canyons
 Terraced plateaus
 Flat regions pitted
with craters

Mars




Thin atmosphere,
95% CO2--freezes at
the south pole
Strong evidence for
liquid water in past
Olympus Mons is 16
miles high
dust storms
Mars Spacecraft
Reconnaissance Orbiter (2004)
Spirit and Opportunity
Mars Exploration Rovers


Found that Mars
made of basalt
rock and
groundwater that is
dilute sulfuric acid
Confirmed
sufficient amounts
of water have been
present in the past
Spirit Rover
Spirit
ExoMars
2015
Earth
and
Moon
from
Mars
Jupiter
Jupiter

~ 5 AU from Sun




One orbit is 12 EY
Day is 10 hours
Most massive planet


483 million miles
318 times Earth’s
mass
200 pound man
would weigh 500
pounds
Jupiter
4th brightest object
in sky
 Mostly H, He &
iron-silicate core
 “Dynamic”
atmosphere



H2, He, ammonia,
methane, water,
Rings are present
Jupiter

Great Red Spot
permanent
“hurricane”
 2-3 Earths
could fit inside
spot

Jupiter’s Moons
39 widely varying
satellites (moons)
 Galilean moons:
 Io (active
volcanos)
 Europa
 Ganymede
 Callisto

1994 Shoemaker-Levy Comet
hits Jupiter
Saturn
Saturn

9.5 AU from Sun







886.2 million miles
10 hr day
29 1/2 years to orbit Sun
Second largest planet
10 times larger than earth
Many rings made of ice
and rocks
Mainly hydrogen and
helium
Surface similar to Jupiter’s
 Very cold -285 F
 Surface has dark and light bands
 Rapid Rotation causes the equator to
bulge
 Lowest Density = 0.7 that of water (float)

Saturn

30 satellites
 Titan: Largest
(Mercury) only
moon in solar
system with
substantial
atmosphere
(nitrogen)
Uranus
Uranus







Uranus (~19 AU)
3rd largest planet
84 year orbit
16 hour day
27 moons
Rings present
1/400th sunlight earth
receives
Uranus’ Five Major Satellites
Neptune

Neptune: Blue Planet
(~30 AU) 3 billion km
165 years to orbit Sun
Great Dark Spot

Turbulent atmosphere

Very cold surface of
frozen hydrogen and
helium

13 moons



Triton largest moon
Pluto
Pluto:
Smaller than the
Moon
70% rock; 30%
water ice;
thin atmosphere
Unusual orbit
Tilted 17o from
ecliptic
Crosses
Neptune’s
Smaller bodies of the Solar System
Comets, asteroids,
meteorites
 Leftover from solar
and planetary
formation
 Mass of smaller
bodies may be 2/3
of total Solar
System mass
 Bombard larger
objects

Comet structure


Small, solid
objects
“Dirty snowball”
model
 Frozen water,
CO2, ammonia,
and methane
 Dusty and rocky
bits
Comet structure

Comet head


Solid nucleus and coma of gas
Two types of tails
1. Ionized
gases
2. Dust

Tail points away from Sun
Asteroids


Located in belt
between Mars and
Jupiter
Sizes: up to 1,000 km
Asteroids

Varied composition
Inner belt: stony
 Outer belt: dark with carbon
 Others: iron and nickel

Formed from original solar nebula
 Prevented from clumping by Jupiter
nearby

Meteors and meteorites

Meteoroids
 Remnants
of
comets and
asteroids
Meteors and meteorites
Meteor
 Meteoroid encountering Earth’s
atmosphere
 Meteor showers: Earth passing through
comet’s tail
 Meteorite
 Meteoroid surviving to strike Earth’s
surface

Origin of the Solar System
Protoplanet nebular
model
 Stage A


Formation of heavy
elements in many
earlier stars and
supernovas
Concentration in one
region of space as
dust, gas and
chemical compounds
Origin of the Solar System

Stage B
 Formation of large,
rotating nebula
 Gravitational
contraction, spin
rate increases
Origin of the Solar System

Most mass concentrates in central protostar

Remaining material forms accretion disk

Material in accretion disk begins clumping
Origin of the Solar System

Stage C


Solar ignition flare-up
may have blown away
hydrogen and helium
atmospheres of inner
planets
Protosun becomes a
star
Origin of the Solar System

Protoplanets heated, separating heavy and
light minerals

Larger bodies cooled slower, with heavy
materials settling over longer times into
central cores