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Our Solar System
Chapter 28
Formation of the Solar System
28.1

Stars and planets form from interstellar
clouds




They appear dark because of dust blocking out
the light
The light can cause it to glow, or even become
heated
Starts and solar systems are “born” this way
Collapse accelerates

The collapse of this cloud is slow, but it
accelerates and becomes denser at the center


This collapse and spin results in a flattening at the
equatorial plane
Matter condenses


Our solar system may hav eformed this way when
temperature and pressure cause hydrogen to fuse into
helium
The temperature differential allowed for different
elements to concentrate in different areas around the
sun


This is why the inner planets are rocky and have a higher
melting point
Outer ones are less dense and made of ice and gas
 Much
like coalescence, the
planetesimals combined to get larger in
many cases to become the known
planets.
 Gas giants form
Jupiter was the first to form
 Icy planetesimals combined to form it
 Its mass (gravity) caused it to collect much of
the debris
 The others formed the same way, but Jupiter
took most of the extraneous material

 Terrestrial
planets form
the merging of planetesimals in the inner portion of
the disk
 Made of materials that resist vaporization
 Most of the gaseous material and “smaller stuff”
consumed by the sun, hence fewer satellites.

 Debris
All of the “junk” left over
 Some became comets
 Some ejected from solar system or destroyed in
collisions
 The asteroid belt between mars and Jupiter is the
rest

 Initially
the geocentric theory stated
that everything moved around the
earth.
 Retrograde motion led astronomers to
find a different explanation
 The heliocentric model (Copernicus)
put the sun at the center and planets in
orbit around it.
Proximity to the sun caused planets to move
at different speeds
 This explained retrograde

 Kepler’s
Laws
1st law is that planets move in elliptical orbits
 The sun was at 1 focus
 The semi-major axis (half the length of the major
axis) is where we get the AU (astronomical unit)
distance many distances are measured in


This is more math that I want to get into!
The eccentricity of the orbit is how “squashed” the
orbit is
 2nd law is an equal area is swept out in equal
amounts of time (although the orbital distance may
be different)
 3rd law he defined the size of the ellipse and the
orbital period (year)


Gravity is the attractive force between 2
objects

It is affected by mass and distance
Gravity is what determines the orbit planets
follow
 Newton’s explanation of gravity supported
Kepler’s laws of planetary motion.

The Inner Planets
28.2
10
 these
are the 4 inner planets
 similar densities to Earth
 solid rocky surfaces
11
 closest
to the sun
 1/3 Earth’s size
 no moons
 2 Mercury Years is 3 Mercury days
 Atmosphere


O2 and Sodium
replenished daily by the sun
12
 Surface



covered with craters and plains
the plains formed much like the maria on the moon
the craters are smaller with less ejecta
 Interior


the density suggests a dense core similar to the Earth
the magnetic field suggests its partially molten
13
 Has
no moons
 the brightest planet because of proximity
and albedo 75%
 Thick atmosphere doesn’t allow for direct
observation
 probes and satellites have provided radar
images of 98% of the surface
14
28.3
15
 These
planets include: Jupiter, Saturn,
Uranus and Neptune
 All larger than Earth by 15-300 times
16
 The
largest planet 1/10 of the sun and 11X
Earth’s
 Better than 70% of the planetary mass of the
solar system
 52% albedo
 Has a banded appearance
 “the great spot” is a storm that has lasted
for better than 300 years
17
 Density

is relatively low for its size
The is because of it composition (H and He in gas or
liquid form.
 Rotation

Shortest day in the solar system about 10hrs


This fast spin distorts the shape
This also contributes to its banded appearance
 Belts are low lying dark-colored clouds
 Zones are high light-colored clouds
 Moons

More than 60, but some are very small
18

Mostly composed of ice and rock
 Gravity
assist
19
 Second
largest planet in the solar system
 Atmosphere and interior


Slightly smaller than Jupiter
Density less than water… it would float!
 Rings



Much broader and brighter than other planets’
7 major rings made up of ringlets
Gravity keeps the rings in place
20
 Moons


55 moons
Titan, the largest is bigger than Mercury

Odd among moons because of content with dense atmosphere
and methane’s existence in 3 states
21
 4x
larger and 15Xmass of the Earth
 Atmosphere



Bluish appearance cause by methane gas
Clouds are similar in appearance to the surface
Liquid surface with a small solid core
 Moons

and Rings
At least 27 moons and faint rings
22

The rings are dark and almost not observed
 Rotation


Almost a top to bottom rotation
Poles vacillate between 42 years of darkness and light
23
 Atmosphere



Smaller and denser than Uranus but 4XEarth
Similar in color to Uranus (twins??) but does have some
color variation on surface
Belts and zones give it texture
 Moons

and Rings
13 moons Triton being the largest



Triton has retrograde orbit
Also has nitrogen geysers when heated by the sun
Rings are invisible from Earth but exist
24