CHAPTER 27: PLANETS OF THE
SOLAR SYSTEM
Section 27.1 – Formation of
the Solar System
 What exactly is a solar system
anyway?
 Consists of the Sun, all the planets,
and any other body that revolves
around the Sun
 And what exactly is a planet?
 Any primary bodies that orbit the
Sun (Earth, Venus, etc.)
 Where did it all come from?
Nebular Hypothesis
 1976, French mathematician
Pierre-Simon, marquis de
Laplace came up with
explanation for creation of
the solar system
 Sun and other planets came
together and condensed at the
same time out of a rotating
cloud of gas and dust
Solar Nebula
 Solar Nebula – the rotating cloud of gas and
dust from which the sun and planets formed
 Also any nebula from which stars and planets
(outside our solar system) may form
 99% of the material in
the Sun is matter that
was originally in the
solar nebula
Steps in the process
1.) Start with a solar nebula
(rotating cloud of gas and
dust)
2.) Contraction of gas and
dust into rotating disk
3.) Cooling causing
condensing into tiny (dust
sized) solid particles
4.) Collisions between these
form larger bodies
5.) The larger bodies
accrete (or build up) to form
planets
Let’s break it down into steps…
#1 Solar Nebula
•What “fuels” the nebula?
• Energy from collisions and pressure from gravity makes the center of
the nebula HOT and DENSE
• 99% of all the material in the nebula is in the sun
•Think back to our solar nebula activity! Where is most of the
material located?
Next Step…
#2 The nebula flattens as it rotates and gets warmer
near the center
•Starts to look like a disk
•Temperature begins to rise more at the center
•Think ice skater doing a spin!!
Third Step…
#3 Things begin to form
a. Planetsimals begin to form within the swirling disk
b. As they grow, gravitational pull increases and they continue
to grow more
•Planetesimals - “mini planets” or small bodies from which a
planet originated in the early stages at the beginning of the
solar system)
Fourth Step…
#4 Small planetesimals collide with larger ones
and the planets begin to grow
•As the planetesimals get bigger, their gravity
grows and they become protoplanets
•Protoplanets are
planetesimals that have
collided due to gravity
to form larger bodies
Fifth Step…
#5 The extra dust and gas is gradually removed from
the solar nebula by the collisions
•The removal of the other material leaves mainly just
planets around the sun and creates a new solar
system
Creation of Planets
• KEY THOUGHT: THE FEATURES OF A NEWLY
FORMED PLANET DEPEND ON THE DISTANCE
BETWEEN THE PROTOPLANET AND THE
DEVELOPING SUN
•IT ALL RELATES TO GRAVITY
• What has the most gravity in a solar system?
• THE SUN!
Inner vs. Outer Planets
 Inner protoplanets (which
are?) contained lots of
heavy elements
 Venus, Earth and Mercury
contain lots of nickel and iron
 These elements stuck
around because they
couldn’t be blown away or
evaporated by the Sun’s
heat and wind
More about inner planets
 As the inner planets formed, dense material
sank towards the middle of the planets and
lighter material stayed on top, forming layers
 Inner planets have solid surfaces (like Earth)
 Inner planets are smaller, rockier, and denser
than outer planets
Inner vs. Outer Planets
 Outer protoplanets (which are?) contained
lighter elements
 Jupiter, Saturn, Uranus, and Neptune contain
hydrogen, helium, and methane
 These planets are cold, have low densities, and
are HUGE
More on outer planets
 Outer planets known as “Gas Giants”
because:
 Mostly made of gases and are low density
 Jupiter’s density is only 24% of Earth’s but
Jupiter’s diameter is 11 times Earth’s
 Have liquid cores and gas outer layers
Pluto!
 Not considered an inner or outer planet
 Characteristics of Pluto
 Very small (smaller than Earth’s Moon!)
 Very COLD – it’s an ice ball made of frozen rock
and gas
More on Pluto
 Recently, scientists found many, many
objects in the universe that are similar to
Pluto beyond Neptune
 Because Pluto is more like these other common
objects rather than other planets, it is no longer
considered a PLANET.
Formation of Solid Earth
 3 sources of energy
contributed to the original
HOT temperatures on
Earth:
 Energy produced during
collisions with other
planetesimals
 Increased pressure on inner
layers of Earth from weight
of outer layers
 Radioactive materials were
abundant in Earth during its
formation
Early Solid Earth
 Differentiation – the process that occurred as
Earth developed where denser molten
materials sank to the center and less dense
materials were forced to the outer layers
3 Layers of Earth
 Core – the center of Earth
that is made of dense rocks
 Nickel and Iron most common
 Mantle – Earth’s thick
middle layer
 Iron and Magnesium-rich rock
 Crust – Outermost layer of
Earth
 Least dense material,
including silica-rich rocks
Present Solid Earth
 As time went on, Earth’s surface cooled enough for
solid rock to form
 While Earth already had distinct layers, the surface
continued to change from:
 Heat inside the Earth
 Impacts and interactions with the forming atmosphere
Formation of Earth’s Atmosphere
 Like the Earth’s interior,
the atmosphere formed
due to differentiation
 Hydrogen and helium
(lightest gases) rose to
surface of the Earth
 SO, the early atmosphere
was mostly made of H and
He
The Early Atmosphere
 Hydrogen and helium gas
are so light, Earth’s gravity
couldn’t hold them in for
long
 The Sun’s heat heated them
up and they blew away into
space
 Also, Earth’s magnetosphere
(protects our current
atmosphere) was possibly not
developed fully
OUTGASSING (no that’s not what
you think it is)
 The Earth’s surface
continued to evolve with
creation of volcanoes and
other land forms
 Volcanoes released
additional gases into
atmosphere:
 Water vapor, carbon dioxide,
nitrogen, methane, sulfur
dioxide, and ammonia
 What’s missing from this
list?????
More on outgassing
 Gases released from
volcanoes then
interacted with sun light
and heat
 Breakdown of ammonia
and water vapor into
OZONE (or three oxygen)
 Ozone is a shield against
UV rays of the Sun
The PRESENT Atmosphere
 Later, some plant life evolved that used
carbon dioxide from the atmosphere to
produce food (photosynthesis!)
 OXYGEN is the main product of photosynthesis
 About 2 billion years ago, the amount of oxygen in
the atmosphere increased a lot
 Composition of “air” is now stable
Oceans – Where did they come
from?
 Possibly from space!
 Some icy bodies (ex.
comets) collided with
Earth and added water
vapor to atmosphere
 As Earth cooled, water
vapor condensed to
liquid rain
 First ocean was probably
FRESH water
Why are oceans salty?
 Although first oceans were likely fresh, as
water flowed over land and rocks, it dissolved
minerals and salts carried them to the oceans
 After the water cycle was in place, the
concentration of salt in oceans increased
How did Oceans Affect
Atmosphere?
 Scientists believe the early atmosphere was
changed as oceans began to dissolve carbon
dioxide
 Current atmosphere likely has more carbon
dioxide than original atmosphere
 Earth’s early climate likely cooler than today
 Does CO2 in the atmosphere affect climate
today????
ASSIGNMENTS
 Outline Section 27.1 and Key Terms 27.1
 Due: