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Formation of the Solar System:
The Solar Nebular Theory
Video
Objectives
• Explain the nebular hypothesis of the origin of the solar
system
• Express the sequence of events that led to the
formation of our solar system
• Describe how the planets formed
The Basics
• Solar System: the sun and other celestial objects
gravitationally bound to it
• eight planets
• three dwarf planets (Pluto, Ceres, Eris)
• 165 known moons
• Planet: any body in orbit around the Sun which
• has enough mass to form itself into a spherical shape and
• has cleared its immediate neighborhood of all smaller objects.
• There are eight known planets in our solar system which meet
this qualification: Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus and Neptune.
A Bit of History
• Scientists have long debated the origins of the solar system.
• In the 1600s and 1700s, many scientists thought the sun formed first
and produced materials which later formed the planets. This was
incorrect.
• In 1796, French mathematician Pierre Simon, advanced a
hypothesis now known as the nebular hypothesis.
• Ummm yeah, what the heck is a nebular?
• A cloud is called nebula - so a nebular hypothesis is like a “cloud”
hypothesis
• The piece of cloud which formed our own solar system is called the
solar nebula
The Nebular Hypothesis
• About 4.6 billion years
ago ice, gas, and dust
(nebula/cloud) collapsed
under the weight of its
own gravity, began to
rotate, and eventually
formed our solar system
• The gases present were
primarily hydrogen and
helium
The Nebular Hypothesis
• The temperature
increased as the nebula
collapsed
• Rotation increased with
temperature
• Nebula eventually
flattened into a disk
• As the sun was forming in
the center of the nebula,
dust particles in the outer
regions combined to form
planetesimals a few km
across
Formation of Planets
• Planetesimal: a small body from which a planet
originated
• Eventually, the planetesimals formed into larger bodies
called protoplanets through accretion…
• Accretion is growing by colliding and sticking
• Protoplanets’ gravity attracted other planetesimals,
which added to their masses
• Eventually, they became very large and formed planets
and moons.
Evidence for Theory
•
The sun is composed of 99% of all matter which was contained in
the solar nebula.
•
All planets orbit the Sun, and rotate in the same direction. This
would be expected if they all formed from a disk of debris around
the Sun.
•
The planets are all composed of elements similar to that of our
Sun.
•
The planets are all in the same plane as the sun
•
Modern scientific calculations support this theory and help explain
how the sun and planets formed from an original nebula of gas
and dust.
Formation of the Planets
The diagram below shows the formation of the Solar
System..
The Solar System – Relative Sizes
of the Planets
Planetary Distances
•
•
•
•
•
•
•
•
•
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (planet?)
0.4 AU
0.7 AU
1.0 AU
1.5 AU
5.0 AU
10.0 AU
19.0 AU
30.0 AU
39.0 AU
• Light travels through
space at 300,000km/s.
• So it takes about 8
minutes for light from
the sun to travel 1 AU
and reach us.
• How long would it take
light from the sun to
reach Pluto?
• 39 x 8 = 312 minutes,
or 5.2 hours!
Inner Planets
Formation of Inner Planets
• The features of a newly formed planet depended on the
distance between it and the developing sun.
• The four closest to the sun became Mercury, Venus,
Earth, and Mars.
• These are smaller, rockier, and denser than the outer
planets. They contain large percentages of heavy
elements, such as iron and nickel.
• Lighter elements may have been blown away by
radiation and the solar wind from the sun. Planetary
gravity was not strong enough to retain their gases.
Outer Planets
Formation of the Outer Planets
• The next four planets are larger and became Jupiter,
Saturn, Uranus, and Neptune.
• These planets are referred to as Jovian or gas giants
because they are composed primarily of hydrogen
and helium.
•
Other characteristics include: low densities, rapid
rotation, deep atmospheres, rings and lots of
satellites.
Hey, What About Pluto?
•
Many scientists have declassified
Pluto from planetary status. They
do not believe it qualifies as a
major planet.
•
Pluto’s orbit is around our sun is
different than the other nine
planets, so astronomers have
always suspected it may be not
actually be a planet in our solar
system.
•
Recently, astronomers have
discovered hundreds of objects
similar to Pluto beyond Neptune’s
orbit. None of these objects are
larger than Pluto, but Pluto is
probably one of these objects.
•
Some scientists believe that Pluto
once was one of Neptune’s
moons, and that it pulled out away
from Neptune and made its own
orbit.
Just in Case Things Change
• Pluto, used to be the ninth
planet from the Sun, and the
smallest in our solar system.
• Pluto is the farthest planet from
the sun. It is the smallest of
known planets and is even
smaller than Earth’s moon.
• Pluto is very cold and may be
best described as an ice ball
made of frozen gases and
rocks.
Ways We’ve Studied the Solar
System
• Space Shuttle
• Space Missions
– Voyager
– Cassini
– Galileo
– Messenger
– Pathfinder
– Spirit and Opportunity
– Deep Impact
Rarely Seen
Shuttle Activity
NEAR Video
Mars Phoenix
Lander
Learning check
How is Pluto different from the other outer planets?
Reading check
How is Pluto different from the other outer planets?
Unlike the other outer planets, Pluto is very small and is
composed of rock and frozen gas, instead of thick layers
of gases.
Nebular Hypothesis Homework
• On a blank sheet of paper, write your name, date, and
period in the upper right hand corner
• On the top half of the page, sketch a series of diagrams
showing the nebular hypothesis (look at pages 686-687
of the book for help)
• On the bottom half, write a paragraph describing what
happened during the nebular hypothesis (use the
textbook and your notes for help)
• Due Tomorrow…Friday 1/18/2013