Download Chapter 27 Formation of the Solar System

Chapter 27
Formation of the Solar System
The sun and all of the planets and other
bodies that revolve around the sun.
It all started with a Big Bang (theory).
The Nebular Hypothesis
* 1796 (Immanuel Kant)
• The sun and the planets condensed at about the same time
out of a collapsing cloud of gas and dust called a
solar nebula.
– About 4.6 billion years ago, the amount of gravity near one of these
clouds increased as a result of a nearby supernova (or some other
force).
– The rotating cloud of gas and dust from which the sun and planets
formed is called the solar nebula.
– Energy from collisions and pressure from gravity caused the center of
the solar nebula to become hotter and denser (10,000,000oC).
– Hydrogen fusion began… a star formed (we call ours the sun).
– The sun contains about 99% of all the matter contained in the solar
nebula.
– Planets started out as small bodies called
planetesimals.
– Some planetesimals joined together through
collisions and the force of gravity to form
protoplanets.
– Collisions added mass to the protoplanets to
become planets and some moons.
– the four inner planets are the terrestrial planets
of Mercury, Venus, Earth, and Mars.
– The four outer planets are the gas giants of
Jupiter, Saturn, Uranus, and Neptune.
Formation of solid Earth
• When Earth first formed, it was very hot.
(hot enough to melt iron)
– energy was produced when
• the planetesimals collided during formation
• The outer layers compressed the inner layers
• Radioactive materials present emitted high energy
particles.
• Heat caused denser materials to sink toward the center, a
process called differentiation, which led to the layers of the
earth (crust, mantle, and core).
• Earth’s surface cooled and solid rock at the surface formed.
Formation of Earth’s atmosphere
– Hydrogen and helium gas (less dense) rose to the
surface of the earth and were then released into the
atmosphere. They eventually escaped into space.
– As Earth’s surface continued to form, volcanic eruptions
were frequent and water vapor (H2O), carbon dioxide
(CO2), nitrogen (N2), methane, sulfur dioxide, and
ammonia were released.
– This outgassing formed the atmosphere.
– These gases reacted with radiation from the sun to
form other components such as ozone (O3).
– As life evolved, other gases, namely oxygen (O2), were
added to the atmosphere (2 billion years ago).
Formation of Earth’s Oceans.
• Some scientists think that, in addition to
outgassing, some of Earth’s water may have come
from space in the form of ice from comets.
• As Earth cooled, water vapor condensed to form
rain that collected on the surface.
• First it was all freshwater then later minerals such
as salt (halite) were washed and eroded in to it.
Aristotle’s Model
Geocentric Model of the Solar System
•
•
•
•
•
1st model of the solar system
Planets, stars and sun revolved around the earth.
Geocentric means “earth-centered”
Heavens are unchanging (perfect)
Theory lasted about 2000 years
• Problem:
– It did not explain how planets sometimes appear to move backwards
in the sky relative to the stars = retrograde motion.
Link
Ptolemy’s Model
• Greek philosopher –
proposed changes
• Planets moved in
small circles
(epicycles) as they
revolved around the
Earth.
• It actually explained
retrograde motion
pretty well.
Copernicus’ Heliocentric model
• 1543, polish astronomer Nicolaus Copernicus
• Heliocentric model of the Universe – “sun-centered”
• Planets revolve around the sun in the same direction
but at different speeds and distances from the sun.
• Explained retrograde motion the best
• Fast moving planets passed
slow moving planets which
made them appear to move
backwards.
Galileo Galilei
• Observed that four moons traveled around
the planet Jupiter.
• Showed him that objects can revolve around
other objects other than Earth.
Galileo Galilei
• Observed that mountains exist on
Earth’s moon.
• Showed him that objects don’t have to be
perfectly spherical and can be more like Earth
Kepler’s Laws #1
(based on observations by Tycho Brahe)
1. Law of ellipses
- each planet orbits the sun in a path called an ellipse
(oblong or oval, not a circle).
- eccentricity is the degree of elongation of an
elliptical orbit. The more eccentric the orbit the more
elongated it is.
(an eccentricity near “0” is almost a perfect circle).
Kepler’s Laws #2
(based on observations by Tycho Brahe)
2. Law of equal areas
– describes the speed at
which objects travel at
different points in their orbits.
- Objects move faster in their
orbit when they are closer
the sun.
- equal areas are covered in
equal amounts of time
as an object orbits the sun.
Kepler’s Laws #3
(based on observations by Tycho Brahe)
3. Law of periods
- describes the relationship between the average distance of a
planet from the sun and the orbital period of the planet.
- Orbital period is the time required for a body to complete a
single orbit (planets further away take longer to complete an orbit).
- allows Scientists to determine how far away a planet is from
the sun.
2
T
=
3
a
T = earth years and
Example: Jupiter’s orbital period is 11.9 Earth years (T),
the square is 142;
142 is 5.2 cubed
Jupiter is 5.2 AU from the sun.
a = AU
Newton’s laws of motion
• 1st Law: a moving body will remain in motion and resist a change
in motion until an outside force acts on it – inertia.
• Because a planet does not follow a straight path, an outside force
must cause the orbit to curve.
• Gravity! The gravitational pull of a larger object (sun) is that force.