The Beginning of Our Solar System

Ch 27

Questions??What are some theories about how our solar

system began?

The Nebular Hypothesissolar nebular a rotating cloud of gas and

dust from which the sun and planets formed

In 1796, French mathematician Pierre Simon, advanced a hypothesis now known as the nebular hypothesis.

The Nebular HypothesisThe sun is composed of about 99% of all of the

matter that was contained in the solar nebula.planetesimal a small body from which a planet

originated in the early stages of development of the solar system

Nebular HypothesisSome planetesimals joined together through

collisions and through the force of gravity to form larger bodies called protoplanets.

Protoplanets’ gravity attracted other planetesimals, collided, and added their masses to the protoplanets

Diagram of Nebular Hypothesis

Nebular HypothesisStep 1:

The young solar nebula starts to collapse due to gravity.

Step 2:As it rotates, it flattens and becomes warmer

near the center…this is where our sun formed.Step 3:

Planetesimals form within the swirling disk

Nebular HypothesisStep 4:

As planetesimals grow, their gravitational pull increases. Larger planets collect mostly dust and gas.

Step 5:Small planetesimals hit larger ones and planets

begin to grow.Step 6:

Left over dust and gas leave solar nebula and our solar system is formed!

The PlanetsThe Inner Planets:Mercury, Venus, Earth, Mars

Smaller, rockier, more dense than outer planetsContain heavier elements like nickel and iron

The outer Planets:Jupiter, Saturn, Uranus and Neptune

Composed of lighter elements such as helium, hydrogen and their ices (water ice, ammonia ice & methane ice)

Called gas giants b/c made of gas and have low density

Pluto – The Different Planet

Farthest and smallest planet (smaller than Earth’s moon)Ice ball made of frozen gasses and rocksScientist do not believe that Pluto qualifies as a real

planet.Question?? How is Pluto different from the 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.

The Formation of Solid Earth

First, Earth was very hot, then Earth cooled to form three distinct layers.

Differentiation – denser materials sank to the center and lighter materials were forced to the outer layers.Center: dense core of iron and nickelMantel: surrounds core, think layer of iron &

magnesium rich rockCrust: outermost layer, less dense, silica rich

rock

Earth’s Layers

Earth’s AtmosphereThe atmosphere formed because of

differentiation.Earth’s gravity is too weak to hold high

concentrations of hydrogen and helium gases and is blown away by solar winds.

OutgassingOutgassing formed a new atmosphere as

volcanic eruptions released large amounts of gases

The ozone formed from remaining oxygen molecules after solar radiation caused ammonia and some water vapor to break down.

Formation of Earth

Outgassing

Earth’s Present AtmosphereThe ozone collected in a high atmospheric layer

around Earth and shielded Earth’s surface from the harmful ultraviolet radiation of the sun.

Organisms, such as cyanobacteria and early green plants, could survive in Earth’s early atmosphere by using carbon dioxide during photosynthesis

These organisms produced oxygen as a byproduct of photosynthesis and helped slowly increase the amount of oxygen in the atmosphere.

Question??

How did green plants contribute to Earth’s present-day atmosphere?Green plants release free oxygen as part of

photosynthesis, which caused the concentration of oxygen gas in the atmosphere to gradually increase.

Formation of Earth’s OceansWere the first oceans fresh water or salt

water?Fresh water

As rain continued to fall, rocks were dissolved into the oceans.

As evaporation occurred, some of the chemicals from the rocks combined to form salts, making the oceans increasingly more salty.

The Ocean’s Effect on the Atmosphere

The ocean affects global temperature by dissolving carbon dioxide from the atmosphere.

Since Earth’s early atmosphere contained less carbon dioxide than today, Earth’s early climate was probably cooler than the global climate is today.

Multiple Choice1. Small bodies that join to form protoplanets

in the early stages of the development of the solar system are

A. planets

B. solar nebulas

C. plantesimals

D. gas giants

Chapter 27

Multiple Choice, continued1. Small bodies that join to form protoplanets

in the early stages of the development of the solar system are

A. planets

B. solar nebulas

C. plantesimals

D. gas giants

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Multiple Choice, continued2. Scientists hypothesize that Earth’s first

oceans were made of fresh water. How did oceans obtain fresh water?

A. Water vapor in the early atmosphere cooled and fell to Earth as rain.

B. Frozen comets that fell to Earth melted as they traveled through the atmosphere.

C. As soon as icecaps formed, they melted because Earth was still very hot.

D. Early terrestrial organisms exhaled water vapor, which condensed to form fresh water.

Chapter 27

Multiple Choice, continued2. Scientists hypothesize that Earth’s first

oceans were made of fresh water. How did oceans obtain fresh water?

A. Water vapor in the early atmosphere cooled and fell to Earth as rain.

B. Frozen comets that fell to Earth melted as they traveled through the atmosphere.

C. As soon as icecaps formed, they melted because Earth was still very hot.

D. Early terrestrial organisms exhaled water vapor, which condensed to form fresh water.

Chapter 27

Multiple Choice, continued3. The original atmosphere of Earth consisted

of

A. nitrogen and oxygen gasesB. helium and hydrogen gasesC. ozone and ammonia gasesD. oxygen and carbon dioxide gases

Chapter 27

Multiple Choice, continued3. The original atmosphere of Earth consisted

of

A. nitrogen and oxygen gasesB. helium and hydrogen gasesC. ozone and ammonia gasesD. oxygen and carbon dioxide gases

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Multiple Choice, continued4. Scientists think that the core of Earth is

made of molten

F. iron and nickelG. nickel and magnesiumH. silicon and nickelI. iron and silicon

Chapter 27

Multiple Choice, continued4. Scientists think that the core of Earth is

made of molten

F. iron and nickelG. nickel and magnesiumH. silicon and nickelI. iron and silicon

Chapter 27

Short Response6. What four planets make up the group known

as the inner planets?

Chapter 27

Early Models of the Solar SystemGeocentric = ?

Earth centered solar system Aristotle proposed this idea Sun, stars and planets

revolved around the Earth

Claudius PtolemyProposed changes to Aristotle’s modelThought that planets moved in small circles,

called epicycles, as they revolved around the Earth.

Explained why some planets seemed to move backwards at times: retrograde motion.

The word ”retrograde” derives from the Latin words “retro” meaning backwards, and “gradus”, meaning step

A circular orbit in a circular orbit.

This satisfied the Greek’s idea of an Earth centered Universe and the idea that the motion of the heavenly bodies moved in perfect circles.

Early Models of the Solar SystemHeliocentric = ?Sun centered solar system

Copernicus proposed this ideaPlanets revolved around the sun but at different speeds and distances from the sun.

Kepler’s LawsLaw of Ellipseseccentricity - the degree of elongation of an elliptical orbit

(symbol, e)The law of ellipses states that each planet

orbits the sun in a path called an ellipse, not in a circle.

Kepler’s LawsLaw of Equal Areas

The law of equal areas describes the speed at which objects travel at different points in their orbit. It states that equal areas are covered in equal amounts of time as an object orbits the sun.

When the object is near the sun, it moves relatively rapidly. When the object is far from the sun, it moves relatively slowly.

Law of Equal Areas

Kepler’s LawsLaw of Periods

orbital period - the time required for a body to complete a single orbit

The law of periods describes the relationship between the average distance of a planet from the sun and the orbital period of the planet

Kepler’s Third LawThe mathematical equation, K x a3 = p2,

where K is a constant, describes this relationship.

When distance is measured in astronomical units (AU) and the period is measured in Earth years, K = 1 and a3 = p2.

a = average distance from the sunp = period

Example:Jupiter has an orbital period of 11.9 Earth

years.Find the average distance.

a³ = p²

a³ = (11.9)²a³ = 142

a = 5.2 AU

Kepler’s Laws explained by Newton:inertia the tendency of an object to resist being

moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object

Who discovered gravity?Newton

Gravity - an attractive force that exists between any two objects in the universe.

While gravity pulls an object towards the sun, inertia keeps the object moving forward in a straight line. This forms the ellipse of a stable orbit.

The gravitational pull is strongest closer to the sun, and weakest further from the sun.

Law of Inertia:

QUIZ!!!!!1. A planet moves relatively slower when it is

farther from the sun than it does when it is closer to the sun.

True or False?

True

QUIZ!!!1. Kepler’s first law states that each planet

orbits the sun, not in a circle, but in an ellipse.

True or False??

True

QUIZ!!!1. Kepler’s third law states that the square of

the average distance of a planet from the sun is proportional to the cube of the orbital period.

True of False

False