Our Solar System

Chapters 26, 27, and 28

What are Planetary Systems?

• A star with orbiting planets• Natural by-product of formation of starsWhy do you think they are a natural by-

product?If natural by-product, why don’t astronomers

know of more planets?• Planets are hard to discover because they

give off no light of their own

How did our Solar System Form?• Formed from same nebula that created

our sun• Mostly hydrogen and helium, but had

smaller amounts of carbon, nickel, iron, aluminum, and silicon.

• Cloud spun around and flattened.• Clumps began to collide and condense

forming small clumps (planetary seeds)

Nebular Theory

Nebular Theory1. Solar System formed from rotating

cloud of dust and gas.2. Sun formed at center

• (4.6 billion years ago)3. Small debris (planetesimals) collided

eventually gaining enough mass to become the planets.

4. Heavier materials combined closer to the sun to form the terrestrial planets.

5. Lighter materials combined further out to form the gas giants

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How do Scientists determine the age of the Solar System?

• Use evidence from meteorites, moon rocks, and Earth rocks

• Radiometric Dating shows oldest meteorites formed more than 4.54 billion years ago (bya).

• Moon rocks also date to 4.5 bya.• Infer solar system must have formed a

bit earlier (4.6 bya)

Remembering our Sun…

Remembering our Sun…• What type of reaction produces its energy?• Nuclear Fusion (Hydrogen atoms combine to

form Helium) (occurs in the core.)• What holds the sun together during this reaction?• Gravitational Forces pulling the atoms

inward• What type of star is the sun considered to be?• Main-Sequence, medium sized star.• What will be the remaining life cycle of our sun?• Become Red Giant (burning Helium) then

turn into a white dwarf leaving a nebula cloud of gas behind

Proximity of Planets and Stars

• Is Earth closer to other planets or other stars?

• Planets are much closer than stars.• What evidence do we have to suggest

this?• Parallax Angles• Only under gravitational pull of sun,

not other stars.

• Nearest objects have the largest Parallax angle, while distant objects are too small to measure.

Our Solar System• 99.85% of mass contained within the sun• Planets make up most of remaining .15%• What else is in our solar system?• Moons (Planetary Satellites), Dwarf

Planets, Asteroids, and other smaller bodies

• Terrestrial Planets = small and rocky• Jovian Planets = Huge, gas giants.• Size is most obvious difference• Density, chemical make-up, and rate

of rotation are also ways to distinguish them.

Terrestrial Planets

• Mercury, Venus, Earth, Mars• Formed in the warmer inner regions

of the disk• Heat drove off lighter elements, so

these planets were composed of heavier elements (metals and rock).

• Small planets and couldn’t attract hydrogen and helium.

Gas Planets

• Jupiter, Saturn, Uranus, Neptune• Outer regions were rich in icy, lighter

elements. • They grew large and could capture

hydrogen and helium in their gravitational force

• Became gas planets rich in hydrogen and helium with dense, frozen cores.

Atmospheres of Planets• Depends on mass and temperature of planet• Planets must be massive enough for gravity

to hold in gases to form an atmosphere.

Jovian (Gas Giants) Terrestrial

•Thick Atmospheres•Hydrogen, Helium, Methane, Ammonia

•Meager atmospheres

Mercury

• Innermost Planet• Slightly larger than

our Moon• Very dense• Large Iron core• 59 earth days for one

rotation• Greatest Temperature

Extremes (-173oC to 427oC)

Venus• Veiled Planet• Covered in Thick

Clouds• Similar to Earth in

size, density, mass, and location.

• Volcanism and tectonic activity shape Venus’s surface

• Greenhouse Effect (atmosphere is 97% CO2)

Earth

• Distance from sun allow water to exist in all three phases: solid, liquid, and gas

• Allows possibility of life.

• Atmosphere 78% Nitrogen, 21% Oxygen, mild green house effect support life.

Mars

• The Red Planet• White Polar Caps• Easy to observe• Thin Atmosphere• Extensive, hurricane-

force dust storms• Didn’t have enough

gravity to keep its atmosphere

Jupiter• 2 ½ more massive than

all other planets and moons combined!

• Most rapid rotation (10 hours)

• Great Red Spot• Surface likely and

“ocean” of liquid hydrogen

Saturn• 2nd largest planet• Ring System

composed of ice and rock

• Active Winds (up to 1500 km/hr)

• Large cyclonic “storms”

Uranus

• The Sideways Planet• Axis of rotation is

parallel with the planet’s orbit

• Contains ring system like all gas giants

• 4x as large, and 15x as massive as Earth

• Blue, velvety appearance

Neptune• The Windy Planet

(exceed 1000 km/hr)• Great Dark Spot• Very similar to Uranus

in size and mass

Minor Members of our Solar System:

• Asteroids• Meteoroids• Comets

Asteroids (Microplanets)• Small Rocky Bodies• “Flying Mountains”• Most orbit between

orbits of Mars and Jupiter in the Asteroid Belt

• Occasionally collide and fragments break off

Meteoroids• Small solid particle• Meteors enter Earth’s

atmosphere and burn up (shooting stars)

• Meteorites actually reach Earth’s surface

Originate from the following sources:

1. Interplanetary debris.2. Material from the

asteroid belt.3. Solid remains of

comets.

Comets• Rocky/Metallic

materials held together by frozen gases

• Travel in elongated orbits.

• As approach sun, solar energy vaporize frozen gases which produces glowing head (coma)

• As travel away from sun, gases refreeze.

Formation of an Impact Crater

Effects of Meteoroid Impacts…

Effects of Meteoroid Impacts…

• Moon has many craters (largest the size of Indiana), while Earth only has about a dozen recognizable impact craters.

Why do we see more traces of Asteroid impacts on the moon, than we do on Earth?

• Moon has no atmosphere, therefore: – No weathering or erosion– No tectonic forces (volcanic

eruptions and plate movements)

When/How was the moon formed?

One hypothesis…When solar system first

formed…

1. Body the size of Mars impacted Earth

2. Liquefied Earth’s surface ejecting huge quantities of crustal and mantle rock

3. Some debris entered orbit and later combined to form the moon

Lunar Features

• Highlands – Cover far-side of the moon

• Highest peak almost has tall as Mt. Everest

• Maria – dark, smooth area.

• Ancient beds of lava• Regolith – layer of

gray debris from meteorite bombardment (igneous rocks, glass beads, fine lunar dust)

Relationships between Sun, Moon, & Earth:

• Sun provides light, warmth, and energy• Moon raises tides and illuminates night

sky• Every society in our history has based

their calendar and time keeping system on motions of the Sun and Moon

Annual Motions

Which Picture Represents ourSpring, Summer, Fall, and Winter?

Relationship between theEarth, Moon, and Sun

Why are the Dinosaurs Extinct?

One hypothesis…• Mass extinction 65

million years ago• Due to inability to adapt

to some radical change in environmental conditions

• Huge meteorite (10 km diameter) collided with Earth around Yucatan Peninsula

• What would have been effects of huge collision?

• Huge amounts of Dust and other debris blasted high into the atmosphere

• Blocked out sunlight which stopped photosynthesis

• Food chains collapsed

• By the time sunlight returned, more than ½ of species on Earth had been whipped out

• How do we know that?

Early Earth:Very Different than it is today!

• Original atmosphere made up of gases similar to those released in volcanic eruptions today (Water vapor, CO2, Nitrogen, and several trace gases)

• There was no OXYGEN!!• Oxygen began to accumulate in the

atmosphere about 2.5 billion years ago.• Believed to be similar to atmospheres

of Venus

Evidence of things from the past…

• Rocks record geological events and changing life forms of the past

• Earth’s surface and interior have been changed by the same geological processes that continue today (uniformitarianism)

• Relative and Radiometric Dating helps to give scientists an idea of how old things are.

Relative Dating

• Tells us the sequence in which events occurred

• Each bed of rock is older than the one above it and younger than the one below it.

• allows us to compare rock layers in different geographic areas.

Correlation of Rock Layers

Radiometric Dating

Fossil Formation

Two Conditions are important for preservation:1. Rapid Burial2. Possession of Hard Parts

Fossils and Correlation• Any time period can

be recognized by its fossil content

Index Fossils:• Widespread

geographically• Short Life Span of

geological Time• Occur in Large

Numbers• Important to

geologists to match rocks of the same age.

Fossils can also be usedto interpret and describe ancient environments.

Geologic Time Scale• Using their

interpretations of the rock record, geologists have divided Earth’s 4.56 billion year history into units that represent specific amounts of time

• It was believed early Earth had one large land mass (Pangaea) which separated into today’s continents through plate movements.