Chapter: The Solar System

Chapter: The Solar System

Table of Contents

Section 2: The Inner Planets

Section 1: Planet Motion

Section 3: The Outer Planets

Section 4: Life in the Solar System

Models of the Solar System

• In the geocentric model of the solar system, Earth is considered the center and everything else revolves around it.

Planet Motion

1

Geocentric Model

Heliocentric Model• Earth-centered model held until 1543.

Planet Motion

1

• Nicholas Copernicus published a different view.

• Copernicus stated that the Moon revolves around Earth.

• Earth and the other planets revolve around the Sun.

Heliocentric ModelPlanet Motion

1

• The apparent motion of the planets, the stars, and the Sun is due to Earth’s rotation. This is the heliocentric model, or Sun-centered model of the solar system.

Heliocentric Model• Galileo Galilei found evidence that

supported the ideas of Copernicus.

Planet Motion

1

• He observed that Venus went through phases like the Moon’s.

• He also saw moons in orbit around Jupiter.

Understanding the Solar System• In the early 1600’s, Kepler discovered that

the planets travel around the Sun in ellipses, not circles.

Planet Motion

1

• Planets travel at different speeds in their orbits.

• The astronomical unit (AU) equals the average distance from Earth to the Sun, about 150 million km.

Classifying Planets• One system uses sizes and other

characteristics.

Planet Motion

1

• Those similar to Earth are called terrestrial planets, giant planets are jovian planets.

• Two other systems classify planets by location.

Classifying Planets• Planets whose orbits are between the Sun

and the asteroid belt as inner planets and those beyond the asteroid belt as outer planets.

Planet Motion

1

• The other system classifies planets whose orbits are between Earth’s orbit and the Sun as inferior planets, and those whose orbits are beyond Earth’s orbit as superior planets.

Other Solar Systems• Extrasolar planets—planets in orbit

around other stars—are helping astronomers learn how planetary systems form.

Planet Motion

1

• Astronomers have devised new techniques and instruments to find planets around other stars.

Section Check

1Question 1

Who was responsible for developing the geocentric model of the solar system?

A. AristotleB. CopernicusC. GalileoD. Ptolemy

Section Check

1 AnswerThe answer is D. Ptolemy presented his geocentric model of the solar system in 140 A.D.

Section Check

1Question 2

Approximately how long is an astronomical unit?

A. 100 kmB. 100 million kmC. 150 million kmD. 200 billion km

1Section Check

AnswerThe answer is C. One astronomical unit equals the average distance from Earth to the Sun, about 150 million km.

Section Check

1Question 3

_______ are planets in orbit around stars other than our Sun.

A. Extrasolar planetsB. Extrasensory planetsC. Intersolar planetsD. Intrasolar planets

1Section Check

Answer

The answer is A. Scientists have discovered extrasolar planets around Upsilon Andromedae.

The Inner Planets

2 Planets near the Sun

• Mercury is covered by craters.

• The second-smallest and closest planet to the Sun is Mercury.

• Mercury has a much larger iron core than would be expected and is missing some lighter materials.

The Inner Planets

2 Planets near the Sun

• As the outer layers adjusted, they wrinkled, forming dramatic cliffs as high as 3 km.

• Mercury’s large, solid core shrank much more rapidly than its thin outer layers.

• Mercury has no true atmosphere.

• Surface temperatures vary from 427ºC to -170ºC.

The Inner Planets

2 Venus

• Venus is blanketed by a dense atmosphere.

• Venus is the second planet from the Sun.

• Due to this intense greenhouse effect, temperatures on the surface of Venus are between 450ºC and 475ºC.

The Inner Planets

2 Venus • Heat radiated from Venus’s surface is

absorbed by the carbon dioxide gas, causing what is called a greenhouse effect.

• Temperatures on Earth allow water to exist as a solid, a liquid, and a gas.

The Inner Planets

2 Earth • The third planet from

the Sun is Earth.

• Ozone in Earth’s atmosphere protects life from the Sun’s intense radiation.

• Other Martian features are the polar ice caps and changes in the coloring of Mars’s surface.

The Inner Planets

2 Mars • The fourth planet from the Sun, Mars,

is called the red planet because of iron oxide in some of the weathered rocks.

The Inner Planets

2 Mars • The polar ice caps

are made of frozen carbon dioxide and frozen water.

The Inner Planets

2 Mars • The Martian atmosphere is much thinner

than Earth’s and is composed mostly of carbon dioxide with some nitrogen and argon.

• Mars has two small, heavily cratered moons called Phobos and Deimos.

The Inner Planets

2 NASA on Mars • The Mariner 9 space probe orbited

Mars in 1971-1972.

• Valles Marineris is a large canyon that was discovered by this early mission.

• Mariner 9 also found large, extinct volcanoes.

The Inner Planets

2 The Viking Probes • In 1976, the Viking 1 and Viking 2

probes landed on Mars.

• The Viking 1 and Viking 2 orbiters photographed the entire surface of Mars from orbit.

• Landers conducted meteorological, chemical, and biological experiments on the planet’s surface.

The Inner Planets

2 Global Surveyor, Pathfinder, and Odyssey

• Global Surveyor showed that the walls of Valles Marineris have distinct layers similar to those of the Grand Canyon.

• Mars Odyssey, provided evidence for water as frost beneath a thin layer of soil in the far northern and southern parts of Mars.

The Inner Planets

2 Global Surveyor, Pathfinder, and Odyssey

• The Mars Pathfinder and its rover, Sojourner, gathered data that indicated that iron in Mar’s crust may have been leached out by groundwater.

2Question 1

Which planet is closest to the Sun?

A. MarsB. MercuryC. Earth D. Venus

Section Check

2Answer

The answer is B. Mercury is the closest planet to the Sun. Venus is the second planet from the Sun.

Section Check

2Question 2

Which planet has size and mass similar to Earth’s?

A. JupiterB. MercuryC. PlutoD. Venus

Section Check

2Answer

The answer is D. Venus has similar size and mass but the temperatures on its surface are between 450º C and 475º C.

Section Check

2Question 3

Earth is the __________ planet from the Sun.

A. secondB. thirdC. fourthD. fifth

Section Check

2Answer

The answer is B. Mercury and Venus are closer to the Sun than Earth.

Section Check

Jupiter• The largest and fifth

planet from the Sun is Jupiter.

The Outer Planets

3

• It is composed mostly of hydrogen and helium.

Jupiter

The Outer Planets

3

• Continuous storms of swirling, high-pressure gas have been observed on Jupiter.

• The Great Red Spot is the most spectacular of these storms.

• In 1979, Voyager1 and Voyager 2 flew past Jupiter, and the Galileo space probe reached Jupiter in 1995.

Space Probes to Jupiter

The Outer Planets

3

• The major discoveries of these probes include information about the composition and motion of Jupiter’s atmosphere, characteristics of some of its moons and the discovery of new moons.

• Four are large enough to be considered small planets.

Jupiter’s Moons

The Outer Planets

3

• These Galilean moons of Jupiter are Io, Europa, Ganymede, and Callisto.

Jupiter’s Moons

The Outer Planets

3

• Ganymede is larger than the planet Mercury and is the largest moon in the solar system.

• Io is under a constant tug-of-war between the gravities of Jupiter and Europa.

• This heats up the interior of Io and causes it to be the most volcanically active body in the solar system.

Saturn

The Outer Planets

3

• Saturn is the sixth planet from the Sun and is known as the ringed planet.

• Saturn is a large planet with a thick outer atmosphere composed mostly of hydrogen and helium with some ammonia, methane, and water vapor.

Saturn’s Rings

The Outer Planets

3

• Saturn’s rings are composed of countless ice and rock particles ranging in size from a speck of dust to tens of meters across.

• Pictures of these rings showed a density wave and areas where the ring material bends up and down.

Uranus

The Outer Planets

3

• Uranus, is the seventh planet from the Sun.

• It is a large planet with 27 moons.

• The atmosphere of Uranus contains hydrogen, helium, and about two percent methane.

• The methane gives the planet its blue-green color.

Neptune

The Outer Planets

3

• Neptune, another large planet similar in size to Uranus, is the eighth planet from the Sun.

• Neptune’s atmosphere is similar to that of Uranus, but has a little more methane—about 3 percent—causing it to look bluer.

Pluto

The Outer Planets

3

• Pluto, is farther from the Sun than Neptune during most of its orbit, it is considered the ninth planet from the Sun.

• As a comet approaches the Sun, it begins to vaporize. The released dust and gases form a bright cloud called a coma around the nucleus. The solar wind pushes on the vaporized coma, forming a tail that always points away from the Sun.

Comets and Other Objects

The Outer Planets

3

• A comet, is composed of dust rock particles mixed with frozen water, methane, and ammonia.

• Once in orbit around the Sun, comets reappear at predictable times.

Comets and Other Objects

The Outer Planets

3

• Most comets come from two places—a vast disk of icy comets called the Kuiper Belt near Neptune’s orbit and the Oort cloud.

• Most asteroids are found in a belt between the orbits of Mars and Jupiter.

Comets and Other Objects

The Outer Planets

3

• Rocky objects formed from material similar to that of the planets are called asteroids.

• Asteroids range in size from tiny particles to objects 940 km in diameter.

• Meteoroids may enter the atmosphere.

Comets and Other Objects

The Outer Planets

3

• Other rocky objects orbiting within the solar system are meteoroids.

• Most burn up completely and we see them as meteors or “shooting stars.”

• Others do not burn completely and strike Earth.

• These are called meteorites.

• Sedna has been labeled a distant planetoid and with a diameter of 1,200 to 1,700 km, it is smaller than Pluto, but larger than comets in the Kuiper Belt.

Comets and Other Objects

The Outer Planets

3

Section Check

Question 1

The fifth planet from the Sun is __________.

A. JupiterB. NeptuneC. SaturnD. Pluto

3

Section Check

Answer

The answer is A. Jupiter is the largest planet in the solar system.

3

Section Check

Question 2

Which of Jupiter’s large moons is closest to Jupiter and the most volcanically active object in the solar system?

A. CallistoB. EuropaC. GanymedeD. Io

3

Section Check

Answer

The answer is D. Jupiter exerts tremendous gravitational pull on Io.

3

Section Check

Question 3

It takes Pluto __________ to orbit the Sun one time.

3

A. 2 yearsB. 24 yearsC. 124 yearsD. 248 years

Section Check

Answer

The answer is D. During part of its orbit, Pluto is closer to the Sun than Neptune, but is still considered to be the ninth planet from the Sun.

3

Life as We Know It

• A research submarine, the Alvin, found some interesting life-forms while exploring hot, volcanic vents on the ocean floor.

• Life-forms found included crabs, clams, and tubeworms.

Life in the Solar System

4

Exotic Life on Earth

• Alvin also discovered colonies of bacteria living off the extremely hot material spewing from volcanic vents.

Can life exist on other worlds?• Extraterrestrial life is life on other

worlds.

• Let’s take a look at some places where scientists are searching for extraterrestrial life.

Life in the Solar System

4

Mars• Evidence from space probes has shown

that Mars probably had large amounts of water on its surface.

• If life existed and left evidence, future astronauts will find it.

Life in the Solar System

4

Europa• Europa’s ocean could hold more than

twice the amount of water that Earth’s oceans hold.

• If life can exist in extremely hot liquid flowing from volcanic vents on Earth’s ocean floor, could it not exist in a similar environment if it exists on Europa?

Life in the Solar System

4

Titan• Saturn’s moon, Titan is larger than

Mercury and has an atmosphere composed mostly of nitrogen.

• The presence of hydrocarbons on the surface of Titan interests exobiologists, scientists who search for evidence of life on other worlds.

Life in the Solar System

4

Titan

Life in the Solar System

4

• The apparent absence of large impact craters indicates that Titan has experienced internal geologic activity.

• This activity could provide the energy needed for organic molecules to develop into the building blocks of life.

Section Check

Question 1

What is extraterrestrial life?

4

Answer

Extraterrestrial life is life that exists on other planets.

Section Check

Question 2What makes scientists think that Europa’s ocean could contain life?

4

AnswerScientists think that the ocean might be deep and long-lasting, possibly even liquid water that is warmed by Jupiter’s gravitational pull on Europa.

Section Check

Question 3

Which performed tests for life on Mars?

A. AlvinB. Huygens probeC. Galileo probeD. Viking probe

4

Section Check

Answer

The answer is D. The Viking experiments found no evidence of life on Mars.

4

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