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Chapter Introduction

Lesson 1 Our Solar System

Lesson 2 Life in the Solar System

Lesson 3 Human Space Travel

Chapter Wrap-Up

NASA

How and where do scientists look for life in the solar system?

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What do you think?

Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.


1. Our solar system has eight planets.

2. Earth’s atmosphere is mostly oxygen.

3. Earth’s atmosphere protects life on Earth from dangerous solar radiation.

4. Scientists think conditions for life might exist on some moons in the solar system.

Do you agree or disagree?


5. Astronauts float in space because there is no gravity above Earth’s atmosphere.

6. The United States is the only country with a human space-flight program.



• How do objects in the solar system move?

• How did distance from the Sun affect the makeup of objects in the solar system?

• What objects are in the solar system?

Our Solar System


• astronomical unit

• planet

• dwarf planet

• satellite

Our Solar System

• meteoroid

• meteor

• meteorite


• Five billion years ago, our solar system formed from a spinning cloud of hydrogen gas and dust.

• When gravity caused the cloud to collapse, the cloud began to spin faster and grow hotter.

Origin and Structure of Our Solar System


• When the center of the cloud became hot enough for nuclear reactions to occur, a star formed—the Sun.

• Small pieces of ice and rock orbiting the Sun clumped together and formed planets, asteroids, and other objects.

Origin and Structure of Our Solar System (cont.)


Scientists use astronomical units to measure distances in our solar system. An astronomical unit (AU) is Earth’s average distance from the Sun, nearly 150 million km.


• The inner solar system—containing Mercury, Venus, Earth, and Mars—extends to about 4 AU from the Sun.

• It also contains the asteroid belt between Mars and Jupiter, 2–4 AU from the Sun.



• The outer solar system contains the planets Jupiter, Saturn, Uranus, and Neptune.

• The solar system is often divided into regions depending on distance from the Sun.



The outer solar system extends from Jupiter’s orbit to the Oort cloud—a large, spherical shell of icy planetesimals that scientists think orbits the Sun from about 5,000 AU to as far as 50,000 AU away.



• The solar system is made mostly of hydrogen gas.

• Ices, rocks, and metals make up less than 2 percent of our solar system’s mass.



• The Sun’s gravity pulls on planets and other objects that revolve around it.

• The Sun and six of the eight planets, including Earth, rotate in a counterclockwise direction.


• Venus and Uranus rotate clockwise.

• While Earth rotates from west to east, objects in the sky appear to move from east to west.

Movement in the Solar System (cont.)


Movement in the Solar System (cont.)

Why do most objects in our solar system move in the same direction?


• Scientists group objects in our solar system into categories based on makeup, size, distance from the Sun, and whether the object orbits the Sun or another object.

• As regions beyond the Sun cooled, some of the gases solidified into ices, rocks, and metals.

Objects in Our Solar System


Objects in Our Solar System (cont.)

How did the distance from the Sun affect the makeup of objects in the solar system?


• The Sun is made mostly of hydrogen gas.

• The Sun is the only star in our solar system, and it the largest object in the solar system.

• The Sun’s diameter is 10 times that of Jupiter and more than 100 times that of Earth.



A planet orbits the Sun, is large enough to be nearly spherical in shape, and has no other large objects in its orbital path.



The four inner planets formed from rocks and metal, are smaller than the outer planets, have few or no moons, and rotate slowly.



The four outer planets formed mostly from gas and ice, are large, have many moons, rotate quickly, and have rings.



• Dwarf planets orbit the Sun and are nearly spherical in shape, but they share their orbital paths with other objects of similar size.

• There are at least five dwarf planets in our solar system, but scientists think the solar system might contain hundreds—most of them orbiting the Sun beyond Neptune.




• All known dwarf planets, including Pluto, are smaller than Earth’s moon.

• Ceres orbits the Sun between the orbits of Mars and Jupiter, in the asteroid belt.


Asteroids are small, rocky or metallic objects that are remnants from the solar system’s formation.


NASA/JPL/USGS


• A satellite is an object that orbits a larger object other than a star.

• Natural satellites are also known as moons.

• There are over 170 moons in the solar system.



• Like the asteroid belt, the Kuiper belt contains remnants from the solar system’s formation.

• Kuiper belt objects are mostly ice.



Comets are small objects made mostly of ice which revolve around the Sun with long, stretched-out orbits.


NASA


Kuiper belt objects orbit the Sun beyond Neptune. Some comets originate in the Kuiper belt. Others originate farther away.

NASA


• A meteoroid is a solar system object that is smaller than an asteroid or a comet.

• A meteor is the streak of light created when a meteoroid enters Earth’s atmosphere.

• A meteorite is a meteoroid that strikes Earth.




meteor

from Greek meteoros, means “high up”



What objects are in our solar system?


• The inner solar system extends from the Sun through the asteroid belt.


• Even some asteroids have satellites.

NASA/JPL/USGS


• Comet tails can be millions of kilometers long.


What orbits the Sun, is large enough to be nearly spherical, and has no other large objects in its orbital path?

A. dwarf planet

B. meteoroid

C. planet

D. satellite


A. gas

B. ice

C. metal

D. rock

The majority of objects in the Kuiper belt are comprised of which type of matter?


A. asteroid

B. comet

C. meteoroid

D. dwarf planet

How is Pluto classified?


1. Our solar system has eight planets.

2. Earth’s atmosphere is mostly oxygen.



• What conditions on Earth enable life to exist?

• What conditions on other bodies in the solar system might enable life to exist?

• Where might life possibly exist beyond Earth?

Life in the Solar System


• astrobiology

• organic

• geyser

Life in the Solar System


• Despite the extreme conditions in which some organisms live, all of Earth’s life-forms need the same basic things to survive: a source of energy, liquid water, and nourishment.

• Astrobiology is the study of the origin, development, distribution, and future of life in the universe.

Conditions for Life on Earth


Conditions for Life on Earth (cont.)

astrobiology

from Greek astron, means “star”; Greek bios, means “life”; and Greek logia, means “study of”



What do organisms on Earth need to survive?


• The Sun is the source of almost all energy on Earth.

• Sunlight provides light and thermal energy.

• A small percentage of organisms on Earth receive energy from chemicals or from Earth itself.



• Earth’s atmosphere absorbs sunlight during the day and keeps thermal energy from escaping into space at night.

• Earth’s atmosphere absorbs most of the Sun’s ultraviolet light, as well as X-rays and other potentially harmful light from the Sun.

• Earth’s atmosphere also protects Earth’s surface from meteoroids.



• Liquid water is necessary for all life on Earth.

• Depending on temperature and pressure on Earth, water is solid, liquid, or gas.


Royalty-Free/CORBIS


Water changes from a liquid to a gas or to a solid as its temperature and pressure change.



What would happen to water on Earth’s surface if Earth had no atmosphere?


• Living things are nourished by nutrients they take from the air, water, and land around them.

• All molecules that provide nourishment for life on Earth contain carbon.

• Organic refers to a class of chemical compounds in living organisms that are based on carbon.




organic

Science Use relating to carbon compounds in living organisms

Common Use relating to food grown without fertilizers, pesticides, or antibiotics


Though it is possible that inorganic life could exist elsewhere, astrobiologists are most interested in places beyond Earth where water is liquid and carbon is plentiful.



• Because liquid water is essential for life on Earth, scientists look for places in our solar system, on the Moon, and beyond where liquid water might exist or might have existed in the past.

• Other than Earth, Mars is the planet scientists think is most likely to have liquid water.

Looking for Life Elsewhere


There is abundant evidence for water vapor and water ice on the Martian surface, and photographs show surface features on Mars that appear to have been carved by moving water.

Looking for Life Elsewhere (cont.)



Why do scientists think liquid water once might have existed on Mars?


Several moons in the outer solar system, such as Jupiter’s moon Europa, have surface features that indicate the presence of liquid water not far below.


NASA/JPL/University of Arizona/University of Colorado

Galileo Project/JPL/NASA


• Several other moons in the outer solar system, including Enceladus, a moon of Saturn, and Triton, a moon of Neptune, show evidence of geysers.

• A geyser is a warm spring that sometimes ejects a jet of liquid water or water vapor into the air.




Where might life exist in the solar system beyond Earth?


• Most—but not all—life on Earth receives energy from the Sun.

• Features on Mars that look like streambeds might be evidence that liquid water once existed on the surface.

• Oceans of liquid water might be below the surface of some moons in the outer solar system.

Galileo Project/JPL/NASA


In addition to a source of energy and nourishment, what do all of Earth’s life-forms need to survive?

A. ice

B. oxygen

C. liquid water

D. water vapor


Which term describes a class of chemical compounds in living organisms that are based on carbon?

A. astrobiology

B. geyser

C. meteoroid

D. organic


A. Jupiter

B. Mars

C. Saturn

D. Venus

Other than Earth, what planet do scientists think is most likely to have liquid water?


3. Earth’s atmosphere protects life on Earth from dangerous solar radiation.

4. Scientists think conditions for life might exist on some moons in the solar system.



• What technology has allowed humans to explore and travel into space?

• What factors must humans consider when traveling into space?

Human Space Travel


• artificial satellite

• rocket

• space probe

Human Space Travel


• An artificial satellite is any human-made object placed in orbit around a body in space.

• Hundreds of artificial satellites, such as communication satellites, operate in orbit around Earth.

Technology and Early Space Travel

U.S. Department of Defense


• A rocket is a vehicle propelled by the exhaust made from burning fuel.

• Rockets allow artificial satellites to escape Earth’s gravity.

Technology and Early Space Travel (cont.)


• A space probe is an uncrewed vehicle that travels to and obtains information about objects in space.

• Probes are equipped with cameras and scientific instruments that transmit data back to Earth.

Robotic Space Probes

Digital Vision/Getty Images


• It costs less and is safer to send probes rather than people into space.

• Another reason to send probes rather than people into space is that objects in space are very far away.

Robotic Space Probes (cont.)


• The National Aeronautics and Space Administration (NASA) is the U.S. government agency responsible for most space missions and space-flight technology.

• Astronauts from more than 30 countries have traveled to space, and several countries have sent robotic missions to the Moon and beyond.




astronaut

from Greek astron, means “star”; and Greek nautes, means “sailor”



How do space probes help scientists explore space?


• When astronauts travel into space, they must bring their environments and life-support systems with them.

• Astronauts must rely on their spacecraft and spacesuits to shield them from dangerous solar radiation and solar particles.

Challenges for Humans in Space

NASA


• Air circulation systems inside spacecraft supply oxygen and keep carbon dioxide, which people breathe out, from accumulating.

• Environmental control systems in spacecraft protect astronauts from temperature and pressure extremes.

Challenges for Humans in Space (cont.)


• Astronauts in orbit around Earth are subjected to almost the same gravity as they are on Earth’s surface.

• As their spacecraft orbits Earth, the astronauts inside are continually falling toward Earth, but because their spacecraft is moving, they float instead of fall.




What factors must humans consider when traveling into space?


• The space environment that astronauts experience is called microgravity.

• Microgravity exerts a smaller force on the astronauts’ bodies than the force of gravity they would experience on Earth.



• Living in microgravity, astronauts do not have to work as hard as they would on Earth to move around.

• Astronauts in space must exercise each day to keep their bodies strong for their return to Earth.



The International Space Station (ISS) is a large, artificial satellite that orbits Earth.

Living and Working in Space


• The ISS crew conducts scientific and medical experiments.

• In the future, in addition to being an orbiting research laboratory, the ISS might serve as a testing and repair station for missions to the Moon and beyond.

Living and Working in Space (cont.)


• Space transportation systems are the rockets, the shuttles, and other spacecraft that deliver cargo and humans to space.

• The space shuttle was NASA’s first reusable transportation system.

Living and Working in Space (cont.)

Stocktrek/age fotostock


NASA is designing a new space transportation vehicle called Orion, with a goal of sending astronauts to the Moon and eventually to Mars.


• When wearing an EMU suit, an astronaut can spend up to eight hours outside a spacecraft.

• Sleeping can be a challenge for astronauts in space.

• The space shuttle was NASA’s first reusable transportation system.

Stocktrek/age fotostock


Which U.S. government agency is responsible for most space missions and technology?

A. EMU

B. ISS

C. NASA

D. Orion


A. rocket

B. satellite

C. space probe

D. space shuttle

Which is an uncrewed vehicle that travels to and obtains information about objects in space?


A. carbon dioxide

B. gravity

C. nitrogen

D. oxygen

Air circulation systems inside spacecraft supply oxygen and keep what from accumulating?


5. Astronauts float in space because there is no gravity above Earth’s atmosphere.

6. The United States is the only country with a human space-flight program.



Key Concept Summary

Interactive Concept Map

Chapter Review

Standardized Test Practice

Scientists use space probes, artificial satellites, and human transportation systems to explore our solar system and look for evidence of life on Mars and some moons.

• Our solar system formed from a spinning cloud of gas and dust. Most of the planets and other solar system objects orbit the Sun in the same direction the original cloud rotated.

• The Sun is made mostly of hydrogen gas. Objects close to the Sun are made mostly of rock and metals. Objects farther away are made mostly of ices and gases.

• The solar system includes the Sun, planets, dwarf planets, comets, natural satellites, asteroids, and meteoroids.

Lesson 1: Our Solar System

Lesson 2: Life in the Solar System

• Life on Earth requires a source of energy, liquid water, and nourishment.

• Scientists search for places in the solar system where liquid water and organic carbon might exist.

• Scientists think life could possibly exist on Mars and/or some satellites of the outer planets.

• Humans have developed rockets, space probes, artificial satellites, and human transportation systems to help them explore and travel into space.

• When traveling, working, and living in space, humans must be protected from radiation, temperature and pressure extremes, and meteoroids. They must provide their own oxygen, and they must be prepared for a microgravity environment.

Lesson 3: Human Space Travel

A. satellites

B. meteoroids

C. dwarf planets

D. comets

Which refers to objects that orbit the Sun and are nearly spherical in shape but share their orbital paths with other objects?


A. comet

B. meteor

C. meteorite

D. satellite

Which terms describes the streak of light created when a meteoroid enters Earth’s atmosphere?


A. carbon

B. life in the universe

C. stars

D. water

Astrobiology is the study of the origin, development, distribution, and future of which of these?


A. carbon

B. oxygen

C. the Sun

D. water

What is the source of almost all energy on Earth?


A. artificial satellite

B. rocket

C. space probe

D. space shuttle

Which describes any human-made object placed in orbit around a body in space?


A. hydrogen

B. ice

C. metals

D. rocks

What makes up most of the solar system?


A. comet

B. dwarf planet

C. planet

D. satellite

Which term refers to an object that orbits a larger object other than a star?


A. carbon

B. liquid water

C. solid water

D. sunlight

What is necessary for all life on Earth?


A. artificial satellite

B. rocket

C. satellite

D. space probe

Which vehicle is propelled by the exhaust made from burning fuel?


A. International Space Station

B. Orion

C. space probe

D. space shuttle

Which describes NASA’s first reusable transportation system?


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