Focus on California 8th Grade Physical Science Textbook Chapter 14 The Solar System

Chapter 14 The Solar System ' A ( Standards Unbalanced forces cause changes in . As a basis for understanding this Student know the mic of gravity and the shapes or , stars , and the system . The structure and tion of the universe can be learned from studying stars and galaxies and their evolution . As a basis for understanding this Students know that the Sim us one many stars the Milky Way and that stars may size , and to or Students knew how to use units and years as of between the Sun , stars , and Earth . Students know that stars are the source of tight for all in outer space and that the Moon and plan ets by reflected sunlight . not by her own . Students know the , genera , position and size , and motion of objects in the System , planets , comets and ! Illustration shows several planets ) orbit the sun

a Preview What types of objects are found in the solar system ?

Check What You Know Suppose you were twirling a ball attached to a string over your head . If the string were to suddenly break , what do you think would happen to the ball ?

Explain your answer . 14 533 the images shown hen represent some of the key in this . You can use this vocabulary skill to help you understand the meaning of some key in this chapter . Greek Word Origins Many science words related to astronomy ( ome from ancient Greek . In this chapter you will learn the word , which comes from the Greek words geo , meaning and , meaning . Early Greeks believed in a universe , one in which was at the center . gee Earth center Learn these Greek words to help remember key terms . I Meaning Key Terms i Apply It ! have learned about .

Chapter 14 Vocabulary Section , re ( I ( moan Section ( core corona solar sunspot Em ?

solar flare Section Section , gas giant Section ( hell bell ( cloud Section MI Build ( Vocabulary , PHir Chapter 14 535 I Create Outlines You have learned to identify main ideas and supporting details as you read this textbook . An outline shows the relationship between main ideas and supporting details . An outline has a formal structure as in the example shown Roman numerals show the main topics . Capital letters Show . Numbers show supporting details , including key terms . Preview and then look at the outline below . Observing the Solar Earth at the Center Observations . at the center of planets and stars Kev Model . Plants an small that move an . Medal was incorrect , but accepted details far years . at the Center A . Apply It ! Answer ( of the following questions in a complete sentence . What are the most important topics in this outline ?

Where in this outline can you lind the of the key ?

Build a Model of the Solar System The solar system is a vast region ( the sun , planets , and many other objects . To help you understand the huge distances , you design three different scale models of the solar system . Your Goal To design scale models of the solar system To complete investigation . you will ' a model to show the planets distances from the sun a model to show the planets compared to the sun test different scales to see uf you can use the same scale for both size and distance in one model Plan It ! by previewing Figures 13 and this and Appendix on pages 654 and 655 . a group of classmates . brainstorm how to build your models . Then design two to show distances and one to show diameters . Next , design a third model that uses the same scale for both size and . Try several different scales to whith works best . Prepare a data table to rE ( your calculations . You present your scale models and graphs at the end of the chapter . Chapter 14 .

( All Standards Fo Students know how to use astronomical units and light years as of distance between the Sun . stars . and Earth . and Students know that stars are the source tor all bright omens in outer and that the Moon and planets shine by ed sunlight , not by their own light what are the and ( systems ?

How did Copernicus . Galileo . and contribute to our knowledge 01 the solar system What make up the solar system ?

Key Terms I geocentric I helio ( I ellipse I moon I astronomical Observing the Solar System use What Is at the Center ?

I . Stand about meters from a partner who is holding a flashlight . Have your partner shine the in your direction . Tell your partner not to move the flashlight . Continue facing your partner , but move sideways in a circle , staying about meters away from your partner . Record your observations about your ability to see the light . Repeat the activity , but this time remain stationary and continually face one direction . Have your partner continue to hold the flashlight toward you and move sideways around you , remaining about meters from you . Record your observations about your ability to see the , Think It Over Drawing Conclusions Compare your two sets of observations . If you represent Earth and your partner represents the sun , is it possible , just from your observations , to tell whether Earth or the sun is in the center of the solar system ?

you ever up the sky on it starry night ?

If you mulch for several hours . the star seem to move , the sky . The sky ( to be rotating right over your head . In fact , from the Northern ' the slut appears to tIl ' around the North Star every 24 hours . Now think about what you . i dill During the day . the tun appears to move across the From ( Ill , it as if Earth is stationary that the sun . lIl ( and stars are moving Earth . But is the really you ?

ago . before their were space shuttles or . was mi catty to . I Star Trails photo was made by exposing the camera film for several hours . Each star trails along a circle , and all the stars seem to revolve around the North Star .

Earth at the Center When the ancient Greeks watched the stars move across the sky . they noticed that the patterns of the stars did change . Although the stars seemed to move . they stayed in the same position relative to one another . These patterns of stars . called constellations . kept the same shapes from night to night and from year to year . Greek Observations As the Greeks observed the sky . they noticed something surprising . Several points oflight seemed to wander slowly among the stars . The Greeks called these objects planets . from the Greek word meaning Wanderers . The Greeks made careful observations of the motions of the planets that they could see . You know these planets by the names the ancient Romans later gave them Mercury . Venus . Mars . and Saturn . Most early Greek astronomers believed the universe to be . with Earth at the center . The Greeks thought that Earth is inside a rotating dome they called the celestial sphere . Since get ) is Greek for Earth . an model is known as a ( oh SEN ) system . In I system , Earth is at the center of the revolving planets and stars . Ptolemy Modal About . the Greek astronomer Ptolemy ( uli mec ) further developed the geocentric model . Like the earlier Greeks . Ptolemy thought that Earth is at the center of a system of planets and stars . In Ptolemy model , however , the planets move on small circles that move on bigger circles . Even though Ptolemy geocentric model was incorrect , it explained the motions observed in the sky fairly accurately . As a result . the geocentric model of the universe was widely accepted for nearly years after Ptolemy . i What Is a system ?

Flour System In a geocentric system , the planets and stars are thought to revolve around a stationary Earth . In the an astronomy book published the illustration oi geocentric system shown below . Diagrams Where is Earth located in each illustration 14 539

Sun at the Center Not everybody believed in the geocentric system . An ancient Greek scientist developed another explanation for the motion ofthe planets . This model is called a heliocentric ( hee lee oh SEN ) Ina heliocentric system . Earth and the other planets revolve around the sun . This model was not well received in ancient times , however . because people could not accept that Earth is not at the center of the universe , lhe Copernican Revolution In 1543 , the Polish mer Copernicus further developed the heliocentric model . Copernicus worked out the arrangement of the known planets and how they move around the sun . cus theory would eventually the science of astronomy . But at first , many people were unwilling to accept his theory . the 15005 and early , most people still believed in the model . However , evidence collected by the ltalian scientist Galileo eventually proved that the heliocentric model was correct . Galileo Evidence used the newly invented telescope to make discoveries that supported the heliocentric ! model . For example . in . Galileo used a telescope to planets revolve around A we hy ' four moons revolving around . is proved aw ) was that not every body in space revolves around Earth . in 1550 , Galileo observations of Venus also supported the ! centric system . Galileo knew that Venus is always seen near the heliocentric model . what revolves Wound Em sun . He discovered that Venus goes through a series of phases similar to those of moon . But Venus would not have a full set of phases if it circled around Earth . Therefore , Galileo reasoned . the geocentric model must be incorrect . A reconstruction of Galileo telescope ! Galileo 642 I Major Figures in the History of Astronomy 5400

Motions of the Planets ( correctly placed the sun at the center the planets . But he incorrectly that the planets travel in orbits that are perfect circles . Copernicus had based his on tions made by the ancient Greeks . Observations In the late . the Danish astronomer Tycho ( BRAH uh ) and his much more accurate observations . For more than 20 years . they carefully observed and recorded the positions of the planets . Surprisingly . these observations were made out using a telescope . Telescopes had not yet been First Law Tycho died in . assistant . went to work analyzing the observations . used Tycho data to develop three laws that describe the motions of the planets . began by trying to figure out the shape of orbit . At first . he assumed that the orbit was a perfect circle . But his calculations did not fit the observations . eventually found out that Mars orbit was a slightly circle . or ellipse . An ellipse is an oval shape , which maybe elongated or nearly circular . After years of detailed calculations . reached a able conclusion about the motion of the planets . found that the orbit of each planet is an ellipse . This is now known as lirst law of motion . had used the ered by Tycho to disprove the belief that the planets move in perfect circles . What is the heliocentric system ?

Tycho 601 observatory on an island between Denmark and Sweden 79 , Activity A Loopy Ellipse Vou can draw an ellipse . Carefully stick two pushpins about 10 apart through a sheet of white paper on top of corrugated cardboard . One pushpin represents the sun . Tie the ends of a piece of string together . Place the string around the pushpins . Keeping the string tight . move a pencil around inside the string . Now place the pushpins apart . Repeat Step . Predicting How does changing the distance between the pushpins affect the ellipse shape ?

What shape would you draw it you used only one Is the sun at the center of the ellipse ?

Johannes 0541 Chaotic 14 ! 39 AU , AU Earth , AU Mart 228 . 00 . AU Jupiter Saturn , AU AU mu Second Law ( huw the The Sun and Planets ul giver planet changes it Mound the sun . lound that with I ' it is ( to sun ' I I . he ' and lower when It farther the sun . sun The solar system also ( smaller ( SU ( as Pluto , 15 drawn to scale , but planets are not Third Law also that the tune that lakes to orbit the sun and it . planer dose sun are related . He found that closer to the the sun than that sun Yuu can use third law of motion to ' sun long it lot the planet to one . Math and . Speed of Planets Data Planet Speed Versus Distance Use the graph to help what learned about the between the speed of a planet and lrom the sun . Reading Graphs According to the graph , what is Earth average speed ?

Data is closer to the sun , Mercury or Mars ?

moves faster ?

Speed ( Conclusions What is the general ' between a planet speed and I its average distance from the sun . The planet Uranus is about 300 ) 600 300 from the sun ( Average from sun whether its speed IS greater or less than ( millions of kilometers ) Jupiter speed . Explain your answer 5420

Uranus AU Modern View of the Solar System Today . people talk the solar system rather than the . This that people the that Earth and the other the sun . Components of the Solar System Since ' time , our knowledge of the solar has increased . Galileo knew the planets that ancient ( had ' I ) Jupiter . and Saturn . Since time . have two ) ax well as Pluto . is no longer to he . The vairy greatly in size and . They also in , ruin thi sun . tilt of their axis , and other ( I ) provides detailed data ! of the , All of planets and ) i moon is it that i i . also id other in the solar ) such as and . Today we know that the solar system consists of the sun . the planets and their moons , and several kinds of smaller objects that revolve around the sun . Measuring Distances in the Solar System The distances the sun and the planet are very large compared to that arc ( a , I ' distances within the solar using ) a units . astronomical unit . or AL . age the sun ( about lit ) million ' in you can set that Saturn distance from the sun is AU . This that , on . Saturn ix ! farther the sun than . nude rig What is an astronomical unit ! Neptune AU Pluto AU active Fur Solar System Visit ( Web ( ode ( Calculating If you know an distance from the sun in AU , you can convert this distance to kilometers hy multiplying it by . Recall that IAU million . For example , Ceres is the largest of a group of objects called asteroids . Ceres orbits the sun at an average distance of AU . How far is Ceres from the sun in kilometers ?

Between the orbits of which two planets does Ceres orbit lie ?

How far is Ceres orbit from Earth orbit in both AU and kilometers ?

543 Exploring the Solar System Galileo used telescope to observe distant parts solar system from surface . Astronomers today still use telescopes on Earth . but also telescopes in space to gain 31 better view of the universe beyond Earth . The sun is the source light in the solar system . You learned in the lust that the moon does not produce its own light . Rather . you can see the moon because its sunlight . Similarly . the planets and moons of the solar do produce their own light . they do give oil in the of heat . Thu planets and moons are visible because sunlight from their . in addition to observations made with telescopes . scientists have sent to the moon and launched numerous space probes in the far reaches solar , Our understanding oi the solar continues to grow every day . Who knows what new discoveries will be in your lifetime ! FIGURE Saturn This image at Saturn and its rings was taken by the Cassini spacecraft , which is currently exploring Saturn and its moons . EA Bill Assessment Section Vocabulary Skill Greek Word Origins Huw knowing I word origins help remember tho ' and ?

Reviewing Key Concepts a . Explaining What are the . and heliocentric systems ?

What Ul ' up the solar system ?

Listing hat are the , in order distance from the sun ?

Interpreting Diagrams Use Figure in find the planet with Earth . nun . Comparing and Contrasting How was model at the ! in from model ?

Draining Conclusions What ' by do , an magma ( milieu support the heliocentric model ?

between and Game , about Applying Concepts People say the sun of the rises in the east . crosses the sky . and sets in west . is this literally ?

Explain . lunar Interpreting Data How did use ' data ?

systems . which would each scientist favor ?

What evidence could each offer to support his view ?

Do you think that one could convince the other to change MIT . Describing What did discover mind ?

Ugg mug young 11 the shapes of the planets orbits ?

of gun , How did and the method ?

El ! El Students know the role of gravity in farming and maintaining the shapes ol planets , stars , and the solar system . Students know that the Sun is one of many stars the Milky Way galaxy arid that Stars may diller ' size , temperature . and color How does the sun energy ?

What are the layers ol the sun interior and the suns atmosphere ?

What features on or above the sun ur ( Key Terms nuclear fusion ' core radiation zone convection zone ' I corona solar wind I sunspot prominence solar The Sun How Can You Safely Observe the Sun ?

I . lamp pair of binoculars to a ring stand as shown In the photo . Cut a hole in a by sheet of thin cardboard so that it will fit over the binoculars , as shown in the photo . The cardboard should cover one lens , but allow light through the other lens . Tape the cardboard on securely . Use the binoculars to project an image of the sun onto a sheet ol white paper . The cardboard will shade the white paper . Change the focus and move the paper back and forth until you get a sharp image CAUTION Never look directly at the sun . You will hurtyour eyes ifyou do . Do not look up through the binoculars . It Over Observing Draw what you see on the paper . What do you see on the surface at the sun ?

you are aboard a approaching the solar system from afar . Your first of the solar system might that it consists ( Ila star , the sun . with tiny orbiting around it . Your first be ( ill . In lain . sun accounts for percent of the solar system total mass . i a til its mass . sun force throughout solar . Although force decreases rapidly with distance . it is strong enough to hold all the planets and in orbit . Gupta 545

' Energy from the Sun Unlike Earth , the sun does not have solid surface . Rather , the sun is a huge hall of ionized gas , or plasma . throughout . About of the sun mass is hydrogen . About of the sun mass is helium . There are also small Web ( ode amounts of other elements . Nuclear Fusion The sun shines brightly . providing energy needed for life on Earth . But how is this energy produced ?

Early scientists hypothesized that the sun produced its energy through a chemical reaction , such as burning fuel . However , if this were the case . the sun would have lasted for just a few thousand years before its fuel ran out . Since the sun is actually about billion years old , this hypothesis is clearly wrong . In the early . scientists discovered the real source of the sun energy . The sun producer energy through fusion . As shown in Figure in the process of nuclear fusion . two atomic nuclei combine . forming a larger . more massive nucleus and releasing energy . Within the sun , hydrogen atoms join together to form helium . Nuclear fusion am occur only under conditions of extremely high pressure and temperature . Such conditions exist in the sun core , or central region . The temperature within the core reaches about million degrees Celsius . high enough for nuclear fusion to take place . The total mass of the helium produced by nuclear fusion is slightly less than the total mass of the hydrogen that goes into it . The missing mass is changed into energy . It moves slowly ward from the core . eventually escaping into space . Some of this ' energy reaches Earth , where you experience it as light and heat . During nuclear fusion . two nuclei and fuse . Small nuclei may be nuclei ( A ind ) collide and fuse , tanning a nucleus with a higher atomic number ( Two larger nuclei collide and fuse . forming a still larger nucleus ( 5450

Forces In Balance fusion in the sun core produces an incredible amount of energy . This energy causes gas ions within the sun to move very fast . generating a tremendous pressure pushing outward from the core . This pressure would cause the sun to explode if it were balanced by an equal and opposite force . This opposing force is the surfs own gravity , which pulls matter . The weight of matter pressing inward and the outward pushing pressure are balanced throughout the sun . As a result . the sun is stable . The sun will remain stable as long as there is a steady energy source within it . Astronomers estimate that the sun will be stable for another billion years or so . The Sun Interior ' Like Earth . the sun has an interior and an atmosphere . The Flaunt sun interior consists of the core . the radiation zone . and pom , the zone . Gravity and outward pressure are balanced throughout the sun . The Core As you have learned . the sun energy is produced in its central core . Here , the temperature and pressure are so high that nuclear fusion can take place . The sun care has a , ter of about ! more than 30 times Earth diameter . force of gravity strongest ?

The Radiation Zone The energy produced in the sun core moves outward through the middle layer of the sun interior . the radiation zone . The radiation zone is a region of very tightly packed gas where energy is transferred mainly in the form of mung radiation . Because the radiation mine is so dense , sun energy can take more than yam to move through it . The Convection Zone The convection none is the most layer of the sun interior . Hot gases rise from the bottom of the convection zone and gradually cool as they approach the top . Cooler gases sink , forming loops of gas that move energy toward the suns surface . What is the convection zone ?

to The Sun Corona During a total solar eclipse . you can see light from the corona , the outer layer of the sun atmosphere . around the dark disk of the moon . Viewing Sunspots You can observe changes in the number of sunspots . Make a data table to record the number of . Decide on a time to study sunspot each day . Wew the sun image in the way in the Discover activity in this section . Never look directly at the run . You will hurt your eyes if you do . Make and record your observations . Interpreting Date How much did the number of sunspots change lrom day to day ?

sunspots you see each day . The Sun Atmosphere The sun atmosphere includes the photosphere , the . and the corona . Each layer has unique properties . The Photosphere The inner layer of the sun is called the ( tuh ) The Greek word photos means light , so means the sphere that gives visible light . The sun does not have a solid surface . but the gases of the are thick enough to he you look at at typical of the sun , you an looking at the photosphere . it is considered to be the sun surface layer . The Chromosphere During a total solar eclipse . the moon blocks light from the . The photosphere no longer produces the glare that keeps you from seeing the . outer layers . At the start and end of a total eclipse . a dish glow is visible just around the photosphere . This glow comm from the middle layer of the sun atmosphere . the mull ) The Greek word means color , so the is the color The Corona During a total solar eclipse an even fainter layer of the sun becomes visible . as you can see in Figure ( This outer layer . which looks like a white halo around the sun . is called the corona . which means crown in Latin . The corona extends into space for millions of kilometers . It gradually thins into streams of electrically charged particles called the solar wind . During whet event could you see the sun corona ?

Features on the Sun For hundreds of years , scientists have used telescopes In study the sun . They have spotted a variety of features on the surface . Features on orjust above the sun surface include sunspots , prominence and solar flares . Sunspots Early observers noticed dark spots on the suns surface . These known as sunspots . Sunspots look small . But in fact . they can be larger than Earth . Sunspots are areas of gas on the suns surface that are cooler than the gases around them . Cooler gases do give oil much light as hotter es . which is why sunspots look darker than the rest of the . Sunspots seem to move across the surfs surface , showing that the sun rotates on its axis . just as Earth does . The number on the sun varies over period of about I I years .

The Layers of the Sun Prominence Corona ( extending into space ) thin layer ) visible surface ) Solar flare FIGURE 12 Auroras such as this can near Earth poles when of the strike gas in upper atmosphere ) usually ( in groups . Huge . reddish loops of gas ( link parts . group is near the edge ot the sun as seen from Earth . these loops lie ( over the edge sun . Solar Flares ( thi loops in regions , large ut energy . The energy heats gas on the sun to millions ( causing the gas to erupt into space . These eruptions are solar . Solar Wind Solar can greatly ' i ' the solar wind the , resulting in an increase in the of particles Earth upper ' Earth and magnetic block these particles . mail the North turd South . the particles can enter Il . where they create currents that cause gas in the ' result is rippling of light in thi sky called . Solar wind particles also Birth field . causing . disrupt radio , and . ion . storms ( 411 also power in . What is a prominence ?

Section Assessment Vocabulary Skill Greek Word Origins ( origins In ( lli and . Reviewing Key Concepts MINT , a . Defining What is HINT Explaining is thi sun ?

steps in HINT , the process of nuclear within the sun . mutt a . Listing list the surfs interior and , starting from the center . IE I ) which of the sun layers ' ilk light ?

all Relating Cause and Effect Why is it to sunk Earth ?

we ' a 41 . Reading . I . Describing ) i ( or ) the sun . Relating Cause and Effect hy do louk darker than the of the sun ?

Symbols As the source of heat and light , the sun is an important symbol in many cultures . with family members , look around your home and neighborhood for illustrations of the sun on signs . clothing , and in artwork . which parts of the sun atmosphere do the illustrations show ?

Stormy Sunspots Annual Sunspot Numbers . sunspot sunspot Number Number 683 em 1974 How are magnetic storms an Earth related to 94 sunspot activity ?

925 Skills Focus graphing , interpreting data Materials 1002 10440 graph paper am ' Storm Days Procedure 60 . Use the data in the table of Annual Sunspot 50 Numbers to make a line graph ot sunspot ' activity between 1972 and 2002 . On the graph . label the Use a scale with intervals , from 1972 to 2002 . 20 . Label the sunspot Use a 10 scale of through 160 In intervals or . Graph a point for the sunspot Number for 9970 75 go 35 go 95 00 each year . Vear . Complete your graph by drawing lines to connect the points . I Communicating Suppose you are an and conclude neer working for an electric power company . Write a brief summary of your analysis of . Graphing Based on your graph , which years had the highest Sunspot Number ?

The sump dam Flam me between sunspot number and electrical en ' disturbances on Earth . Interpreting Data How often does the of maximum and minimum activity repeat ?

Mofe to . Interpreting Data When was the most recent , pane , of su spo you , predict the number of peaks you would expect in minimum the next 30 years . Around whith years would you . Inferring Compare your sunspot graph with expect the peaks to occur ?

the magnetic storms graph . What relationship can you infer between periods of high sun spot activity and magnetic storms ?

Explain . chapter 14 Fo Students the appear ance , general , relative position and size . and motion of onions in the solar system . ing planets , planetary satellites . comets . and asteroids . What characteristics do the inner planets have in common ?

what are the main that distinguish each of the inner Key Terms I terrestrial planets I greenhouse 552 The Inner Planets , Standards How Does Mars Look From Earth ?

Work in pairs . On a sheet of paper , draw a circle 20 across to represent Mars . Draw about small lines , each about long . at random places inside the circle . Have your partner look at your drawing of Mars from the other side of the room . Your partner should draw what he or she sees . Compare your original drawing with what your partner drew , Then look at your own drawing tram across the room . Think It Over Observing Did your partner draw any connecting lines that were not actually on your drawing ?

What can you conclude about the of descriptions of other planets based on observations from Earth ?

Where could you whose has almost entirely leaked away into space ?

How about planet whose face is hot enough to melt lead ?

And how about planet with higher than any on Earth ?

where could you find at planet with ' til water brimming with and other life ?

These are descriptions of the four closest to the sun , known the inner planets . Earth and the three other inner . Venus . and ' more similar to than they the live . four inner planets are small and dense and have rocky surfaces . The inner planets are often called the terrestrial planets , lrom the Latin . which . Figure data about the inner planets . Earth As you can ' in Figure 14 . Earth has crust . a mantle . and core . The crust includes the solid , rocky surface . the crust is the mantle , layer of hot molt rock . this hot rises to the sur lilac . Birth has it ' manic ul mainly iron and nickel . The outer cure is liquid . but the inner core is solid .

The Inner Planets Size Period of Average Distance Plant ( Rotation From Sun Diameter mans ( UM div ! 59 Venus 24 Earth to Mats i FIGURE 13 Water is unique in our solar system in having The inner planets take up only a small liquid water at in surface . In fact . most at Earth sulfate , SOL SY 71 ) percent . is covered with water . our planet ' a ' ale be Waler of I Earth has suitable range for water to exist at liquid . gas . or solid . Water is in Earth su , ing it down and its over time . Atmosphere Earth has enough gravity to hold an In mos ! These gases make up , which extends mure than 100 kilometers above its . Other planets in the solar system have too . but only has an atmosphere that is rich in oxygen . The Oxygen you need to live nukes up about 20 percent . Nearly all the real is nitrogen . willi small of other gases such as argon and carbon dioxide . The atmosphere also includes varying amounts of water in the form of a gas . Water in 21 form is called water vapor . haunt me ! We Earth Earth has a solid . rocky surface Interpreting Diagrams What are Earth three mam ?

What ( we gases make up most of Earth Checkpoint ammo is 55 Size of Mercury ( to Earth mun 15 This image of Mercury was produced by ( series of smaller images made by the Manner space probe . Interpreting Photographs How is Mercury different fram Earth ?

Mercury Mercury is the smallest terrestrial and the plane ! lo the sun . Mercury is not larger moon and has no ' ix probably made up of the dense metal iron . Exploring Mercury slim lo the mu , it is hard 10 sec from Earth . Much know about ( from single , I ! by in and , Tun lu nur ' The lint ! ME . is to go into around in 201 Show that ' many plains and on its The of Mercury ' has ' for billions If ' haw fur , writers . and Bach and . Mercury Atmosphere Mercury has . high gas lo ' fem . is small , il gravity is aL . Fast moving ( can ) small ul and ( her ( ur ) I ' LlI ' is ( I , range than any planet in the solar system . It is so do to sun that during the day , the facing the sun . Hecause Mercury has , at nigh ! its imu , ils drops below ( Compare daytime and nighttime temperatures on Me ,

clouds cover the surface . 16 Venus Mons is the volcano on Venus Blue regions are flat plains covered by lava flows . This figure combines images of Venus taken from space with a camera ( left ) and radar ( right ) The camera image shows Venus thick atmosphere . Radar is able to penetrate Venus clouds to reveal the surface . hath Images are false color . Venus You can sometimes see Venus in west just after sunset . When Venus is visible in that part of the sky . it is known as the evening star , though of course it really is A star at all . At other times . Venus rises in the cast ( the sun in the ing . Then it is known as the morning star . Venus is so similar in size and mass to Earth that it is times called Earth density and internal structure are similar to Earth . But . in other ways . Venus and Earth are very different . Venus Rotation Venus takes about Earth months to revolve around the sun . It takes about months for Venus to rotate once on its axis . rotates so slowly that its day is longer than its year ! rotates from east to west , the opposite direction lrom most other planets and moons . Astronomers that this unusual rotation was caused hy a very large object that struck Venus billions of years ago . Such a collision could have caused Venus to change its direction of rotation . hypothesis is that thick could have altered iLs rotation . Size at Venus compared to Earth Go Online ( cab . Quote ! 14 555 for Links on the planets Welt Code

Try Activity Greenhouse Effect How can you measure the effect of a closed container on temperature ?

Carefully place a thermometer into each of two glass jars . over one jar with cellophane . Place both jars either in direct sunlight or under a strong light source . Observe the temperature of both thermometers when you start . Check the temperatures every minutes for a total of 20 minutes . Record your results in a data table . Compare how the temperature changed in the uncovered jar and the covered jar . What do you think is the reason for any difference If ! the temperatures of the two jars ?

Which jar is a better model of Venus atmosphere ?

Hum 17 Scientists used radar data to develop this computer image of the giant volcano Moat Maria The of the mountains are exaggerated to make them stand out . Venus Atmosphere atmosphere is so thick that it is always cloudy there . From Earth or space . can only a smooth cloud . The clouds arc made of sulfuric acid . you could stand on surface , you would quickly be by the weight of its . The of atmosphere is 90 times greater than the pressure of Earths . You couldn on because its is . is closer to the sun than Earth is . it receives more solar energy than Earth does . Much of this radiation is by clouds . However . some radiation ' a ' surface and is later given off as heat . Thu carbon in traps heat so well that has the hottest ul any . Al its average surface is hot enough to melt lead . This trapping of heat by the atmosphere is tho greenhouse effect . Exploring Venus Many space have visited . The probe to land on the surface and send back data . landed in . survived for only few minutes because of the high temperature and pressure . Later probes were mum durable and sent and data back to . The probe reached Venus in , carrying radar instruments Radar works through clouds . so was able to map nearly the entire ' The data firmed that is covered with rock . surface has many volcanoes and broad plains by lava . aw ) what are Venus clouds made or ?

Mars is called the red planet . When you see it in the sky , it has a slightly reddish tinge . This reddish color is due to the down of rocks . which creates a rusty dust that much of Mars surface . Mars Atmosphere The atmosphere of Mars is more than 95 percent carbon dioxide . It is similar in composition to atmosphere . but much thinner . You could walk on Mars . but you would have to wear an airtight suit and carry your own oxygen . like in scuba diver . Mars has few clouds , and they are very thin compared to clouds on Earth . Mars transparent sphere allows people on Earth to view its surface with a telescope . Temperatures on the surface range from I to 20 . Water on Man In , an Italian astronomer named Giovanni ( sky ah puh REL ) announced that he had seen long . straight lines on Mars . He called them auntie , or channels . In the 18905 and early . Percival Lowell , an American astronomer . convinced many people that these lines were canals that had been built by intelligent Martians to carry water . Astronomers now know that was . There are no canals on Mars . Images of Mars taken from space do show a variety of features that look as if they were made by ancient streams . lakes , or . Then are huge canyons and features that look like the remains of ancient coastlines . Scientists think that a large amount of liquid on Musk surface in the distant past . infer that Mars must have been much warmer and had a thicker atmosphere at that time . At present . liquid water can not exist for long on Mars surface . Mars sphere is so thin that any liquid water would quickly turn into a gas . So where is Mars water now ?

Some of it is located in the planet two polar ice caps , which tain frozen water and carbon dioxide . A small amount also exists as water vapor in Mars atmosphere . Some water vapor has probably escaped into space . But think that a large amount of water may still be frozen underground . is ( 39 Size of Mars compared to Earth ta Mats Because of its thin atmosphere and its distance from the sun , Mars is quite cold . Man has ice ups at both poles . Inferring Why is it easy to see Man surface from space ?

Output 14 557 Video Trip nI ( School The Solar System Activity Remote Control How hard is it to explore another planet by remote control ?

Tape a piece of paper over the front of a pair of goggles . Have your partner put them on . Walk behind your partner and direct him or her to another part of the room . CAUTION Do not give directions that would cause your partner to walk into a wall ora comer , trip on an obstacle , or bump into anything . Trade places and repeat Steps and . Drawing Conclusions Which verbal directions worked best ?

How quickly could you move ?

How is this activity similar to the way engineers have moved rovers on Mars ?

How fast do you think with a rover could move ?

SSI Seasons on Mars Because Mars has a tilted axis , it has sons just as Earth docs . During the Martian winter . an ice cap grows larger as a layer of frozen dioxide covers . Because the northern and southern have opposite seasons . one ice cap grows while the other one shrinks . As the seasons change on the dusty surface of Mars , storms arise and blow the dust around . Since the dust is blown off some regions . these regions look darker . A hundred years ago , some people thought these regions looked darker because plants were growing . Astronomers now realize that the darker color is often just the result of windstorms . Exploring Mars Many space probes have visited Mars . The lirst ones seemed to show that Mars is and covered with craters like the moon . Recently . two new probes landed on Mars surface . Spirit and Opportunity rovers explored opposite sides planet . They examined a variety of rocks and soil samples . At both locations , the rovers found strong evidence that liquid water was once present . The European Space Agency Mars Express probe . clear evidence of water ( ice ) However . the Mars lander failed . Volcanoes on Mars Some regions of Mars have giant volcanoes . Astronomers see signs that lava flowed from the volcanoes in the past , but the volcanoes are not currently active . However , volcanic eruptions may have occurred in some areas within the past few million years . Olympus Mom on Mars is the largest volcano in the solar system . It covers a region as large as the state and is nearly three times as tall as Mount Everest , the tallest mountain on Earth !

! 19 As the large photo shows , the surface of Mars is rugged and rocky . Mars has many large Mars Moons Man has two very small . Th ?

Mans ( inset ) uses about 27 moons , Phobos , the larger moon , is only 27 In , about the distance car can travel on the highway in in , 20 minutes . is wen smaller , only in ter . Like moon . Phobos and are covered with craters . which is much to Mars than is . is slowly spiraling down toward Mars . Astronomers predict that Phobos will smash Mars in about 40 million years . i Hunting How many moons does Mars have ?

whu an their ?

section Target Reading Skill ( rule your outline of A this section to ' following . Writing In Sue ( Reviewing Key Concepts Inn ! Select on . of I . Listing List the four planets in order of sin . from the Inner planets other than smallest lu largest . I travel brochure for ii ?

I ) Comparing and Contrasting How are the inner your selected , similar In one ?

bask FEB and descriptions of UT a . Describing Describe an important ul DISCS at . Also include I each inner planet . few sketches or to 90 . I . Comparing and Contrasting ( the ' of the four . Rotating Cause and Eftect Venus is much from . um than Mercury Is Yet on Venus surface are much higher than those on Mercury . Explain why 14 559

Science and , Space Is It Worth the Cost ?

Imagine that your spacecraft has just landed on the moon or on Mars . You spent years planning for this moment . craters . plains , and distant mountains stretch before you . Perhaps in group of has already begun construction ofa outpost . You check your and prepare to step out onto the rocky surface . la such a trip likely ?

Would it be ?

How much is space really worth to human society ?

Scientists and public have already started to ) Space exploration can help us learn more about the universe . But exploration can be risky and expensive . Sending people into space costs billions and risk the lives of . How can we balance the costs and of space exploration ?

Moon landing A lander The Issues ' Should Humans Travel Into Space ?

that Neil mill on the moon in ) Wax one in the great moments in , I him to keep people alive in pore has led to in lili . to lure ' What Are the Alternatives ?

Space exploration can involve project to on the moon or . can more ! near . such is the ' Instead sending people . we spate ! like to .

Lunar Module this artwork shows I futuristic that may one any to lhE moon and Mars The as , rover and for astronauts . Is Human Space Exploration Worth the Cost ?

travel into ' that only people can collect certain kinds of that ' ur human ' hart Earth . But no unc ' in provides information more than that he done Earth . ul human space think that other ( Iced arc mute . Ont Status ry ' time you put money turn the space . there is dime that wont be unr ur ' Lunar Outpost A on th moon is thus artwork Such a may harvest oxygen from . Identify the Problem . Analyze the Options a Solution In your own words , list the ) and of il chart of In exploration to the or . unly . and and ugh of thew ?

who has to Vote ( In new budget . is amount of to . so mu haw lu arr ( list 11 ! yuur top ten . your . HI . It mu For More on spare Exploration Visit . Web Code Game 14 561 it Students the appear ance , general composition , relative and size , and motion of in the solar system . ing planets . planetary satellites . comets . and asteroids What do the gas giants have in ( what distinguish of the outer planets ?

Key gas giant ring 5616 The Outer Planets . la How Big Are the Planets ?

The table shows the diameters of the ' am . outer planets compared to Earth . For example , Jupiter diameter is about 53 ' times Earth diameter . Measure the diameter of a quarter in millimeters . Trace the quarter to represent Earth . man , 40 . If Earth were the size of a quarter , calculate how large Jupiter would ' be . Now draw a ( to represent Jupiter . Repeat Step for of the other planets in the table . Think Over Classifying List the outer planets in order from largest to smallest . What is the largest outer planet ?

imagine you are in spaceship approaching . is very from the ' The most ) ix great size . is so large that more than Earths could til within it ! As your ?

sphere . you encounter thick . colorful bands of clouds . you sink at and . of and helium . ii the enormous pressure of this does not crush your ship . reach an incredibly deep in of liquid hydrogen arid helium . But where exactly is ' a ?

there is ti solid surface . Like the other giant planets . has no real surface . just a core ( the planet . An illustration of the spare probe Galileo approaching the atmosphere of Jupiter .

Neptune The Planets and Pluto of Anna ) Sun woman ' Plum ( Em ?

days ) AU ) 041 52 12 53 Saturn 29 072 84 27 . 494530 I 300 154 Pluto 64 392 Gas Giants and Pluto and thes the sun Arr called the planets . The four outer . and much and more than Earth , and they do not have solid surfaces . planets art my large . diet are gas giants . 10 provides about ' It includes ! which is now . like sun . giants have ) mainly , so gas giants exert much force than the terrestrial planets . Gravity giant ' gusts , xi ) the gin . much ! the and helium is actually in liquid form because of pressure the planets . Thu outer layer are cold because of great from the sun . Temp ' greatly within the planets gas giants haw 111411 ) In addition . til the gas giants is Ivy a nut at rings . A ring a thin disk of small particle ice and rock . The outer planets are mu ( farther apart than The inner planets . Pluto is now ( to be a . Note that planet and distances are not drawn to sale . Observing Which has the most moons ?

Go 14 563 For Marv an the Visit ( Web ( ode helium gas Hydrogen and Jupiter is the largest and most massive planet . enormous mass dwarfs the other planets In fact , its mass is about times that of all the other planets combined ! Like all of the gas giants . has a thick atmosphere made up mainly of hydrogen and helium . An especially interesting feature of atmosphere is its Great Red Spot . a storm that is larger than The storm swirling winds blow hundreds of kilometers per hour . similar to a hurricane . But hurricanes on Earth weaken quickly as they pass over land . On . there is no land to weaken the huge storm . The Great Red Spot . which was first observed in the . shows no signs of going away soon . Jupiter structure Astronomers think that , like the other giant planets . may have a dense core of rock and iron at its center . As shown in Figure ! a thick mantle of liquid hydrogen and helium surrounds this core . Because of the crushing weight of atmosphere , the pressure at ter core is estimated to be about 30 million times greater than the pressure at Earth surface . Jupiter Moons Recall that Galileo discovered four largest moons . These moons , which are highlighted in Figure 22 , are named lo ( EYE oh ) Europa . Ganymede , and . All four are larger than own moon . However . they are very different from one another . Since Galileo time . astronomers have discovered dozens of additional moons orbiting . Many of these are small moons that been found in the last few years thanks to improved ) What is composed on , Home 21 Jupiter Structure Jupiter is composed mainly of the ' elements hydrogen and helium . Although Jupiter is often called a gas much of it is actually liquid . Liquid ' i es Comparing and Contrasting How does such as water the structure differ from that and methane ofa ?

Rocky core 600 22 Jupiter Moons Tim . a our moors , These re not . tev ) JI ( surface as i ( and covered with ( Astronomers suspect that Europa crust covers an ocean ! liquid water underneath This illustration shows Europe icy . A Io is covered with large . volcanoes . An eruption oi sulfur lava can be seen near the bottom of this photo . Sulfur gives Io its unusual colors . Ganymede is the largest moon in me solar system . is large ! than either Mercury or Plum

13 Exploring Saturn The probe exploring Saturn and its moons . Observing Why hard to see Saturn rings when their edges arr facing Size of Saturn to Earth man Making Models . Use a loam sphere in diameter to represent Saturn . Use an overhead to represent Saturn rings Cut a circle 18 ( in diameter out of the transparency . Cut a hole in diameter out of the ( enter oi the , Stick five toothpick into Saturn , spaced equally around its equator . Put the transparency on the toothpicks and tape it to them . Sprinkle baking soda on the transparency . Use a peppercorn to represent Titan . Plate the peppercorn 72 away from Saturn on the same plane as the rings . What do the particles of baking soda represent ?

5660 Saturn The in ' is Saturn . uI that . has 21 thick ' up ) and ( atmosphere also contains clouds and storms . hut they are less than on Jupiter . is only is than that . Saturn Rings hen first looked at with ( mold to ) Ul ( mic . he know what it . rI ( Liter , an using bullet , LU , Saturn had rings around it . rings are not solid . tilt ol ice and , in its own . Saturn has most spectacular rings of any planet . it though rings and that ' arc divided catch ' i ' i . The ' that ot Ul ) rings is into many . rings are and thin . like a compact disc . Saturn Moons , moan . than the planet ' was in 065 hut was ( hy . The that ' light pa through it . Foul are mull over ( in . Reading , What are Saturn rings made on

, 24 Size ! Uranus ( Uranus ( fem The tame image ! was taken by the Snare . most other Uranus . rotates ( rum top to ! i ' uh um time the 01 Earth . it is still muth than ' I ) tram the ! mam . so it much , looks of in I ( I ike the gas giant ) is At group ut thin . tings . than urn ' Discovery of Uranus In I , lint new . lime . met ' Ill ) the ky that did not like star . At I he it he . but it man pawn ! he planet het Hie ' of active whit . Exploring Uranus ( I at , ind sent i ( view ! that . hum ' even these few to that ( in IT ( axis of is tilted at an angle of about 90 degrees the . Viewed it um Eat th . i , up to ol side In . the ' of the tin , and mute li ' think that ago ' mux ( iI . side . Uranus Moons Hum I tin ' It ) The ( have hit the . ti ' their . that has erupted from inside each Ill that hail Item , RA , I at total in at . Who Uranus ?

Chapter 14 561 25 Neptune The Great Dark Spat was a giant storm in Neptune atmosphere . White , made of methane ice ( can also be seen in the photo Size of Neptune compared to Earth Circumference To calculate the circumference of a circle . use this In the , and is the ( If ( lE radius . which is the distance from the center of the circle to its edge , The same formula can be used to calculate the circumference of planets . which are nearly spherical . Neptune radius at its equator about . Calculate its circumference . Practice Problem radius is about . What is its circumference ?

Neptune the sun than Uranus . trays , the two ' twins . Titty AIR in silt and calm . Neptune is cold . blue planet . Its atmosphere contains visible clouds . think that . in ligure 15 , is ) to heat up . this energy rims ' it produces ( and in ' Discovery of Neptune was as result ut iJ . noted that was not the orbit predicted for it . They ( called that this at an . orbit . By , in and ' had calculated the of this unseen . Shortly thereafter , an saw an unknown object in Alt . Exploring Neptune In 198 ) i i by and it ( Dank Spot about the aim at birth . like the Great Red Spot on . the Great lurk Spot was giant . But the sturm drain ! lung . It int wars ( that the Dark Spot gone . Other . spots and regions at ) un ) gu . Neptune Moons ) have ill moons Neptune . The moon is Triton . which has thin re . The ) images show that the region near south pole is covered by nitrogen ice . they could see Neptune , what evidence led i to that it existed !

Size oi Pluto compared to Earth Pluto is very Ilia gas . Pluto has a solid surface and is much smaller and denser than the outer . In fan . Plum is smaller than . Pluto is llI ( of a of rock and la . has three . The of these . Charon . is more than ' Pluto Orbit is so fair sun that ii ( around sun only i ' Earth i ' orbit is very , it to this sun on part of its orbit . Dwarf Planets . was ( lo ninth planet in nur ' in he of an ' ul ils small size and unusual . Then . in rec years . many in Ne Some of these were ro Plum um and thaw . The illustration above shows in . I ' is mum ( lawn ) and , moon larger and farther from than ' lo Charon , Charon is more than half create a new class of objects called . A dwarf . is round and sun . But unlike planet , Plum and two other . 16 . i . Assessment vi , Target Reading Create Outlines an HINT your outline in this . of each miter planet that helps ( I Pluto ?

in ii . Comparing and Contrasting Him is Reviewing Key Concepts ' How an gas giants In ' om ?

HINT . Explaining Why do all gas giants ' list . iii ' ul sin . Iu largest . Comparing and Ih of terrestrial planer grin giant . use dill ihe gi ?

Classifying ) rI ( nu as A dwarf ?

Practice . Jupiter radius is about What is its circumference ?

Design Your Own Lab Speeding Around the Sun Problem How does a planet distance from the sun affect its period of revolution ?

Skills Focus making models , developing hypotheses . designing experiments Materials string , I ( tube . in meter stick weight or several washers rubber stopper or watch with second hand PART Modeling Planetary Revolution . Copy the data table onto a sheet of paper . Procedure Data of Revolution . am Trial . Make a model of a planet orbiting the sun by threading the string through the rubber stop per ie the end of the string to the main part of the string . Pull tightly to make sure that the knot will not become untied . Thread the other end of the string through the plastic tube and tie a weight to that end . Have your teacher check both knots . 5700 Pull the string so the stopper is 20 ( away from the plastic tube . Hold the plastic tube in your hand above your head . Keeping the length of string . swing the rubber stopper in a circle above your head just fast enough to keep the stopper moving . The circle represents a planet orbit , and the length of string from the rubber stopper to the plastic tube represents the distance from the sun . CAUTION Stand away from other students Make sure the swinging stopper will not hit students . Do not let go of the string . Have your lab partner time how long it takes for the rubber stopper to make ten complete revolutions . Determine the period for one revolution by dividing the measured time by ten . Record the time in the data table . Repeat Step two more times . Be sure to record each trial in a data table . After the third trial . calculate and record the average period of revolution .

Designing an Experiment More to Explore . Write your hypothesis for how a planet ?

how ' of would be by might period of revolution . Then , using a ( hanging In damn ! om me stopper with a different mass , modify the activity to test your hypothesis . Before you your . Design an experiment that will enable you to stopper have your gamer ( heck you . test your hypothesis . Write the steps you plan to follow to carry out your experiment . As you design your experiment , consider the following factors What different distances will you test What variables are involved in your ment and how will you control them ?

How many trials will you run for eath distance . Have your teacher review your plan . After your teather approves your plan . carry out your experiment . Analyze and conclude . Making Models In your experiment , what represents the planet and what represents the sun ?

Making Models What force does the pull on the string represent ?

Interpreting Data What happened to the period of revolution when you changed the distance in Pan ?

Did your experiment prove or disprove your hypothesis ?

Drawing Conclusions Which planets take less time to revolve around the closer to the sun or those farther away ?

Use the model to support your answer . Designing Experiments As you were design ing your experiment , which variable was the most difficult to control ?

How did you design your procedure to control that variable ?

Drawing Conclusions Did you obtain the same results in all three trials ?

What do your results indicate about the accuracy of your data ?

Write a brief summary of your experiment for a science magazine . DE your hypothesis , procedure , and results in one or two paragraphs . 14 571 Standards Focus Students know the an ( general ( relative position and , and motion of objects in the solar system , planets , planetary satellites , comets . and asteroids what are the characteristics of comets ?

where are most asteroids What are and how do they ! Key Terms comet ' coma I nucleus I Kuiper belt I Don cloud asteroid I asteroid belt I I meteor I meteorite 27 Structure ot a Comet The main parts of a comet are the nu ( the coma . and the tail The nucleus is deep within the coma . Most comets have two bluish gas tail and a dust tall . 571 Comets , Asteroids , and Meteors Standards Which Way Do Comet Tails Point ?

I . Form a small ball out at modeling clay to represent a comet . Using a pencil point . push three lengths of string into the ball . The strings represent the comet tail . Stick the ball onto the pencil point . as shown . Hold the ball about I in front of a fan . The air from the fan represents the solar wind . Move the ball toward the tan , away from the tan , and from side to tide . CAUTION Keep your fingers away from the fan blades . Think It Over Inferring How does moving the ball affect the direction in which the strings point ?

What determines which way the tail of a comet points ?

watching ti cosmic collision ! exactly what in 1994 . The you . Carolyn Shoemaker and David comet that had broken into pieces near . the passed again , the into On Earth , many lal I lu View til the huge were ais large as Earth ! As this example shows . the sun . planets . and moons the only objects in the solar system . There are also many smaller objects through the solar . These are as comets , asteroids .

Comets ( 11 ' But what . comet ' the ul . are loose collections ice . dust , and small rocky particles whose orbits are usually very long . narrow ellipses . A Head ( low , In . turns the icy into . gas and ( and dust ' 21 coma . 27 1131114 dull the 11 ! ul up ul . A Comet Tail As up . 11111 ' its gas . in Gnu . gas dust . The mil the 11111 , As 111 . he ( NI long ' Origin of Comets ! one at ' Ilk ( lULl . The Kuiper belt is A , that ' orbit to about . Oort cloud i ( ul comets that surrounds the . about I , What is the Our ! loud ?

ca . 11311 . Link comers and Visit Web ( ode Flaw 13 Comet Most revolve around the sun in very long , narrow Gas and dust form as the tome ! the sun . a comet ?

Comet 14 573 73 Try This Activity An estimated 300 tons of material from space fall on Earth each day . Much of this is . tiny . dust sized meteorites . To gather magnetic . tie a string to a small , round magnet and place the magnet in a plastic bag . Lower the magnet close to the ground as you walk along sidewalk cracks , drain spouts , or a parking lot . To gather nonmagnetic and magnetic , cover one side of a few microscope slides with petroleum jelly . Leave the slides outside for several days in a place where they wo be disturbed . Use a microscope to examine the materials you have gathered . Any small round spheres you see are . Estimating Which technique allows you to gather a more complete sample of micro meteorites ?

were all the particles that were gathered in Step ?

How could you use the method described in Step to estimate the total number of that land on Earth each day ?

574 Asteroids and , discovered four between the orbits of Mars and . They named the objects Ceres . and Vesta . Over the next , astronomers found 301 ) more . These rocky objects . called asteroids , are on small and Inn to be ( I ( planets . Most asteroids revolve around the sun in circular orbits between the orbits of Mars and Jupiter . This region of the solar . in Figure 29 , is called this asteroid belt . Astronomers have discovered more than , and they are more . Most asteroids are than a kilometer in diameter . Only ( Zeros , and are more than 300 kilometers across . The largest . Ceres . was as dwarf planet . At one time , scientists thought that asteroids were the ol shattered planet . the combined mass of all the asteroids is too small In support this idea . Scientists now that the asteroids arc pieces of the early solar that came together to form planet . Sonic asteroids have very elliptical that bring them closer to the sun than Earth orbit . one of these could hit Earth . Ont or mini large asteroids did hit Forth about 65 million ago , with dust and and blocking out sunlight around the world . that many of , ing the dinosaurs . became extinct as a result . Name the tour largest asteroids . 29 Asteroids The asteroid belt ( right ) lies between Mars and Jupiter . Asteroids come in many sizes and shapes . The photo below shows the oddly shaped asteroid Eros .

Meteors It ii night fur ' and . streak ui light flashes the ' rut an or so , see mite minute are shower . Meteor showers happen , NICK , when there is no ' you can we it you Int city lights and the sky not , On ' i ( i ' chunk at rock Ul dust in space . come from comets or asteroids . Sonic ) form when ' collide space . when up and cloud dust that ti mini the solar , Earth through min at these dust . bit at dust ii it enters . tum with the air heat and streak at in si meteor . If the ( it nut ' tum the ( and strike ( tin the tilt mud by . What is a meteorite ?

Section Assessment Target Reading Ski Create rut this section answer the ( Reviewing Key Concepts a . Defining . Listing ' thu ?

Relating Cause and Effect doc ui ( it the ?

hy tin . Describing What is are must Summarizing Him dial the Describing is ' Explaining the ) uid ! and ( entrusting it are the , 30 Meteors make streaks of meteors , like the one above , as they enter the atmosphere . EA . Activity Observing Meteors Meteor showers regularly on dates . The Perseid meteor shower , for example , occurs around August 12 eath year . Look in the newspaper . on the Internet , or in an for information about the next meteor shower . With adult family members , 90 outside on that night and look for meteors . to your family what causes the dismay Chapter 14 515

can , Ol ' Section Integrating Life Science Students know the . general ( relative and size , and motion of iii the solar system . planets . planetary satellites . and asteroids . Students know that living organisms have many kinds ol molecules . including small ones , such as water and salt , and very large ones , as . and DNA . What do living things need to exist on Earth ?

Why do scientists think Mars and Europa are good places to look lor signs at life ?

Key Term I extraterrestrial Is There Life Beyond Earth ?

Yeast Alive or Not ?

Open a package of yeast and pour it unto a bowl . Look at the yeast . Make a list ol your observations . Fill the bowl about halfway with warm water ( about ) Add a spoonful of sugar . Stir the mixture with the spoon . Wait minutes . Now look at the yeast again and make a list of your observations . Think it Over Forming Operational ( ol your observations suggest that yeast is Not alive ?

Which observations suggest that yeast is alive ?

How can you tell it something is alive ?

Most of is covered with snow and ice . You would not expect to set rot ' on top of tho ' But pi ' have found lying on . ice . rocks . they that were . A few of ( ante . Astronomers think that hitting the surface ol ' of fUK ' into span . Sonic ally Earth . In . Cult of that ! front Mars found in has tiny shapes . that look like of ancient life preserved in much . now doubt that thu shapes really any fossils . But if arc , it would ( I sign that similar to bacteria once existed on Mars . Life other than that on Earth would be called extraterrestrial life . 31 Meteorites in Ursula Marvin ( lying down ) studies meteorites like this one in Antarctica .

Life on Earth Sometimes it can be hard to tell whether something is alive or not . But all living things on several ( a in . living things are made up of one or more cells . living things take in energy and use it to grow and develop . They reproduce . producing new living things of the same type . living things also give off waste . The Goldilocks Conditions No one knows whether life exists anywhere other than Earth . Scientists often talk about the needed by life as we know it . Earth has liquid water and a suitable temperature range and atmosphere for living things to survive . Scientists call these able conditions the Goldilocks conditions . That is . the is not too hot and not too cold , It is inst right . were much hotter . water would always be a vapor . Ill Earth were much ( older . water would always be solid ice . Are these the conditions necessary for life ?

Or are they just the conditions that Earth living things happen to need ?

lists have only one example to study life on Earth . Unless scientists lind evidence of life somewhere else , there is no way to answer these questions for certain . Extreme Conditions Recently , scientists have discovered ing things in where it was once believed that life could not exist . Giant tubeworms have been found under the high pressures at the bottom of the ocean . isms have found in the of hot springs Tiny have been discovered deep inside solid rock . Scientists have even found animals that do not require the energy . but instead get their energy from chemicals . These astounding discoveries show that the range of in which life can exist is much greater than scientists once thought . there he in the solar system that do not need the conditions ?

What are some characteristics of all living things ?

31 Hot Spring Bacteria that thrive in water help to the striking colors of Grand Prismatic Spring in Wyoming . How does studying unusual organisms on Earth help scientists predict what extraterrestrial life might be like ?

Communicating You are writing a letter to a friend who lives on another planet . Your friend has never been to Earth and has no idea what the planet is like . Explain in your letter why the conditions on Earth make it an ideal place for living things . 511

For Links on liie Visit Web code noun ! Liquid Water on Mars The patterns on the surface at Mars Indicate that liquid water once flowed there . Applying Concepts Why does this evidence make it more likely that there may once have been life on Mars ?

i Life Elsewhere in the Solar System ?

Recall that Mars is the planet most similar to . That makes Mars the most obvious place to look for living things . Life on Mars ! Spacecraft have found regions on the surface of Mars that look like with crisscrossing paths of water . Shapes like those shown in Figure 33 were almost formed by water . Since life as we know it requires water . hypothesize that Mus may have once had the conditions needed for life to exist . twin Viking spacecraft reached Mars . Each of the Waking landers a small laboratory meant to search for life forms . These laboratories tested ars air and soil for signs of life . None of these tests showed evidence of life . More recently , the Spin and Opportunity rovers found rocks and other surface features on Mars that were certainly formed by liquid water . However . the rovers were not equipped to search for past or present life . Interest in life on Mars was increased by a report in 1996 about a meteorite from Mars that may contain fossils . The scientists report started a huge debate . What were the things in the meteorite ?

Some scientists have suggested that the tiny shapes found in the meteorite am too small to be the remains of life forms . The shapes may have come from natural processes on Mars . The most effective way to answer these questions is to send more probes to Mars . Future Mars missions should be able to bring samples of rocks and soil back to Earth for detailed analysis . Scientists may not yet have evidence of life on Mars . but hope is growing that we can soon learn the truth . What did the Spirit and Opportunity rovers discover on Mars ?

as Martian ! This Electron microscope image shows tiny shapes found in a meteorite from Mars . These structures are less than the width of I human hair .

Life on Europa ?

Many scientists think that . one of moons , may have the conditions necessary for iii to develop . Europa has it . icy crust with giant cracks . up rum thi space prob shun that ice has broken up and . resulting in large twisted blocks of ice occur in the ice crust over . i ( that there is liquid ocean under . The in the ocean could be kept liquid by heat ing from inside . If then is liquid , there might also be life . How could scientists study conditions under ?

future space probe might be able In use radar to see through I ?

icy crust . that . probes could he sent to drill the In for in below . 35 Exploring Scientists have discussed sending a robotic probe to sear ( for life in the below i trust Section Assessment Target Reading Skill , arc oi the main being in this ?

Reviewing Key Concepts INT Cause and Effect doe lift on Earth to ?

I ) Summarizing is Til conditions ! I . Applying ( Do you think there ii ) II ( in ?

Him a . Explaining Why do think there ( be lily on identifying ( think that in the past Mars have . for life to conditions ! they Hill ?

Reading ) Making Generalizations ' I do and Europa share with birth that ' hum tu , life ?

71 Make a Message imagine that scientists have found intelligent extraterrestrial life With family members , make up a message to send to the extraterrestrial Remember that they will not understand English , so you should use symbols and drawings in your message . 14 579

Chapter 14 Study Guide ' The solar system the sun . the planets and their means . and smaller objects such as comets . asteroids . and . Observing the Solar system Key I In gem . is at the center , system , Earth and the other planets revolve around the urn . the . three lam that the til the . The system planets and their . and a series of smaller that around the sun . Key Terms ellipse unit The Sun Key ( in , The sun energy . The , and convection . The til the , and . on or inst above the stink include . and solar Key Terms nuclear convection ' I ' Planets Key Concepts I The inner are and . unique our system in having ( at its . is the terrestrial planet . structure is ' tu . Liquid water the distant petal . Key Terms planets greenhouse 5800 The Outer Planets Key Concepts , and Neptune are much larger and more ' than . do not have solid . I the largest and mint planet in the solar . I Saturn has . and of rotation la tilted at an of about 90 the Neptune is a cold . blue planet . Its contains clouds . I has a solid and denser than the utter . Key Terms I giant I ting Comets . and Meteors Key ( all , and small particles are usually long , narrow . the the and . Key Terms nucleus ( I hell I meteorite Is There Life Beyond Earth ?

Key Concepts , Earth has liquid water and a suitable range and . Mars may nut had the conditions for lift to must . there might also be life . Key Term Review and Assessment Target Reading Skill Create Outlines In your . outline Section I ( tin . I . Earth at the Center Go . For Visit ( Web Code ( observing the Solar system Greek Observations . at the center of revolving planets and stars Ptolemy Model Planets on small circles that move on bigger . Model was incorrect . but a ( for years II . Sun at the Center A . Reviewing Key Terms Choose the letter of the best answer . a an . A . The part sun where nuclear fusion is the . is at a . Inner planet . terrestrial planet . planet . gas giant . The , where ' are found is the a . belt . I ) A that reaches Earth ) iii tunnel . aster old . thought that the solar the following sentences so that your answers clearly explain the key . Each planet around the sun III an is . I . The is the layer um MINT . has the hottest ' of any plant ! of the greenhouse effect , winch is . the other gas giants . I ' 10 . I life , which is , might be found . Writing in Science News Imagine you are on a mission we explore the solar system . write a news report telling the story of your trip from Earth to another terrestrial planet and to a gas giant . include a description of each planet . The Solar system 14 Sill

Review and Assessment Checking Concepts 11 . the ' yi hii and to modern . 12 . What is the ?

13 . Why ( have very ?

14 . Why can see the clearly hut nut the surface nI ' 15 do have that water om nit Mutts ?

Math Practice 16 . Circumference Mars has radius ot ' at Equator . its 17 . Circumference i ( I ( ut about at its . Calculate its radius . Thinking Critically 18 . Applying Concepts is hotter be ifit had no . 19 . Predicting Do you think all at the ni ( planets ?

10 . Comparing and Contrasting ( and comets . uni . 21 . Classifying lurk in the ( Do you think it represents the structure nta terrestrial planet ur a gas giant ?

Gaseous hydrogen and helium Liquid hydrogen and helium Liquid ices Rocky core 5820 12 . Making Generalizations Why ( the discovery of liquid water an another planet he important ?

Applying Skills Use the diagram of an imaginary , newly discovered planetary system around Star to answer Questions . of A , mitt ( lift 75 Earth . 200 days . and 300 Birth days . 40 A Star 23 . Interpreting Data Whi ( planet in this new around Star in the shortest of time ?

24 . Making Models In far will melt have I ( Star ?

the and of the three planets tind out . How tar will each planet hem Star in 100 days ?

Sketch their positions . 25 . Drawing Conclusions ( Lin ( I ever be closer to Planet A than to Planet ?

Study your , this nut . Standards Investigation Performance Assessment your Walt ul ' the solar . Display your data showing how you did the ( and how yuu tut accuracy .

' Standards Practice Choose the letter of the best answer . What characteristic do all of the inner planets A They are larger and more massive than the sun . I They have thick atmospheres of hydrogen and helium . They have rocky surfaces . They each have many . use . Mercury has a daytime temperature of about and a nighttime temperature below , What is best ?

A Mercury has it greenhouse effect . Global warming is occurring on Mercury . Mercury is the closest planet to the sun . Mercury has no real atmosphere . The process by which the sun produces energy is called A combustion . I a chemical reaction . nuclear fusion . nuclear . You can see the planets at night because A they produce their light . I sunlight from their surfaces . nuclear takes place in their cores . their surfaces are brighter than those of the stars . The sun remains stable as I result of a balance between the A outward pressure of nuclear and the inward pull of nuclear fusion . I outward pressure of nuclear fusion and the inward pull of gravity . outward pressure of gravity and the inward pull of nuclear fusion . outward pressure of the effect and the inward pull of gravity . Success ?

Tracker at The table below shows data for five plants In our solar system . Use the table and your knowledge of science to answer . Which planet has a day that is most similar in length to a day on Birth ?

A Mars Uranus Neptune . Light takes about minutes and 20 seconds to travel from the sun to Earth , I AU away . About how long does it take light to travel from the sun In ?

A minutes 25 minutes ( 43 minutes . Which of the following about planets is supported by information in the table ?

A As distance from the sun increases . period of rotation increases . A distance front the sun increases . period of revolution increases . As distance from the sun increases . period of revolution decreases . There is no relationship between distance from the sun and period of revolution . ldea ' three major differences between the terrestrial planets and the gas giants . sea