CHAPTER 27 The Solar System - Weeblyregentsearth.weebly.com/.../4/2/14425382/chapter_27_-_the_solar_sy… · cury of its atmosphere.Impact craters cover the surface of Mercury. Most

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The Solar System

C H A P T E R

27WORDS TO KNOW

asteroid meteor meteoroidcomet meteorite terrestrial planetJovian planet

This chapter will help you answer the following questions:1 Why is Earth so important to us?2 How did the solar system form?3 What do the planets have in common and how is each unique?4 What other objects orbit the sun?

COLONIZING SPACE

The idea of sending people to live away from Earth is a familiarsubject in science fiction. Astronauts have spent extended time inorbit around Earth and have spent several days on the moon. Wemay wish to take advantage of resources, such as precious metals,found on the moon or on other planets.

Living Away from Earth

People living in nonterrestrial, or non-Earthlike, environmentsneed an enormous amount of materials for life support. In a space

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environment near a star, there would be a steady supply of elec-tromagnetic energy. However, things we take for granted, such asoxygen and liquid water, are not available in space. In addition,they are rare on other planets in our solar system. The cost oftransporting these necessities would be huge. Recycling these ma-terials seems more practical.

Beyond the Solar System

In the past few years, astronomers have discovered hundreds ofplanets in orbit around other stars. If other planets like Earth exist,it seems logical that life and civilizations might have developed onsome of them. However, attempts to detect radio signals fromother civilizations in space have failed. Therefore, there is no di-rect evidence that humans could exist anywhere outside Earthwithout complex artificial support systems.

These discoveries have helped us appreciate how unique andhow fragile our environment on Earth is. In spite of fears that aglobal disaster could make Earth uninhabitable, we have nowhereelse to go. Clearly, the best alternative is to preserve our current ter-restrial environment in a way that allows all living things to prosper.

WHAT IS THE ORIGIN OF THE SOLAR SYSTEM?

Evidence from space tells us that originally the universe probablywas nearly all hydrogen and helium. The early universe most likelyhad a large number of very massive stars that used up their hydro-gen fuel relatively quickly. These stars became unstable and ex-ploded, creating clouds of debris full of heavy elements. In oursolar system, there is a large quantity of heavy elements, such ascarbon, iron, silicon, and oxygen. This indicates that our solar sys-tem formed from the remains of a stellar explosion known as a su-pernova. Visit the following Web site to see the relative sizes ofEarth, the other planets, the sun, and our galaxy: http://newsizeofourworld.ytmnd.com

Nebular Contraction

The cloud of debris left over from the supernova explosion mayhave come together under the influence of its own gravity. This

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theory is sometimes called the nebular contraction theory. It sug-gests that the solar system began as a cloud of dust and gas inspace. This cloud is commonly called a nebula. More than 99 per-cent of the mass condensed to form the sun, which is at the cen-ter of our solar system. Debris that remained formed the planets,dwarf planets, moons, and other objects orbiting the sun.

Just as an ice-skater spins faster when she brings in her arms,the collapse of this material produced the revolution of the plan-ets in their orbits. It also caused the rotational motion of the sunand planets. All the planets revolve in the same direction that thesun rotates. Most of their moons also revolve in this direction. Thespacing of the planets is remarkably ordered. Most planets areabout twice as far from the sun as is their neighbor closer to thesun. In addition, the planets lie in nearly the same plane, orbitingthe sun in a thin disk. This degree of order suggests that a singleevent formed the solar system.

Scientists have studied radioactive elements within materialthat has fallen to Earth and rocks recovered from the older partsof the moon. They estimate that these bodies are about 4.6 billionyears old. Rocks from Earth are not as helpful because they havebeen recycled through the rock cycle and plate tectonics. There-fore, the oldest known terrestrial rocks are less than 4.6 billionyears old. The patterns of change in stars indicate that the sun isabout 5 billion years old. It therefore seems likely that the sun andthe solar system formed in a single event that took place a littleless than 5 billion years ago. This is only about one-third of theestimated age of the universe.

WHAT PROPERTIES DO THE PLANETS SHARE?

The definition of a planet has evolved. Early observers of the nightskies thought of the planets as special stars that wander among theother stars. Later, astronomers using telescopes were able to seedifferences between planets and stars. They began to think ofplanets as large objects that orbit the sun, reflecting the sun’s light.

Like all satellites, the planets orbit the sun in ellipses with theprimary, the sun, located at one focus. Their orbits have low eccen-tricities.The change in gravitational force between a planet and thesun causes the orbital velocity of the planet to change in a yearly

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CHAPTER 27: THE SOLAR SYSTEM ! 663

cycle.All the planets move a little faster when they are closest to thesun because that is when the gravitational attraction of the sun isgreatest. Visit the following Web site to use the Solar SystemViewer, which shows motions of the planets with stop action andspeed controls: http://janus.astro.umd.edu/javadir/orbits/ssv.html

Each planet in the solar system moves along its orbit at its ownspeed.As distance from the sun increases, the pull of the sun’s grav-ity decreases. Therefore, orbital velocity is indirectly related to aplanet’s distance from the sun.That is, the farther the planet is fromthe sun, the slower it travels in its orbit.The innermost planet, Mer-cury, moves nearly 10 times as fast along its orbit as the outermostplanet, Neptune. Mercury, because it is closer to the sun, also has ashorter orbit than any other planet. Therefore, Mercury revolvesaround the sun in only 88 Earth-days. Earth takes 1 year. Neptunetakes nearly 165 Earth-years to revolve around the sun. The differ-ence in orbital period is so large because of the combined effects ofthe longer orbits and the slower speeds of the outer planets.

All planets rotate on their axis. However, unlike the orbital prop-erties of the planets, their rotation does not follow a regular pat-tern. Neither their size nor their distance from the sun is relateddirectly to their period of rotation. The largest planet, Jupiter, takesonly about 10 Earth-hours to rotate 360°. Therefore, the length ofa day on Jupiter is 10 Earth-hours. Venus has the longest period ofrotation, about 8 Earth-months. Furthermore, two of the planets(Venus and Uranus) do not rotate in the same direction as theother planets. Perhaps the rotation of these planets was affected bycollisions with other objects after the solar system formed nearly 5billion years ago.

The number of moons orbiting the planets shows a generalpattern with distance from the sun. The two innermost planets,Mercury and Venus, have no moons. Earth has one moon. Thenthe number of moons generally increases as we move to the outerplanets. However, the number of moons changes as more are dis-covered. It is difficult to distinguish between moons and other ob-jects that orbit the outer planets. The question of how small anobject can be and still be called a moon has no clear answer. Forexample, the rings of Saturn and less visible rings of other gas gi-ants are made of millions of objects that orbit the planet in thesame plane, but these objects are considered too small to be calledmoons. At this time, there is no known limit to the number of


moons in the solar system. Figure 27-1 shows properties of themembers of our solar system. (Note: Time is expressed in units ofEarth-time. Thus, “days” are approximately 24 Earth-hours long.)

STUDENT ACTIVITY 27-1 —GRAPHING SOLAR SYSTEM DATA

Your teacher will divide the class into groups and give each groupa piece of graph paper. On the piece of graph paper, write “Sun”

followed by the names of the eight planets equally spaced along thehorizontal axis. The vertical axis can be any one of the eight vari-ables listed in Figure 27-1. Each group should make a graph dis-playing different data. Your teacher may share the graphs to theclass. What relationship does each graph show between the positionof the planets and the characteristic graphed?

HOW ARE THE PLANETS GROUPED?

Astronomers divide the planets into two groups. The four planetsclosest to the sun are the terrestrial planets because they are sim-ilar to Earth in their rocky composition. The four outer planets are

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FIGURE 27-1. Solar System Data.

called the Jovian planets because they are similar to Jupiter.Jupiter is a large planet that has a relatively low density. Most ofJupiter’s volume is a thick shell of gas. Figure 27-2 compares thesize of the sun and the planets.

Terrestrial Planets

Mercury, Venus, Earth, and Mars are the closest planets to thesun. These four planets are solid objects surrounded by a relativelythin atmosphere or no atmosphere at all. Mars, with the largestorbit in the group, is less than one-third of the distance to the nextplanet, Jupiter.

MERCURY The closest planet to the sun, Mercury, is a smallplanet. It therefore has weaker gravity than most of the other plan-ets and it does not have a magnetic field. Electromagnetic radiationand charged particles from the sun (solar wind) have stripped Mer-cury of its atmosphere. Impact craters cover the surface of Mercury.Most craters probably formed from collisions with debris early inthe history of the solar system. At that time there was more debrisscattered through the solar system. With no atmosphere and no


FIGURE 27-2. This diagram shows the sizes of the planets and dwarf planetsto scale, but their distances from the sun are not to scale. (If distance and sizewere to the same scale, most planets would be too small to see.) The newcategory of dwarf planets will be discussed in page 672.

weather, these features are still evident after billions of years. Theslow rotation of Mercury and the lack of an atmosphere cause anextreme range in temperature on the surface. Temperatures rangefrom 400°C during the day to !200°C at night. Because it is rela-tively close to the sun, Mercury is visible from Earth only nearsunset or sunrise. Visit the following Web site to see the currentposition of the planets in our solar system by selecting your timeand your location: http://www.fourmilab.ch/cgi-bin/Solar

VENUS Like Mercury, Venus is closer to the sun than is Earth;therefore, Venus is visible from Earth only near sunset or sunrise.Venus is sometimes called Earth’s twin because its diameter andmass are similar to Earth’s. Venus therefore has about the samegravity as Earth. For many years, astronomers wondered if Venusmight have surface conditions similar to those on Earth. Thickclouds prevented direct observations of the solid surface. Radarimages and mapping by artificial satellites revealed that Venus hasvolcanic features like Earth.

The surface conditions on Venus are very different from Earth’s.Atmospheric pressure at the surface is 90 times the sea-level pres-sure on Earth. The thick atmosphere of Venus is mostly carbondioxide, which traps solar energy (the greenhouse effect). There-fore, the surface temperature of Venus (about 500°C) is actuallyhotter than the daytime temperature on Mercury. In addition,the clouds of Venus are composed of droplets of highly corrosivesulfuric acid.This would be deadly to the kind of creatures that liveon Earth.

Venus takes longer to rotate than any other planet. In fact,Venus takes longer to rotate on its axis than it takes to revolvearound the sun. (See Figure 27-1 on page 665.) So much for our“twin planet.”

PHASES OF MERCURY AND VENUS As viewed from Earth, theportion of the lighted surface of Mercury and Venus changes in apredictable cycle. Like the moon, these two planets show a fullrange of phases. Galileo was the first astronomer to document thephases of Venus as he observed them with his telescopes.

When Mercury and Venus pass between Earth and the sun,they, like the new moon, appear dark as viewed from Earth. This isillustrated in Figure 27-3, on page 668.Then, the lighted portion of


each planet increases until it is fully lighted as the planets pass be-hind the sun. This change in phase is accompanied by a change inapparent size. Mercury and Venus appear largest at their closestapproach to Earth in the crescent phase.As they move farther fromEarth and the lighted portion increases, these planets appearsmaller in angular diameter. The orbits of the other planets areoutside Earth’s orbit. The night side of Earth faces the lighted sideof these planets. Therefore, they never show the dark, or new,phase. They always appear mostly lighted as observed from Earth.

EARTH Oceans cover about 70 percent of Earth’s surface. Theyaverage about 4 km (2.5 mi) in depth. In fact, Earth is the onlyplanet scientists know to have large amounts of water in all threestates: ice, liquid water, and water vapor. Surface temperatures aremoderate from a record low of !89°C (!128°F) in Antarctica to58°C (136°F) in Africa’s Sahara Desert.

Earth’s unique surface conditions have supported the evolutionof many forms of life. In addition, living things changed the planet.


FIGURE 27-3. The thick clouds that cover Venus make it appear featureless invisible light. Depending upon the positions of the sun, Earth, and Venus, theapparent size and lighted part of Venus (the phase) change.

Earth’s original atmosphere probably was mostly carbon dioxidelike that of Venus. The carbon dioxide content of the atmosphereis now less than 1 percent (0.03 percent). Most of the original car-bon of the atmosphere has dissolved in the ocean or become partof plants, animals, or rocks. Weathering and erosion along withplate tectonics constantly change Earth’s surface.

MARS Ancient astronomers named Mars after the Roman godof war because of its red color. Of the eight planets in our solarsystem, the conditions on Mars come closest to the favorable con-ditions for life found on Earth. Like Venus, the atmosphere ofMars is mostly carbon dioxide. However, the atmosphere of Marsis much thinner than that of Venus or Earth. Mars can warm upto a comfortable 20°C (68°F) near the Martian equator. However,at night, about 12 h later, it cools to !60°C (!76°F) because thethin atmosphere does not absorb and radiate heat. Due to the tiltof the rotational axis of Mars, it has seasons like Earth. However,the polar regions become so cold that solid carbon dioxide (dryice) forms on the surface. Landing modules sent to Mars havetransmitted photographs and other data from its red surface.

Some Martian surface features look as if they were formed bylarge rivers. However, there is no liquid water on the surface ofMars today. This has led some astronomers to theorize that mostof the atmosphere of Mars has been lost and that the climate onMars was warmer in the past. If the water is still there, it is prob-ably in the form of ice under the planet’s surface. All forms of lifeon Earth need water. So scientists theorize that primitive life formsmay exist below the Martian surface.

STUDENT ACTIVITY 27-2 —DESIGN A LANDING MODULE

NASA has hired your group to design an instrument module thatwill send back information about Mars after it reaches the

planet. Your module may include only easily obtainable instrumentsthat you can understand and operate. Make a drawing of the moduleand write an explanation of what each instrument is as well as whatinformation it will gather. Radio communication will be your onlylink. NASA is not sending people or animals to Mars on this mission.

1: ENGINEERINGDESIGN 1


The Outer Planets

The outer planets are Jupiter, Saturn, Uranus, and Neptune. TheseJovian planets are larger and less dense than the terrestrial plan-ets. They are composed mostly of hydrogen and helium ratherthan the heavier elements (iron, silicon, and oxygen) of the ter-restrial planets. The Jovian planets have small, rocky cores sur-rounded by a liquid mantle and a thick gaseous shell. However,they are still the most massive planets because of their huge size.Each Jovian planet also has a system of rings around it. Theserings are made of small particles that orbit independently in theplane of the planet’s equator.

JUPITER The first of the outer planets, Jupiter is the largestplanet in the solar system. Jupiter alone makes up two-thirds ofthe total mass of the eight planets. Jupiter is more than 99 percenthydrogen and helium. This is more like the composition of a starthan the composition of the terrestrial planets. The pressure at thecenter of Jupiter is about 10 times the pressure within Earth.However, it is still not enough pressure to support nuclear fusion,which powers the sun and other stars.

Jupiter’s rapid rotation causes a noticeable bulge at its equator.One of Jupiter’s other noticeable features is the Great Red Spot.Some astronomers think that this may be a permanent, ragingstorm. Others think it is an area of calm within the turbulent at-mosphere. With binoculars or a small telescope, you can see fourof Jupiter’s many moons from Earth. They sometimes look like aline of stars that runs through the equator of Jupiter. These foursatellites are known as the Galilean moons, named after their dis-coverer, Galileo.

SATURN The rings of Saturn make it one of the most unusualobjects in the night sky. Saturn’s rings are made of ice particles anddust. They might have become a moon if this debris were not soclose to Saturn and broken by Saturn’s gravitational field. Theserings are sometimes visible through binoculars from Earth, as inFigure 27-4. Rings of the other Jovian planets are less dense andtherefore more difficult to see. Second in size only to Jupiter, Sat-urn is also composed primarily of hydrogen and helium. It is theleast dense planet with an average density less than that of water.


URANUS AND NEPTUNE Uranus and Neptune are almost alike.They are composed mostly of gas. Although less than half the di-ameters of Jupiter and Saturn, they are much larger than Earth.Uranus and Neptune are not as bright as the other planets. There-fore, they were not discovered until telescopes were turned to theheavens about the time of Galileo. Uranus, the brighter of the two,is barely visible without binoculars or a telescope.They are dim be-cause they are so far from the sun. In addition, they are not as largeas Jupiter and Saturn. The rotational axis of Uranus is tilted nearly90°, so it seems to spin on its side. Neptune is very similar in sizeand composition to Uranus, but nearly twice as far from the sun.

As the most distant planets, Neptune and Uranus are the cold-est planets. At the cloud tops, which we see as the outer part ofthese planets, both have temperatures below !220°C.

STUDENT ACTIVITY 27-3 —THE SOLAR SYSTEM TO SCALE

Use the data in the Earth Science Reference Tables to construct ascale model of the solar system. If you use a single scale for the

size of the planets and their distance from the sun, you will proba-bly need to work outside. For smallest planets to be dots on a sheetof paper, the distance to Neptune may need to be greater than thesize of your school building.

WHAT OTHER OBJECTS ORBIT THE SUN?

From its discovery in 1930 until 2006, Pluto was the ninth planet.However, in many ways it is different from the outer planets. For along time, Pluto had puzzled astronomers because it is so different

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FIGURE 27-4. Saturn’s ringsare composed of particles ofrock and ice. There are sevengaps in the rings, created wheremoons have swept up debriswith their weak gravitationalattraction. In this view Saturn iseclipsing the sun.


from the four outer planets. Unlike these gas giants, Pluto is smalland relatively dense. Pluto has a more eccentric orbit than any ofthe planets. In fact, Pluto is sometimes closer to the sun than isNeptune.

Recently, astronomers have discovered many objects in theouter solar system that are similar to Pluto. In 2003, they discov-ered Eris, which is 27 percent more massive than Pluto and far-ther from the sun.

Dwarf Planets

In 2006, the IAU (International Astronomical Union) defined theterm planet for the first time. This definition left out Pluto. TheIAU created a new group of solar system objects: the dwarf plan-ets. The IAU classified Ceres, Eris, and Pluto as dwarf planets.Ceres is in the asteroid belt between Mars and Jupiter. Its radiusis about 10 percent of Earth’s. Pluto and Eris have larger orbitsthan any of the planets. The radius of each is about 20 percentof Earth’s. Makemake was added in 2008. All four are nearly asdense as rocks found near Earth’s surface. Ceres, Pluto, Make-make, and Eris are shown in proper order in Figure 27-2 on page666. With better telescopes and technology, astronomers are dis-covering more dwarf planets.

Asteroids

The asteroid belt is a ring of debris that separates the terrestrialand Jovian planets. Asteroids are irregularly shaped rocky ob-jects that are smaller than planets. They orbit the sun in the samedirection as the planets. Perhaps the asteroids are debris left overfrom the formation of the solar system. Earth’s gravity has pulledsome asteroids to its surface. Evidence from these asteroids indi-cates that they may be the remains of a planet that broke intomany fragments when it was struck by another object. The spac-ing between Mars and Jupiter is larger than the pattern observedamong other planets. This supports the idea of a missing planet.Visit the following Web site to take the Asteroid Challenge:Target Earth, a virtual lab where you will learn about the near-Earth asteroid, Apophis: http://spaceclass.org/apophis/. Visit the


following Web site to answer the question: Did an asteroid causea tsunami in New York 2300 years ago (with animation)? http://dsc.discovery.com/news/2008/11/20/asteroid-tsunami-print.html

Comets

Occasionally, we can see comets in the night sky. They appearas a small spot of light with a long tail that points away from thesun. (See Figure 27-5.) Comets have highly eccentric orbits. Thismeans that they spend the great majority of their time in the farouter reaches of the solar system. Many comets orbit the sun be-yond the orbit of Neptune. Some comets seen in the inner solarsystem were probably pulled into highly elliptical orbits aroundthe sun by the gravity of a passing star or other object in space.When comets enter the inner part of the solar system near Earthand the sun, they move quickly under the influence of the sun’sstrong gravitational field. The brightest comets are usually visi-ble for several weeks. Then, they return to the outer portion oftheir orbits.

Comets are sometimes called dirty snowballs because they aremade of ice and rock fragments. When comets come close to thesun, some of the ice and dust escapes. These particles form thecomets’ distinctive tails. Only about 30 comets per century arebright enough to be seen without a telescope. The best known isHalley’s (HAL-ease) comet. It returns to the inner solar systemabout every 75 years, and it usually is visible without a telescope.Halley’s Comet was visible in 1986, and will return in 2061.

FIGURE 27-5. Comets are icy objectswith highly eccentric orbits. Cometsform visible tails as they pass throughthe inner parts of the solar system.Most comets are very dim. They donot streak quickly through the sky likemeteorites. They can remain visible inthe same part of the sky for weeks.


Meteors

On a clear night, it is sometimes possible to see streaks of lightthat move across a portion of the sky, usually in a fraction of a sec-ond. These are solid bits of rock from outer space that enter theupper atmosphere at great speed. Friction with the atmospherecreates a streak of light known as a meteor. Table 27-1 lists thetimes of the year when meteors are especially numerous. Visit thefollowing Web site to watch a large meteor as it streaks across the

Table 27-1 Meteor Showers

Duration Number per Date of Above 25% Approximate Hour at

Name/Source Maximum of Maximum Limits Maximum

Quadrantids Jan. 4 1 day Jan. 1–6 120

Aquarids July 27–28 7 days July 15–Aug. 15 35

Perseids Aug. 12 5 days July 25–Aug. 18 90

Orionids Oct. 21 2 days Oct. 16–26 30

Geminids Dec. 14 3 days Dec. 7–15 120

FIGURE 27-6. Aerial and ground-level views of Meteor Crater, Arizona. Knownas the world’s most spectacular impact structure, Meteor Crater is 1 km (0.7mi) wide and 170 m (570 ft) deep. The white arrow shows where the ground-level photograph on the right was taken. For scale, note the spectatorslooking down into the crater from the platform at the lower right.

sky in Canada: http://www.youtube.com/watch?v"Os9FrsVMZew&feature"related

As they move through space, the bits of rock are called mete-oroids. Most meteoroids burn up before they reach the ground.However, the larger ones often survive their fiery trip through theatmosphere. Those that strike Earth’s surface are called mete-orites. Meteorite impacts have left many craters. One is Arizona’sfamous Meteor Crater (Barringer Crater), seen in Figure 27-6. Sci-entists study meteorites to learn about the origin of the Earth andsolar system. Nearly all meteorites are debris left over from theformation of the solar system.

Astronomers divide meteorites into two groups. The most com-mon are the stony meteorites. They are composed of mineralscommon in Earth’s mantle layer. Other meteorites are mostly iron.They are thought to be similar to the composition of Earth’s core.Figure 27-7 shows an iron meteorite. Visit the following Web siteto learn more about the Willamette Meteorite: http://www.amnh.org/rose/meteorite.html


FIGURE 27-7. The WillametteMeteorite was found in Oregonand acquired by the AmericanMuseum of Natural History in1906. It is an iron meteoriteweighing over 15.5 tons, the sixth largest meteorite inthe world. The holes werecaused by millions of years ofweathering in the wet Oregonclimate.


CHAPTER REVIEW QUESTIONS

Part A

1. Which planet is approximately 10 times farther from the Sun than is Earth?

(1) Mars (3) Saturn(2) Jupiter (4) Uranus

2. Which object has the greatest density?

(1) Earth (3) Jupiter(2) the moon (4) the sun

3. What is the approximate inferred age of our solar system?

(1) 1.3 billion years (3) 14 billion years(2) 4.6 billion years (4) 149 billion years

4. Which bar graph below correctly shows the orbital eccentricity of the eight plan-ets of our solar system?

5. Which object is closest to Earth?

(1) the sun (3) Venus(2) the moon (4) Mars


6. Large craters found on Earth support the hypothesis that impact events havecaused

(1) a decrease in the number of earthquakes and an increase in sea level(2) an increase in solar radiation and a decrease in Earth radiation(3) the red shift of light from the most distant stars in the universe(4) mass extinctions of life-forms and global climate changes

Part B

Base your answers to questions 7 and 8 on the diagram below, which shows the inferred sequence of changes by which our solar system formed from spacedebris.

7. How did the young sun form between stages B and C?

(1) Gravity caused the center of the cloud to contract.(2) Gravity caused heavy dust particles to split apart.(3) Outgassing occurred sending jets of material outward.(4) Outgassing from Earth provided material to make the sun.


8. After the young sun formed, the disk of gas and dust

(1) became a large sphere(2) split into two massive objects(3) became larger in diameter(4) formed into the planets

Base your answers to questions 9 through 11 on the passage below and yourknowledge of Earth science.

A Newly Discovered Planet

Scientist studying a sun-like star named Ogle-Tr-3 discovered a planet that is,on average, 3.5 million km from the surface of the star. The planet was discov-ered as a result of observing a cyclic decrease in the brightness of Ogle-Tr-3every 28.5 h. The changing brightness is a result of the planet blocking someof the starlight when it passes between the star and Earth. This observationenabled astronomers not only to find the planet, but also to determine its massand density. The mass has been calculated to be approximately 159 times themass of Earth. The new planet is only 20 percent as dense as Jupiter. Scientiststhink that the low density is a result of the planet being very close to the starOgle-Tr-3.

9. Compared to the periods of revolution of Mercury and Venus, the newly discov-ered planet’s period of revolution is

(1) shorter than both Mercury’s and Venus’s(2) longer than both Mercury’s and Venus’s(3) shorter than Mercury’s but longer than Venus’s(4) longer than Mercury’s, but shorter than Venus’s

10. The density of this newly discovered planet is approximately

(1) 0.1 g/cm3 (3) 1.3 g/cm3

(2) 0.3 g/cm3 (4) 2.0 g/cm3

11. Which similar light-decreasing event in our solar system is the result of themoon being between Earth and the sun?

(1) summer solstice(2) winter solstice(3) solar eclipse(4) lunar eclipse


Part C

Base your answers to questions 12 through 15 on the diagram below, which showsthe orbits of the four inner planets of our solar system. The dot on each orbitshows where the planet is closest Sun.

12. Make a copy or sketch of the diagram above and write a W on the orbit of Marswhere the gravitation attraction between the sun and Mars is weakest.

13. Circle the name of the largest of the four inner planets.

14. How long does it take Mercury to spin once on its axis?

15. What is the precise shape of these planetary orbits and the shape of all orbits ofsatellites around their primaries?

Base your answers to questions 16 through 18, on page 680, on the diagram below,which shows the inferred interiors of the four terrestrial planets.

16. What are the two most common elements in the crusts of Mercury, Venus, Earth,and Mars?

17. Which two planets would allow S-wave earthquake waves to pass through thecore to the opposite side of the planet?

18. How are the densities of the terrestrial planets different from the densities of theJovian planets?

Base your answers to questions 19 and 20 on the graphic below, which shows therelationship between the distance of a planet from the sun and the temperature offormation. (1 AU is Earth’s distance from the sun.) The shaded zones indicateplanetary composition when it first formed.

19. According to this graph, what was the composition of Neptune at the time of itsformation?

20. What is the relationship between the distance of a planet from the sun and thetemperature when it became a planet?


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CHAPTER 27 The Solar System - Weeblyregentsearth.weebly.com/.../4/2/14425382/chapter_27_-_the_solar_sy… · cury of its atmosphere.Impact craters cover the surface of Mercury. Most