WIXLIB

4Viking Orbiter 1 took images of Mars in 1980 that were used tocompose this false-color mosaic.The U.S. Geological Survey produced this color-enhanced imageof Jupiter from a Voyager 1 image captured in 1979.MarsJupiterMars—the fourth planet, the Red Planet—has polarice caps and markings that looked, through 19thcentury telescopes, to be similar to human-madewater canals on Earth. American and Russian orbitersdid not disclose any canals on Mars, but they did findevidence of surface erosion and dried riverbeds, indicating the planet was once capable of sustaining liquidwater. For millions of years, the Martian surface hasbeen barren of water; Mars is too cool and its atmosphere is too thin to allow liquid water to exist. There isno evidence of civilizations, and it is unlikely that thereare any extant life forms, but there may be fossils of lifeforms from a time when the climate was warmer andliquid water existed.Jupiter, the fifth planet, is the largest, containing two-thirdsof the planetary mass of our solar system. Jupiter is like asmall sun with its own miniature solar system; it is composed of hydrogen and helium and has 16 moons, as wellas a thin, three-band ring system. Jupiter does not burn likethe Sun because it contains only one-eightieth of the massneeded to ignite its liquefied gas.Mars is a small rocky planet. The surface of Mars retainsa record of its evolution, including volcanism, impactevents, and atmospheric effects. Layered terrains nearthe Martian poles suggest that the planet’s climate changeshave been periodic, perhaps caused by a regular changein the planet’s orbit. The crust of the planet seems to movevertically, with hot lava pushing upwards through the crustto the surface. Periodically, great dust storms occur thatengulf the entire planet. The effects of these storms aredramatic, including dunes, wind streaks, and wind-carvedfeatures.Mars has some remarkable geological characteristics,including: the largest volcanic mountain, OlympusMons (27 km high and 600 km across), in the solarsystem; volcanoes in the northern Tharsis region thatare so huge they deformed the planet’s sphericalshape; a gigantic equatorial rift valley, the VallisMarineris; and a “crusted dichotomy,” with the northernthird being young lowlands and the southern two-thirdsancient highlands. This canyon system could easily fitthe Grand Canyon inside it; its distance is equivalent tothat between New York and Los Angeles.Jupiter’s atmosphere contains turbulent cloud layers ofammonia ice, ammonium-hydrogen sulfide crystals, andwater ice or perhaps liquid water.The pressure of Jupiter’satmosphere is strong enough to form a layer of liquidmetallic hydrogen capable of conducting huge electricalcurrents. The persistent radio noise and strong magneticfield of Jupiter could emanate from this layer of metallicliquid. Jupiter’s magnetic field is immense, pouring billionsof watts into Earth’s own magnetic field every day. Theatmosphere bristles with lightning and swirls with hugestorm systems like the Great Red Spot, which havepersisted for at least 100 years (perhaps 400 years).In December 1995, NASA’s Galileo spacecraft arrived atJupiter and deployed a probe into the Jovian atmosphere.The probe fell for nearly an hour, revealing that theatmosphere is much drier than expected and does notexhibit the three-tiered cloud layers anticipated. Further,the atmosphere contained only one-half the expectedhelium. The probe also revealed previously unknownradiation belts and a virtual absence of lightning. Afterreleasing the probe, Galileo embarked on a tour of theJovian system, performing flybys of the largest moons fromas much as 1,000 times closer than did the Voyagermissions. It has recorded volcanic activity on Io andrevealed that the moon has an iron core almost one-half itsdiameter. Also,the moon Europa may have a layerof warmice or liquid water beneath its cracked icy surface. Suchobservations promise to advance our understanding ofsmall bodies of the outer solar system for decades to come.

5Voyager 2 took images of Saturn in 1981, from which this truecolor image of the planet was assembled.Voyager 2 took this image of Uranus in 1986.SaturnUranusSaturn, the sixth planet, is a giant, gaseous planetwith an intriguing atmosphere. Alternate jet streamsof east-west and west-east circulation can be tracedin the motions of the cloud tops; the speeds of thesejet streams reach as much as 625 km/hr and areresponsible for the banded appearance of the clouds.The atmosphere consists mostly of hydrogen andhelium, but also includes trace amounts of otherelements. Electrical processes and heat from internal planetary sources enrich the layered chemicalmix of the atmosphere, which probably transitionsfrom superheated water near the core to the ammonia ice clouds that are observed at the cloudtop. Theplanet’s atmosphere also features storm structuressimilar to Jupiter’s Great Red Spot. Saturn’s magnetic field is 1,000 times stronger than Earth’s.First thought to be a comet, Uranus is the seventhplanet from the Sun. Four times the size of Earth,Uranus’ orbit extends 19 times farther from the Sunthan Earth’s orbit. Tipped, Uranus behaves as agiant top as it spins on an axis almost in the plane oforbit. This motion leads to extreme seasonal variation in what sunlight is available. Over the period ofone Uranian year (84 Earth years), the polar regionsof the planet go through four seasons, as on Earth,with perpetual sunlight in the summer and totaldarkness in the winter. Periods of alternating dayand night are interspersed in the spring and fall. Dueto its great distance from the Sun, Uranus’ temperatures remain a somewhat constant –220 C throughout the year.While Jupiter, Uranus, and Neptune also have ringsystems, Saturn’s ring system is the most extensiveand brilliant. Today we know Saturn has seven majorring divisions. The rings may be the remnants ofmoons destroyed by tidal interaction with Saturn’sgravity. They may include remnants of comets thatpassed too close to Saturn and were likewise destroyed. Rings are composed mostly of ice crystals,ranging in size from a few centimeters to a few meters.The major rings contain hundreds of ringlets, withsome rings being “braided,” others being flanked withsmall moons, and shadowy “spokes” developing anddissipating in the rings.Of Saturn’s 18 moons (two and possible four new moonswere discovered by the Hubble Space Telescope in1995), some are covered in very smooth ice. Saturn’slargest moon, Titan, is a little bigger than Mercury and hasa thick atmosphere of nitrogen. This nitrogen atmospheremay be similar to primordial Earth, perhaps containing thechemical building blocks of life.Uranus’ atmosphere consists primarily of hydrogenand helium, with a small amount of methane andtrace amounts of other gases present. The planet’sbluish-green color is a result of the methane in theatmosphere absorbing red light. The planet’s atmosphere is almost featureless, with faint cloudmarkings between 20 and 50 south latitude. Windspeeds range from 100 to 600 km/hr and blowwestward. At the equator, winds were clocked at1,042 km/hr, over four times faster than the strongest winds on Earth. Uranus has a magnetic fieldsimilar in strength to Earth’s, but the magnetic fieldis tipped by about 50 degrees with respect to the axisof rotation.Uranus possesses a system of at least 11 thin, widelyseparated rings. The rings of Uranus are optically dark,on the average reflecting only 2 percent of the sunlightthat falls on them. Its 15 moons all lie along the planet’sequatorial plane, tipped 98 degrees relative to theplanet’s orbit to the Sun.

6Voyager 2 took this image of Neptune in 1989. The image wasprocessed to enhance the features of the planet.The Hubble Space Telescope’s Faint Object Camera took thisimage of Pluto and Charon in 1994.NeptunePlutoNeptune is the eighth planet and the smallest of thegiant gas planets. Its magnetic field—like that ofUranus—is a highly tilted 47 degrees from the axisof rotation.Pluto is the smallest, coldest, and farthest planetfrom the Sun, with an orbit that is the most ellipticaland tilted. Due to its great distance, Pluto has notbeen visited by spacecraft. As a result, we do notknow much about Pluto.Neptune receives only 3 percent as much sunlight asJupiter; yet it is a dynamic planet and surprisinglyshows several large, dark spots. The largest spot,dubbed the Great Dark Spot, was about the size ofEarth and was similar to Jupiter’s Great Red Spot,which is a hurricane-like storm. Hubble Space Telescope images reveal that the Great Dark Spot isgone. Neptune has the strongest winds on anyplanet, with winds blowing up to 2,000 km/hr. Most ofits winds blow westward, opposite to the rotation ofthe planet. A small irregularly shaped, eastwardmoving cloud “scoots” around Neptune every16 hours or so; this “scooter” could be a cloud plumerising above a deeper cloud deck.Neptune has four rings and eight moons. The ringsappear to be “ring arcs,” or partial rings; however, theyactually are complete. The rings vary in thickness sothat they cannot be fully viewed from Earth. All eightmoons are small and remain close to Neptune’s equatorial plane. Triton, the largest satellite of Neptune, isone of the most interesting satellites in the solarsystem. It shows evidence of a remarkable geologichistory, with active geyser-like eruptions spewing invisible nitrogen gas and dark dust particles severalkilometers into the tenuous atmosphere. Triton’s relatively high density and retrograde orbit offer strongevidence that it is not an original member of Neptune’sfamily, but is a captured object.We do know that Pluto is very small—smaller thanEarth’s moon, some 2,330 km across. The planet’ssurface is slightly reddish, composed of exotic snowsof methane, nitrogen, and carbon monoxide. Plutohas polar caps as well as large, dark spots near theequator. Evidence indicates the existence of a rockand water ice interior. Above the surface lies anatmosphere one millionth the density of Earth’s.Although the atmosphere is much more tenuousthan Earth’s, Pluto’s low gravity (about 6 percent ofEarth’s) causes the atmosphere to be much moreextended in altitude than Earth’s. Because Pluto’sorbit is so elliptical, the planet grows much colderduring the part of each orbit when it is far from theSun. As a result, Pluto’s atmosphere is thought topersist only for the part of its orbit when Pluto is closerto the Sun, as it is now. When it is further from theSun, the atmosphere freezes out on the surface as ice.The moon Charon, which is almost half the size ofPluto, orbits the planet every 6.4 days, at an altitudeof about 18,300 km. Given the rough similarity ofPluto’s size to Charon’s, most planetary scientistsrefer to Pluto-Charon as a double, or binary, planet.Charon’s surface differs from Pluto’s; it is coveredwith dirty water ice and does not reflect as much lightas Pluto’s surface. Charon’s surface is devoid ofstrong color. To date, scientists have not foundevidence to indicate that Charon has an atmosphere.

7This mosaic of asteroid 243 Ida was acquired by Galileo in 1993at ranges of 3,057 to 3,821 km.Taken at Mauna Kea Observatory on Illa-Jemulson in 1986, thisimage of Halley’s Comet stretches over 6 of the sky.AsteroidsCometsA large number of rocky and metallic objects orbitaround the Sun but are too small to be consideredfull-fledged planets. These objects are known asasteroids or minor planets. Asteroids are materialleft over from the formation of the solar system.Some 4,000 numbered and named asteroids circlethe Sun between the orbits of Mars and Jupiter.Scientists speculate that an additional 100,000asteroids exist with diameters greater than 1 km.Most comets reside in the Oort cloud, some 50 to100,000 AU in diameter around the Sun. Cometnuclei orbit in this frozen abyss until they aregravitationally perturbed into new orbits that carrythem close to the Sun. Many of the nearly 900recorded comets have orbital periods in excess of200 years. Some comets pass through the solarsystem only once, while others have their orbitsgravitationally modified by a close encounter withone of the giant outer planets. These latter visitorscan enter closed elliptical orbits and repeatedlyreturn to the inner solar system.The asteroid belt appears to be divided into twovery different regions. The inner asteroid belt(inside about 400 million km) is dominated bymaterials produced by strong heating and meltingof the original proto-asteroids; later fragmentationhas exposed their deep interiors. Beyond 400million km, the belt is dominated by dark objectsrich in carbon, organic molecules, and sometimeswater-rich clay minerals. These materials couldnot have survived significant heating, and asteroids in this region probably preserve much information about the formation of the solar system.A few asteroids in the inner portion of the asteroidbelt are referred to as Mars-crossing or Amorasteroids, because the orbits of these objectscross that of Mars. In addition, well over 30 objectshave been located that come in far enough tocross Earth’s orbit. These Earth-crossing or Apolloasteroids usually measure a few km in diameter,or less, with the largest measuring about 8 kmacross. Most Earth-crossing asteroids appear tooriginate in the main asteroid belt. There is evidence that Earth has been hit by asteroids in thepast. One of the least eroded, best preservedexamples is the Barringer Meteor Crater nearWinslow, Arizona.The nucleus of a comet is an irregularly shaped,almost black aggregate of water ice, carbon, silicone, methane, and ammonia. The average size ofthe nucleus ranges from 1 to 10 km in diameter. Asa nucleus falls inside the orbits of the outer planets,the volatile elements of which it is made graduallywarm. By the time the nucleus enters the region ofthe inner planets, these volatile elements are boiling,forming a coma, or cloud-like “head,” that can measure tens of thousands of km across. The comagrows as the comet gets closer to the Sun.The charged particles from the Sun, known as thesolar wind, push on the coma, blowing it back andforming “tails.” One tail, consisting of of gases andions, is pushed out by radiation pressure, and theother tail escapes along magnetic field lines. As thenucleus orbits, the dust particles are left behind in acurved arc. Both the gas and dust tails point awayfrom the Sun; in effect, the comet chases its tails asit recedes from the Sun. The tail can reach 150million km in length, but the total amount of materialcontained in this dramatic display would fit in anordinary suitcase.

Solar System StatisticsoPlutarshptunanusnr4,4975,9132. Period 2,7566,786.8143,200 120,00051,80049,528 2,330Hydrogen onDioxideHydrogenHelium3. EquatorialDiameter(Kilometers)4. M1. Mean DistanceFrom Sun(Millions VenusNUeptuneranusSaturnJupiter8Hydrogen Hydrogen Hydrogen MethaneHeliumHelium ?HeliumMethane Methane5. Moons00121618 (?)15816. Rings000011,000 (?)11 (?)407. Inclination ofOrbit to Ecliptic7 3.4 0 1.85 1.3 2.5 0.8 1.8 17.1 8. Eccentricity s243days9. Rotation Period26.8days23 hours 24 hours56 min. 37 min.6 days9 hours 10 hours 17 hours 16 hours 9 hours7 min. 18 min.55 min. 40 min. 12 min.retrograde10. Inclination ofAxis*7.25 Near 0 177.2 * Inclinations greater than 90 imply retrograde rotation.retrograde23 27'25 12'3 5'26 44'97 55'retrograde28 48'120

Instructions for Puzzle AssemblyMaterialsSolar System Puzzle Patterns*Cellophane tapeColored marker pens or pencilsScissorsRazor blade craft knifeButter knifeCutting surfaceMetal edge rulerWhite glue (optional)* If possible, copies of the puzzle patternsshould be printed on 60 to 100 poundweight white paper or could be glued onposter board. Otherwise, have the patterns duplicated at a commercial copierbusiness on heavy paper stock.7. When all cubes are assembled, put the puzzletogether. Starting with one side of the puzzleat a time, begin coloring the images of theobjects pictured. Use the coloring instructionsas a guide or have students find images of theplanets and Sun in astronomy books and try tomatch the colors in the puzzle. You can alsocolor the captions.Alternate Construction TechniquesA more rugged puzzle can be constructed by gluingthe squares to blocks of wood or other materials.Reduce or expand the patterns on a copy machine tofit the blocks. Be sure to place the squares in theproper positions so that properly oriented puzzlefaces will be created.Activities and QuestionsInstructions1. Carefully cut out each cube pattern.2. Using the razor blade knife and a cutting surfacebeneath, cut the center of the small slots oneach pattern. Matching tabs will be inserted intothese slots.3. With the metal edge ruler for a guide, use thebutter knife to score the white dashed lines oneach pattern. Be sure not to press down so hardthat the paper is cut. The score lines will make iteasy to fold the patterns precisely. Also score thetabs and flaps.4. Pre-

planet has a magnetic field, although Earth's mag-netic field is considerably stronger. However, the planet's density (5.4 g/cm3) is about the same as Earth's. Scientists think the density indicates an enormous iron core composing some 75 percent of Mercury's diameter. A rocky mantle and crust only about 600 km thick surround the core. When