NASA Facts the Voyager Mission

8/7/2019 NASA Facts the Voyager Mission

1/8

N/%S,AFactsAn Educational Publicationof theNational Aeronautics andSpace AdministrationNF-89

'^ssn^^ir

The V oyager MissionJupiter, The Giant of the Sour System

In orbit 760 million km (485 million mi) from the Sun,Jupiter is four-and-a-half times as distant from the Sunas is the Earth. The planet is unusual by earthlystandards; it is only slightly denser than water, but 318times more massive than the Earth. Because of thisgreat mass, which is more than that of all the otherplanets combined, Jupiter dominates the Solar Systemafter the Sun. Its powerful gravity pulls the - hits of theother planets c it of shape, and may have preventedthe asteroids rom forming a planet. The orbits ofcomets are Ymaffected by Jupiter ; some cometshave ever -- , ,en captured by the big planet and areunder its conli,)I.

The giant Julz i ter differs greatly from Earth and theterrestrial rocky p lanets, Mercury, Venus, and Mars, inthat Jupiter does.-.u, appear to have any solid surface,but is a great ball of liquid topped by a thin shell ofgas. It consists mainly of hydrogen, with a smallquantity of helium and traces of ammonia, methane,water, ethane. and acatylene. The interior of the planetis believed to change gradually with depth from agaseous mixture of hydrogen and heliumabout oneatom of helium for every ten molecules of hydrogento an interior of liquid metallic hydrogen. There mayalso be a small rocky core.

After the S. I n, Jupiter is also the noisiest source ofradio signals in the solar system. The radiation wereceive at Earth from Jupiter consists of three types.Thermal radio waves are produced by moleculesmoving about in the atmosphere of the giant planet.Radio waves in the decameter range are produced byelectrical discharges in the atmosphere and are some-how Influenced by the movement of one of the satel-lites, lo, along its orbit. Radio waves in the decimeterrange are produced by electrons in the magneto-sphere of Jupiter. It was these decimetric waves thatled scientists to conclude that Jupiter has a magneticfield like that of the Earth because the particles re-sponsible for generating them must be trapped insuch a field. This magnetic field and magnetosphere

of Jupiter was confirmed by NASA's Pioneer space-craft flying by the planet in 1973 and 1974.

The visible surface of Jup i ter is the top , if turbulentclouds. Estimates of the depth of the atmospherebeneath these clouds vary from 100 to 5800 km (60 to3600 mi). Below the atmospheric shell is a deep oceanof liquid hydrogen. Astronomers agree generallyabout the interns! structure of Jupiter (Figure 1), butthey differ about the deta;ls. At the high pressure deepwithin the planet, hydrogen becomes metallic in formand - eadily conducts heat and electricity. There is ashall of this liquid metallic hydrogen surrounding arocky core, which also probably contains heavier

ATMOSPHERE82% HYDROGEN17% HELIUM1% OTHER ELEMENTS

r CLOUD TOPS240 km 1150 mi l DOWN

TRANSITION FRJMGAS TO LIOU10 HYDROGEN1000 km 1600 m i l DOWN

TRANSITION FROM LIQUID HYDROGENTO L IQUID METALLIC HYDROGEN25,000 km 115,000 m i l DOWNTEM PERAT URE 11,000 C 120.000FIPRESSURE. 3MILLION EARTHATMOSPHERES

-SMALLROCKYCORETEMPERATURE 30 ,000 0 C (54.000OF)POLAR DISTANCETO CENTER66,458 km 141,483 mi l

Figural. Diagram of tho Interior of the planet ,lvpftw accordingto a com m only accepted nwdel.(NASA TM-79953) NASA FACTS: AN EDUCATIONALN79-20955PUBLICATION OF THE NATIONAL AERONAUTICS ANDSPAC ADMINISTRATION. THE VOYAGER MISSION(National Aeronautics and Space UnclasAdministration) 8 p MF A01; SOD HC CSCL 03B G3/91 19419


2/8

metals. The hell Jm of the planet might be mixed w iththe hydrogen in solution, or might have condensedinto a shell of liquid helium su rrounding the c ore. At thecore, temperatures might be as high as 30,000"C'(54,000F). Suc h a hot core could acc ount for Jupiterradiating into space some two-and-a-half times asmuch heat as it receives from the Sun.At one time astronome rs thought that Jupiter gener-

ates heat by the pressure of its own gravity com-pressing its interior and causing it to contract in size.Now some astronomers favor the explanation thatJupiter is hot today because it is still cooling downfrom its formation. As it cools it continues to contract.Jupiter is too small for the weight of its massive bulk tocompress the material at its center sufficiently to ignitenuclear reactions there. Had Jupiter been larger itmight have formed a second sun, so that the SolarSystem wou ld have become a binary star system.O rrin of Jupiter

Scientists think that the cloud of gas from whichJupiter was formed gave birth to the gian! planet about4Y2 bi ll ion years ago by a 7 0,000-year convulsive con-t ract ion that wa s fol lowed by a headlong col lapse toform the planet in a brief three months. The initial cloudfrom w hich Jupiter originated w as probably 6 50-mil lionkm (400-mil l ion m i) in diameter, but w ithin the 70,000years of initial formation it rapidly shrank and h eatedfrom a temperature of -218C (-360F) to 2200C(4000 0 F). The hydrogen molecu les ionized and brokeup, and the protoplanet collapsed within a few monthsto about five times its present diameter. As it did,enormous quan t i ties of heat were developed b y thetremendous pressures. The interior of Jupiter reacheda tempe rature of 50,00M (90,000F), and the planetglowed red h ot at i ts surface. Over the bi l l ions of years

NORTH NORTH NORTHTEMPERATE BELT -

NORTH NORTHTEMPERATE BELT-NORTH TEMPERATEBELT

NORTH EQUATORIALBELT-- -N COMPONENT ----

S COMPONENT

SOUTH TEMPERATEBELT

SOUTH SOUTHTEMPERATE BELT

SOUTH POLARREGION GREAT RED SPOT to the prebant, the planet has gradu al ly cooled. Evi-dence for this red-hot phase is thought to be thedecreasing d ensity of the big satell ites of Jupiter withincreasing distance from the planet. The innermostmoons were heated so much by the hot planet thatmost lightweight substances (volatiles) were driveninto space. Water was prev ented from condensing orremaining in any su bstantial quantities on them.Jupiter m Saan from EarthJupiter completes an orbit about the Sun in 11.86years. When Jupiter appears opposite to the Sun a sseen from Earth, astronomers s ay that the planet is inopposition. At this tir - the planet is closest to theEarth and shines its brightest in the night sky , directlysouth at midnight. During NASA's Voyager mission toJupiter, opposit ions of the planet wil l occur d uring thewinter monthsD ecember 1977 in the constellation ofTaurus, January 1979 in G emini, and Fe)ruary 1880 inCancer. Even small telescopes will reveal bands ofckwds and show the four big satellites as star-likeobjects moving in their orbits about Jupiter.Jupiter completes a rotation on its axis in 9 h,55 m in, and 30 s. This rapid rotation has flattened thepoles and bulged the equa tor of Jupiter. The polar andequatorial diameters are 133,516 km and 142,796 km(82,966 mi and 88,734 mi) respectively. Seen bytelescope from Earth, Jupiter appears as a striped,banded d isc (Figure 2), with all the ma rkings parallelto the equa tor. D usky-gray regions cover each pole.The dark, slate-gray stripes are called belts. They arebelieved to be regions of descending air masses . Thel ighter, salmon-colored bands, cal led zones, are be-l ieved to be r is ing cloudy air masses. A transparentatmosphere extends high above the visible cloud topsof the belts and zones. NORTH POLARREGIONNORTH NORTHTEMPERATE ZUNENORTH TEMPERATEZONENORTH TROPICALZONEEQUATORIAL ZONEEQUATORIAL BANDSOUTH EQUATORIALBELTSOUTH TROPICALZONESOUTH TEMPERATEZONESOUTH SOUTHTEMPERATE ZON E

Figure 2 The v ls lb is sufam of JupH w com eft of s bwxbd s t ructurs of curds tr st ars consistarde rmo to hen b ow p tvsn the nsnws s twwn In th is d r swi r r .11NAL ^PAG^i3r: ool


3/8

Among the belts and zones are ma ny sma l le r fea-tu resstreaks, wisps, arches, p lum es, and s potssome of which m ay be knots o f c louds. They changeform rap id ly even though they are thousands of k ilo -meters in size. T h i s i nd ic a tes a v e r y tu r b u l en tatmosphere.

The c loud features move around Jupi ter m ore slowlyat i nc reas ing d is tance f rom the e qua tor . A g rea tequatorial current sweeps around the planet some 400km/h (250 mi /hr) faster than the regions on ei ther s ideof i t. Te lescop ic observat ions show that a i r ma ssesmove parallel to Jupiter 's equator rather than from theequator toward the poles, as on Earth. Cloud motionsh av e b e en m eas u r ed i n th e zo nes th a t ind i c a tespeeds of 320 km !h (200 m i /h) re lat ive to the wholeplanet.

The ban ds around Jupi ter are explained as convec-t ive cel l s in the atm osphe re that are s t retched outbecause o f the p lanet ' s rap id ro ta t ion. At the top o fthese l igh t zones, the coo ler m ater ia l m oves towardthe equator and toward the pole and is deflected in aneast-w est direction by the rotation of the plane t beforei t s inks b ack to lower al t itude in the dark belts . Above50-deg n or th and be low 5 0-deg so uth la ti tudes, thebanded st ructure ends and the atmosphere is turbu-lent ly d isorganized into man y conve ct ive cel ls (Fig-ure 3).

In the southern hem isphere is a 24,000-km (15.000-mi) diameter oval feature known as the Great Red Spot(F igure 4), which has int r igued as tronome rs and the-orists since i t was f i rst observe d centuries ago . Thespot has va ried in intens ity. color, and size over theyears , and se vera l times i t has a lm os t comp le te l yd isap p eared . Th e re a re a lso sm a l le r red sp o ts andwhi te spots w i th in the tu rbu len t c loud sy s tem s o fJupiter.Scient ists now think they have discovered som e ofthe main features of Jupiter's atmosphe re and weather.The w ea the r p robab ly occurs in a th in sk in o f thea tmo sp h ere as i t d o es o n E a r th . Th e bo t to m o f t h eweather layer is a t the base o f the lowest c louds o fwater , be low wh ich is a re la t ive ly un i fo rm ly-heateddeep atm osphere of hydrogen and hel ium. Instead ofmoving f rom the e quator to the poles and back, as onEarth, Jupiter's weather circulation see ms to consist ofa relatively local turbulence in the polar regions, an d af low pa ra l le l to the e qua tor in the tem pera te an dequatorial regions. This mea ns that we ather circulation

on the whole p lane t is som ewha t l ike we ather in theEarth's tropical regions.The hea t rising from the interior of Jupiter appears tobe shun ted away interna l ly f rom the equator ia l re-gions, which are w arme d by incoming s olar radiat ion.The resu l t i s that the p lanet behaves as though con-trol led by a g iant thermostat so that i ts atmosphere h asa tem perature at the polar regions similar to that at theequator , and in bo th day and n igh t hem ispheres . Ifthere is, indeed, no flow of heat in the atm osphere fromthe equator toward the poles, the wea ther on Jupiter

Figure & This sn m illimuM a s Pbrnsr 11 p6cWm oovm partof JupWa north to Versb zone end IW oath paler replan. Nshows dw bwskup of dw rspulw bsrdsd strucWm of A*ftesclards nor#nvwd town the pole.

m ust be dr iven by the internal hea t , not by solar heatas on E arth.Zones a re be l ieved to be s imi l a r to cyc lones onEarth, but on Jupiter they are stretched out around theplanet (F igure 5) . Hea t re leased f rom the condensa -t ion of water within rising masses of atmosphere calledcel ls could dr ive the r is ing ce l ls eve n h igher . Morewater - laden a tmosphere wou ld be sucked in to ther is ing colum ns a nd reinforce th is ef fect.The zones m ay thus be planet-girdling, cyclone-typefeatures consist ing of long str ips of r is ing a tmospherepowered endlessly by the condensation of water vapor.There are, howe ver, other explana t ic , is for Jupiter 'swea ther systems , such as a slight equator-to-pole heatf low, and the ef fects of the huge s ize of the p lanet onthe w ay f luids f low within it . Also, the liquid interior ofJupi ter may af fect convective f low in a w ay that g ivesrise to zones in the atmos phere of differing heat, whichc a us e s t he m t o r is e a n d f a l l. T he NA S A V oy a g e rspace craf t w i ll gather new inform at ion that shouldallow scientists to choose between the various currenttheories. It seem s clear, howeve r, that the basic dif fer-ences be tween we a th e r o f th e E a r th and o f Ju p i te rar ise f rom the lack o f a s o l id sur face on Jup i ter and

ORIGINAL PAGE' 13O F PO O R QUALITY


4/8

p',wb ,4 ., ,f , * m o w n hwWW ' a Jupw owe I@ , M0004un " ova, fqw a ca end . Groo RW spot, whiMpWW for hundrtdt of yvemCRIGINAL. PAGE- I:,

4QE pMR QUALITY


5/8

D METALLIC HYDROGENJ\y A

1\}/ MOLECULAR HYDROGENtr\1OU

Figure S. Convecft petfsrns pnop mri for now of Jupft oliquid interior are shown In this dlegrrn. Now the pops, o nckcular now of liquid hydrogen by convection (rising of hwAdmaterial) Is conventional. In the equatorial rpions, howeve r,than mar be a series o f turning conve ctive roi ls, paral le l toJupiter's rotation axis. Convective flow wo uld occur In the zoneof nw sc ulw hydrogen and be unable to cross the bou ndw V Natothe region of Nq;,uid nnehNk hydrogen- C onvective now In arapidly ratstlng liquid sphere Is di ferert from That In a staticliquid.

from internal heating of the giant planet as opposed tothe Earth's heating from the Sun. Clouds and atmo-spheric features can go unchanged for decades or forcenturies on Jupiter because there is very little fictionbetween the thin cloud layers and the compressedatmospheric gas below them. There is no solid surfacelike that of the Earth to affect the flow of atmosphericgases.

Permanent features seen in the atmosphere, suchas the Great Red Spot (Figure 6) could be 'free-wheeling' phenomena that require relatively small in-puts of energy to keep them going. Jupiter's hydrogenatmosphere retains energy more easily than doesEarth's atmosphere of nitrogen and oxygen. Con-sequently, once a free wheeling phenomenon hasreceived energy, a long time can elapse before theenergy is dissipated. The Great Red Spot turns like awheel between the north and south halves of the SouthTrop i cal Zone, which is split by the spot. Over the 300years since it was first observ ,)d, the spot has driftedwestward at an irregular rate. There are smaller redspots in other zones, but these have not lasted as longas the big spot. The spot has been simulated on

Figure T3. Tin Great Red Spot, aeon In close-up by Pioneer 11,dhpiays a motried appearance within ib Interior, wNd mar beturbulent cloud systems. Odw smeft spot can be even. a by

computer models by assuming that it is a risingcolumn of gas spun between the halves of the tropicalzone in which it is located. Some scientists speculatethat this column rises to a height in the atmosphere atwhich traces ofr)sphorus can condense and there-by create its deep. od color. The top of the red cloud issome 8 km (5 mi) above the surrounding clouds.

The highest clouds on Jupiter are the deepestcolored, and the red color may be due to phosphorus.The next highest clouds are white-, believed to beammonia crystal clouds. Below these are gray orbrown clouds that may consist of ammonia and sulfurcompounds or complex organic molecules. The waterclouds, where viater condenses and releases latentheat, may form a transition region between the uni-formly mixed lower atmosphere and the upper regionof weather. (See Figure 7.)

OKIGINA'4 PAGE ISOF. POOR QUALITY.


6/8

TEMPERATURE. C

T I )I . S . B . 1y m I C H + )G R O U N D - B A S E D

12 .414 .0 ym (H 1I IND N H 3B S E R V E G R O U N D - B A S E D .C L O U D ISum(H 2 , N H 3 1 AN DN Z O N E S 2 0 P I O N E E R I RN H , S H

1 - 2 0 a mIN H 3 1 ,AN D ^ .- H 2 O I C E i .4. 5 TO 5 . 5 pm( H 2 )I2001000 100Q01( O i 1CcW0 1,01 0 . 030.0 the therm al and other proper t ies of the atm osphe re of2 0 0 ( 1 2 1 Jupi ter .1 8 0 0 1 1 2 ) The tem perature o f the upper a tm osphere of Jup i terapp ears to be h igher than would be expe cted f rom, 8 0 O W ) heat ing by incom ing solar radiat ion and outgoing heatf ro m t h e p l a n e t it s e lf . S o m e u n k n o w n m e c h a n is m, . 0 1 8 nEE could be the cau se. Po ss ib ly there i s an in terac t ionbetween par t icles in Jup i ter 's m agnetosphere an d the1 2 0 ( 7 S ) a g a se s o f th e u p p e r a t m o sp h e r e . T h e V o y a g e r sp a c e -craf t wil l t ry to resolve the quest ion by observ ing ul t ra-1 0 0 ( 6 2 1 ^ v io le t rad ia t ion f rom the p lanet 's upp er atmosphere.PPPePW ( 5 0 ) T his wil l p rov ide in form at ion about the nature of the8 0 (37) processes taking place there.4 0 1 2 5 12 0 1 1 2 100 The W"Flyrsr z. D i a g r a m o f t l w a t rr w a p h r e of Jupft r alimm nq thepoNlEon of the main cloud layers and ft tampiarobi s andprsaaame at thalr bvab w cslada1 by A. IngermA of CaNack

However, we are still quite ignorant of the true natureand origin of Cie material that makes up the colors ofthe clouds of Jupiter. The colored material mightoriginate in high temperature chemistry taking placebeneath the cloud layers and be swept to high alti-tudes by the upwelling storm systems. Full-disc colormovies of Jupiter will be obtained by the Voyager:spacecraft and may show the interactions betweencloud motions and color on the planet.

Atmospheric features on Jupiter will be tracked byVoyager's cameras in an attempt to understand themeteorology of Jupiter better. Such understanding willhelp us also understand the complex terrestrial pat-terns of weather systems. Voyager will be able to showus how the Jupiter weather features change over aperiod of time and confirm whether or not t hey areconvective storms like huge hurricanes. The GreatRed Spot and other smaller spots may be dynamicmeteorological phenomena, i.e., huge storm systems.The mottled appearance within the Great Red Spot asseen in the Pioneer pictures suggests such convectivemotion. If the Great Red Spot can be photographed atthe edge of the planet, we might be able to obtain itsprofile and find out exactly how high it pokes abovethe rest of the cloud systems. Differences in colorrevealed by high magnification imaging may provideus with clues on the composition of the clouds. On thedark side of the planet, we can also kook for lightningdischarges in an attempt to discover if these aiecauses of the decametric radio waves.

To explain the Great Red Spot, we need to find outhow the smaller red spots form and later fade bylooking at them with the high magnification possiblewith the Voyager cameras. Then we can see all thedetails of their structure and find out how these detailschange as the spots evolve. At the same time, instru-ments carried by the Voyager spacecraft will look at

The magnetusphere of Jupiter (Figure 8) in whichprotons and electrons are controlled or trapped by themagnetic field of the planet has a volume one milliontimes that of the Earth. Jupiter's magnetosphere islarge because relatively low-energy particles spinningoff from the top of the ionosphere stretch the magneticfield lines. Outflowing low-energy particles, however,can produce only a very weak magnetic field at greatdistances from the planet. High-speed gusts of thesolar wind periodically push back this weak field andforce the magnetosphere to collapse. As it does,energy is imparted to electrons and they are acceler-ated almost to the speed of light. They squirt acrossthe solar system to Earth and even to Mercury. One ofthe unexplained effects is that electrons surge outfrom Jupiter once every ten hours.

The entire magnetosphere of Jupiter behaves likean enormous, fast-rotating, leaky bag, the outer skin ofwhich moves about 2 1 12 times as fast as the 1.6 millionkm/h (1 million mi/h) solar wind, the blizzard of elec-trons and protons streaming outward . ` -om the Sun.The continuous buffeting and shaking of this hugespinning bag of particles as th q magnetosphere ofJupiter rubs and bumps against the pressure of thesolar wind, interrupts the regular movement of par-ticles from pole to pole within the magnetic field ofJupiter along the field lines, and throws them inwardtoward the planet, thereby recirculating and ener-gizing them. The magnetosphere contains radiationbelts that are 5000 to 10,000 times as intense as thoseof Earth. This tremendous intensity may originate fromrecirculation of particles with increase of their energyeach time around.

Particles from the radiation belts around Jupitermove to the turbulent outer magnetosphere along linesconnected to the magnetic poles of the planet, whichare offset from the rotation poles. There they areredirected by snarled magnetic fields and some of theparticles move back to the inner radiation belt. TheInward morion increases the energy of these p ar t ;cles.E a c h t i m e t h e y r e p e a t t h e c y c le t h e y o b t a in m o r eenergy. A l though m any o f the par t ic les are absorbedby the Ga l ilean sa te l li tes , som e even tua l l y acqui re


7/8

Figure ti. dupftes m gnatopNsn in crea I by the plsnst'spo wm! megnedc Field holdkug Ior it d pardclss of the solarwind away from the punt The megneNe AM Is at leastdoubled In sin by Ionised pertkbs from the bop of Juphar'sIorroepiren. In these peAicrt are spun out by oaKrtkooel tame,they drag the nuegruetic flab with them Jupftes nngnsbo-Wm has an .vo d arnebsr of nine ti N m muss, bigenough, M I t could be even f rom Ear th, ha l f a b i l lion mi les away,to occupy 2 d og of sky, conVered to the 0 .5 deg ooawW by theSun and the Yoon.

enorm ous ene rg ies and squ i r t ou t f rom Jup i te r acrosst he So la r Sys tem.The rad ia t ion be l ts o f Jup i ter wo uld probably be 100t ime s m ore i n tense w i thou t the sw eep ing e f fec ts o f theGalilean satellites and the squirting of particles intointerplanetary space. The particles in the radiationbelts probauly come from the top of Jupiter's iono-sphe re ra the r than f rom the so la r w ind . By con t ras t ,Ear th 's rad ia t ion be l ts a re mad e up o f par t i c les f romthe so la r w ind t rapped by Ea r th 's magne t ic f ie ld .The magnetosphere of Jupiter has three distinctregions. The inner magnetosphere, like that of theEar th, is doughn ut shaped with the planet in the hole. Itcontains the intense, multishelled radiation belts inwh ich three of Jup iter 's b ig moon s orb i t and constant ly

sweep out particles. This inner magnetosphere ex-tends ab out ten d iam eters f rom Jup i te r ; i. e . , to abou t1,400,000 km (900,0,00 m i) .A m i dd l e mag ne tos phe re c on ta i ns a c u r ren t s hee to f e lec t r if ied pa r t ic les mo v ing ou t f rom Jup i te r unde rcentrifugal force, thereby stretching magnetic fieldl ines w i th them . Th is d isc ex tends be twee n 10 and 30diam eters of Jupi ter , to abou t 4 ,300,000 km (2,700,000mi). These particles, which in the middle magneto-sphere a re mo s t l y e lec t rons , tend to be con f ined to at h in cu r ren t shee t l ike a r i ng a rou nd the p lane t .

An outer magnetosphere lies between 30 and 45Jup i te r d iamete rs (up to 6 ,400 ,000 km o r 4 ,000 ,000m i ), bu t bu f fe t ing by t he s o l a r w i nd c aus es t he m ag-netic fields to be irregular and the size of this region tof luc tua te w ide ly a t d i f fe ran t t imes.The space cra f t P ioneer : 10 and 11 orov ided mu ch

in format ion abou t th is mag net ic environme nt of Jupi ter ,wh ich co n ta i n s th e p l a sm a o f e l e c tro n s a n d p ro to n ss u r round i ng t he p l ane t , and a l s o how t ha s o l a r w i ndinteracts with it. The Voyager spacecraft in turn aree x p e c te d to p ro v id e e ve n b e t te r a n d m o re co m p le teinformation about the region, including the positionand shape of the bow shock. This shock is createdwh ere the m agne t ic f ie ld o f the p lane t ove rr ides thef ie ld car r ied by the so la r w ind . The Nvo P ioneer space -craf t observed t remendous var ia t ions in the locat ion ofthe magn e topause reg ion be tween the so la r w ind andthe field of the planet. These variations are still nott ho rough ly unde rs tood . The p ressu re o f the s o la r w indvaries a greai deal at different times and it could bethat these changes cause the fluctuations in thema gne topause observed by the P ioneers . To th is end ,t he Voyag ers ' ins truments w i ll a t t empt t o de te rm ine theextent and the phy sica l character ist ics o f the e lect ronsand ions fo rm ing the p lasma w i th in t hese th ree reg ionso f t he m agnetosphere , par t icu la r ly where the e lec t ronsc hange f rom be i ng pa r t o f t he inne r m r .gna tos phe re ,wh ich ro ta tes w i th the p lane t , and the reg ion wh ich i sinfluenced by outward current flow to become am agne to ta i l s t reaming be h ind the p lane t i n a d i rec ti onaway from the Sun. The tail has been detected as farawa y as the o rb i t o f Sa tu rn .

An important discovery of the Pioneer spacecraftwas the s t rong ly d is to r ted na tu re o f t he ou te r m agneto-s phe re . T he gen e ra l th ree -d im ens i ona l s hape o f t hem agne tosphere i s s t i l l no t tho rough ly unders tood , be-cause i t i s com p l ica ted by the rap id sp in o f the p lane tand the e f fec ts o f the so la r w ind bu f fe t ing the m agne-tosphere . The Voyag er miss ion w i l l p rov ide two m oretracks of spacecraft through the complex magneto-sphere an d thus p rov ide a be t te r bas i s fo r ou r under -standing o f .Jup iter 's in teract ion w i th the so lar wind.

There i s a conce nt ra t ion o f l ines o f m agne t ic fo rcethat extends from the surface o f Jupiter to the satellitelo . Th is is re ferred to as a f lux tube an d i t is som ehowconnected with the emission of radio waves fromJupiter . The or ig in of these decametr ic radiat ion burstsf rom Jup i ter is s t i l l unkno wn , but i t is bel ieved tha t theymay be connected in some way with instabilities ofp lasm a w i th in the ionosphere o f Jup i te r wh ich are , inturn, caused by a flow of energy down the flux tubefrom lo. Scientists speculate that these enormoussurges of energy might be detected by Voyager asu l t ravio le t em issions on the n ight s ide of Jup i ter . Also,one o f the Voyag er spac ecra f t w i !I f ly th rough the f luxtube and p rov ide i n fo rma t ion abo u t i ts t rue na tu re andthe energy f low ing a long i t .

ORIGINAL QV^r.^OF P ^


8/8

S T U D E N T I N V O L V E M E N TP r o j e c t O n e : T h e M a g n e t o s p h e r eConstruct a m iniature model of a magnetic f ie ldshowing the f ield l ines by placing a bar m agne tbeneath a shee t of white paper and then sprinklingiron filings on the paper. Shak e the paper slightly andthe iron filings will align themselv es along the charac-teristic field lines. T his shows the field two-dimension-ally. T o ex plore the three-dimensional field around aplanet such as Jupiter , a m odel can be m ade byinserting a bar magne t through a hole in a rubber ofstyrofoam ball. The d iameter of the ball should be thesame a s the length of the bar magnet.Trace the mag netic field lines around your mo delplanet by use of a sm all compass or a dip needlemade by magnetizing a short length of iron and sus-pending it by pins so that it can ro tate on a horizontalaxis.Dem onstrate planetary rotation effects by sus-

pending the ball representing the planet on a piece ofthin twine. Tilt the axis of the bar ma gnet so that it is11 de grees from the vert ical axis about which theplanet will rotate. Now observe what happens to thecompass needle and the dip needle when they areplaced at a fixed position a short distance from theplanet and the planet is rotated. Your ooservationpoint (the locat ion of the compass and d ip meter)represents a spacecraft at a point on its path throughthe magn etosphere of the planet. Repeat your ob-servat ions at se veral d i f ferent points on a f lybytrajectory.Ne xt suspend the planet model so that the barmagnet is vertical. O bserve what happens when theplanet is rotated about the same a xis as the barmagnet . Do the compass a nd dip needle behavedifferently or the sam e?P r o j e c t T w o : T h e A t m o s p h e r e

If organic molecules are discovere d to be responsi-ble for at least som e of the colors in the clouds ofJupiter, it might be that organic chemistry could flour-

ish beneath the clouds where temperatures may bethe same as on Earth. Find out from F i ,40 re 7 the depthbelow the water ice clouds where the temperature isthat in your classroom . W hat is the pre.;suie in Jupiter'satmosphere at that !evel according to f = igure 7? Is thispressure too great or too sm all for terres t rial life forms?From your knowledge of how weather .;irculates onJupiter, describe what a Jov ian ;ire `orrl m ight be like.H ow would it move around? W hy would it have to movearound? W hat might it eat, it how otherwise could itderive energy for its life processes?

S u g g e s t e d R e a d i n gINTERPLA NET ARY PARTICLES AND FIELDS. J. A.Van Allen, Scient i f ic American, v. 23 3, Septem-ber 1975, pp. 160-173 .JUPITER, J . H . W olfe, Sc ien t if ic Am er i can ,v233,

September 1975, pp. 118-126.JUPITER'S A TM OSPH ERIC CIRCULATION, G. P. W i l-liams, Nature. v. 257 , October 1975, p. 778.JUPITER; SOME CONCLUSIONS AND QUE STIONS,G . Hunt and E. Burgess, New Scient is t , v. 68,November 1975, pp. 32 6-32 7.NEW STUDIES O F JUPITER, W . B. Hubbard, and J. R.Jokipii, S ky and Telesc ope, v . 50, October1 9 7 5, po. 212-216.PIONE ER O DYSSE Y, R. 0. F immel, W. S windell , andE. Burgess, NASA SP-3 96, W ashington, D.C.,1977.Reports of all the Pioneer 11 science experiments,var ious authors, Science, v. 188, M ay 1975,pp. 445 -477 .TH E M ET EO ROLO G Y OF JUPITE R, A. P. Ingerso ll .Sc ient i fi c Am er ican, v. 23 4, M arch 1976, pp.46 -56 .

This is the third in a series of publications on the Voyager mission toJupiter and Saturn The first publication In the series was entitledLoyager, Mission to the Outer Planets. the second was entitledSa te l li tes o f the Outer Plane 's ; a future Issue will be devoted to theplanet Saturn

For sale by the Superintendent of Documents, U.S. Government Printing ()MeeWashington, D.C. 2 M0 ' 2

Stock Number 033-000-00 53-1

* U.S . GOVERNM ENT PRINTING OF FICE : 1970 0 -281-717 (5703)