a new look at jupiter results at the now frontier

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A N E W M N W A T 3 1 1 1 4 T E R :

AT THE N1'W FININTIER

ENCOUNTER

Pioneer '10 hurtled 81,000 miles above

the cloud tops of Jupiter, giant of theSolar System, at 6:26 p.m. PDT on De-

cember 3, 1973. But the total period ofeneonnter with the largest planet and itsminiature solar system of 12 largo and

small satellites lasted for several months.Inbound, Pioneer 10 crossed the orbit ofthe outermost satellite, Hades, onNovember 8, Outbound, the spacecraft

obtained its final Pmage of Jupiter on N ewYears' Eve 1973 as Pioneer 10 headed tothe outer Solar System and onward into

Interstellar space, m an's first emissary tothe stars.

Scientists have analyzed some of thevast quantity of new information radioedto Earth by Pioneer 10., This sixth In aseries of leaflets on the Pioneer missionsumm arizes results of the science exper-iments. But Pioneer 10 will continue togather information about the outer SolarSystem until it passes the orbit of Uranuswhere its radio signals will become toofaint to be received by the big antennasof the Deep Space Net: the time, 1980;

the distance from Earth, almost 2 billion

miles.

Pioneer results have contributed to anew understanding of the Solar Systembeyond Mars, of interplanetary spaceand the asteroid belt, and of the envi-

ronment of the Jovian system. Pioneer10 also provided new information aboutJupiter and Its big satellites.

INTERPLANETARYSPACE BEYOND THE

ORB IT OF MAR S

COSMIC RAYSCosmic rays are actually particles, thecharged nuclei of atoms, moving at veryhigh velocities and therefore possessinglarge kinetic energy. Low energy cosmicrays seem to be prevented from enteringthe inner Solar System, possibly by scat-tering regions of the solarwind. This windconsists of streams of electrons and pro-tons and other ionized atoms emitted by

the Sun. Fast and slow streams interactto produce m agnetic scattering regions ininterplanetary space which wou ld scatterlow energy cosmic rays. Pioneer 10shows that to a distance of at least five

times that of Earth from the Sun (5 as-tronomical units) scattering regions are

being generated and no significantnumber of low energy cosmic rays enter

that Pioneer 10 will be able to detect suchcosmic rays, shou ld they exist In interstel-lar space, until the spacecraft has

reached 20 to 30 astronomical units,where the solar wind scattering regions

mo st likely subside.

N low energy cosmic rays are deteL'..J byPioneer, they will help to throw light onthe Y uzzle of why the flow of cosmic raysInto toe Solar System is about equal inenergy to the incoming light from all the

stars, whereas the output of cosmic rays

from our Sun Is only small compared withits output )f light energy. Scientists have

speculated that the Inpouring cosmicrays from We Galaxy might be purely alocal effect from the violent explosion ofan abnormal star or group of stars In ourpart of the Ga xy Alternatively the in-tense cosmic ray flux may be the residueof charged partiles from the explosivedeath of stars formed billions of years be-fore the Sun and now extinguished, par-ticles that became trapped In the mag-

netic fields of the Galaxy.

Scientists found, too, that the solar wind

streams change as they move out fromthe Sun. At the distance of Jupiter thehigh speed gusts level out and the solarwind becomes less variable than atEarth's orbit. Stream en ergy is convertedto heat energy with the result that the

solar wind does not cool dow n as rapidlyas might be expected.

Additionally, the science experiments of

Pioneer 10 recorded an interstellar windflowing into the Solar System along theplane of the Earth's orbit. This' interstellarwind, consisting of uncharged hydrogenatoms together with a smaller quantity ofhelium atoms, originates from the gas be-

tween the stars.

DEBRIS IN SPACE

Sunlight reflected from and scattered bydust particles in space produces faintglows in the dark sky known as theZodiacal Light and the Gegenschein, orcounterglow. An astronomical theory thatthe Gegenschein, which is opposite tothe Sun in the sky, might consist of sun-

light reflected from small particles inspace beyond Earth's orbit, was con-firmed. Its faint glow extends evenbeyond the orbit of M ars and Into the as-teroid belt, but not beyond. Scientistsalso found that the Zodiacal Light de-creases, as does the Gegenschein, withincreasing distance from the Sun, exceptfor some brightening within the inner

Zodiacal Light is concentrated in theInner Solar System, and It fades almost

completely at just over 3 astronomical

units from the Sun.

The 175 million mile wide asteroid belldid not prove to be as hazardous tospacecraft as some speculations hadsuggested prior to Pioneer 10's epic voy-age. Some astronomers had theorizedthat collisions of asteroids over billions ofyears might have produced a zone of de-structive dust particles. Pioneer 10

penetrated the asteroid belt safely andemerged undamaged. So did Its sisterspacecraft, Pioneer 11. The asteroid beltis not a serious hazard to spacecraftpassing through it.

However, Pioneer 10 did find a concen-

tration of dust particles around Jupiterwhich, although not a hazard to Pioneer-type flybys, might represent a danger tospacecraft in some orbits about Jupiter.

THE JOVIAN SYSTEM

SIZE OF JUPITER

Pioneer 10's path through the Jovian sys-tem, observed by tracking and analyzingchanges to the spac ecraft's radio signal,reveals that Jupiter, together with itssatellites, is heavier than previously cal-

culated by about twice the mass ofEarth's M oon. Jupiter itself is 317.8 E arthmasses—about one Moon mass heavierthan previously thought. The Earth con-

tains 81 M oon masses.

A new measurement of the diameter of

Jupiter and of the planet's polar flatteninggives the polar diameter as 82,967 milesand the equatorial diameter, 68,734

miles. Jupiter is ten times as flattened asIs Earth, probably because it is nearly allliquid and is rotating very rapidly. An ob-ject on the topmost clouds of Jupiter atthe equator travels at 22,000 miles perhour because of the plane t ', spin, com-

pared with only 1,000 miles :^r hour for

an object on Earth's equa tor. Centripetalforces oppose gravity and allow the



Figure 1 Ganymede. Jupiter a largest satellite.

THE GALILEAN SATELLITES

Pioneer 10 provided new informationabout the large s atellites of Jup iter, oftenreferred to as the Galilean satellites In

terms of the mass of Earth's Moon, thebig Jovian satellites are, lo. 1.22, Europa,0.67, Ganymede, 2.02, and Callisto. 1 44lunar masses. The new measurement ofthe mass of to is 22 percent greater thanbefore Pioneer 10

The density of the big Jovl -in satellites

decreases. like the planets, with increas-ing distance from the central body. lo'sdensity is 3.5 times that of water, Euro-pa's, 3.14; Ganymede's , 1.94, and Callis-to's 1.62 The two inner satellites mightaccordingly be rocky bodies swept free ofwater ice by primordial heat of Jupitersoon after the big planet formed, whi'e

the outer satellites might contain a large

proportion of water ice. All the satellitesnow have very cold surfaces, even ontheir sunlit hemispheres the temperatures only - 245f.

Pioneer 10 obtained images of

Ganymede (Figure 1) and of Europa.Ganymede has large flat circular plains.

hundreds of miles across, somewhatsimilar to those of Mars, Mercury, and theMoon. There are also bright and darkareas on the satellite, and markings thatmight be impact craters. Europa was toofar away from Pioneer to provide an

image showing more than vague mark-ings, like a view of Mercury as seen fromEarth.

MAGNETOSPNt Rt STREAMS OUT

IN COMFTLIRF TAM

AWAT F R O M SU NMAGNt T

AtIS

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MAGNE T IC LINES Of FOIICF

r,:•

Axis

aROTATRIN

THE MAGNETIC FIELDOF JUPITER

Like the Earth, Jupiter has a magnotic

held Pioneer 10's measurement shows

that this field at Jupiters cloud tops isprobably ten times the strength of Earth'ssurface held. The Jovian magnetic held istilled abou t 10 degree s to the axis of rota-tion of Jupiter (Figure 2), and the centerof the field is offset from the center of theplanet about 1,320 miles north and 4,850miles out toward the equator. Because ofthe tilt, a passing spacecraft sees thef ield wobble up and down through an arcof 20 degrees once every 10-hour rota-tion of the planet.

A magnetosphere surrounds Jupiter, asone surrounds the Earth, and protectsthe planet from the solar wind. And like

the Earth, Jupiter has a bow shock pro-duced when the high speed solar wind,carrying its magnetic field, interacts withthe strong magnetic field of Jupiter The

solar wind is abruptly slowed down.thereby increasing its temperature ten

times.

Between the magnetosphere and thebow shock is a turbulent region called themagnetosheath in which t he solar wind isdeflected around the magnetosphere Allthese phenomena are experienced onJupiter on a scale vastly greater thanaround Earth. Pioneers points of cross-

ing Jupiter's bow shock showed it to beabout 16 million miles wide along thetrajectory. But the magnetospherestretches three-dimensionally aroundJupiter and if it could be seen from Earthas a visible object it would appear fourt imes as big as the Sun or M oon appearsin Earth's skies.

A s Pioneer 10 hurtled through the Joviansystem it passed behind to and was oc-

culted. Ar, the spa-,ecraft's radio signalsto Earth p , ,sed through the atmosphereof to they were changed, and from thechanges scientists are able to determinethat lo's atmosphere is 20.000 times le,_

dense than Earth's atmosphere, butreaches some 70 miles above the satel-lites surface. lo's ionosphere was dis-covered to be 450 miles high above the

dayside of the satellite, which makes to aunique body in the Solar System be-cause it possesses an ionosphere while

immersed In the strong magnetic f ield ofits mother planet Scientists were sur-prised to discover that to is also embed-

ded in a vast cloud of hydrogen gas thatextends a third of the way around theorbit of the satellite.

MAGMETOSPNERE

-NOUNDAPT

SNEET OF

IO N IZED PAIITIGLES

I NERGETICcup RENI SNEETPARTICLESCREATED DTISCAPE

MOVING PART ICLES

`O U T F R

i_'• / //RADIATION DELTI-^._— =ii

TO SUN

INNER RADIATION DEL

Dow SHOCK

The magnetosphere consists of an innerregion shaped something like a



side of the doughnut ring is an unusual

outer region caused in part by Ionizedgas being thrown into space as a con-

sequence of the magnetosphere's rapidrotation with the planet. Very differentfrom Earth's magnetosphere, this outerregion is flattened. Within It Ionized parti-cles form an electric current sheetaround the planet, a sheet which flopsaround like the brim of a fedora hat asJupiter rotates Its tilted magnetic field.

At times the solar wind pushes strongly

on the magnetosphere so that the outermagnetic field collapses and accelerateslow energy particles to such high veloc-ities that they are s quirted in pulsar-likejets from Jupiter. A new discovery byPioneer 10, these particle jets make Jupi-ter the second source in the Solar

System—the Sun being the first—of highenergy particle radiation. Scientists havenow confirmed that these particles have

been detected at Ea rth's orbit for severalyears, but before Pioneer's discovery,

their origin was unknown.

Jupiter's inner magnetic field extend3from the center of the planet to about880,00 0 miles, wh ile the outer field variesbetween 2 and 4 million miles or more.

Because the poles of Jupiter's field are

reversed compared with E arth's poles, anorth-seeking magnetic compass would

point south on Jupiter.

RADIATION BELTS

Particles from the solar wind, trapped in

the magnetosphere of Jupiter, p roduce

radiation belts as they do in Earths mag -netosphere (Figure 3). An inner belt cor-responds to the inner magnetosphere

and traps electrons and protons of a w ide

ranga of energies. Intensities are some

10,000 times greater for electrons there

than in Earth's belts. Protons are severalthousand times as intense as In Earth's

bells. Such high radiation Intensitieshave previously been measured onlyafter a nuclear explosion in Earth's upperatmosphere.

In the outer belt, corresponding to the

brim of the fedora, a region of highenergy electrons is surrounded by an ex-tensive cloud of less energetic protonsand electrons.

While Earth's Moon is far beyond E arth'sradiation belts, the large Galilean satel-

lites of Jupiter (I, II, III, and IV) are im-

mersed In the Javian belts and sweep upparticles, thereby reducing the total radi-ation near Jupiter to many times lessthan what it would be without the pres-

ence of the satellites.

JUPITER'S INTERIORPioneer 10 has shown that Jupiter is a

huge spinning ball of liquid hydrogenwithout any detectable solid surface. Theplanet may have a small rocky core, but

this is still uncertain. Also, Jupiter wasprobably very much hotter when firstformed. B illions of years ago its radiationwas probably intense enough to sweepits ' inner satellites free of w ater ice, leav-

ing them den ser than the outer satellites.

Jupiter's gray-white zones are cloudridges of rising atmosphere circling the

planet. They project about 12 milesabove the belts which are cloud troughs

of descending atmosphere.

Jupiter is too hot to solidify. It is almost

certainly nearly all liquid with its atmos-

phere being only about 1 percent of its

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Figure 4. Pioneer 10 confirms models of Jupiter

that suggest the planet Is nearly all liquid with a

very small core and a deep atmosphere.

total mass. The planet is about 82 to 87percent hydrogen and 12 to 17 percent

helium, with traces of other gases suchas ammonia and methane. The atmos-phere is probably not more than 600

miles deep. At its bottom there is not aliquid surface like Earth's ocean, but agradual transition from gas to liquid at atemperature of about 3,600''F (Figure 4)..Al 1,800 miles depth, Jupiter is entirelyliquid, while at 15,000 miles below the

cloud tops the pressure from the weightof hydrogen above is so great that liquidhydrogen changes into a form whichreadily conducts heat and electricity andis called metallic hydrogen. But 'it'is still aliquid because temperatures are toohigh—estimated at 20,000'F—for hy-drogen to become a solid.

Radiating heat at 2.3 times what it re-ceives from the Sun, Jupiter loses heat

into space at an enormous rate. Temper-ature at the center of the planet must beabout 54,000'F to maintain the h eat flow.This Is six times the temperature of the

bright surface of the Sun (the photo-sphere). But at the cloud tops of Jupiter

the temperature is only –184°F. Be-tween these two extremes there m ust bevast regions of Jupiter where tempera-tures could be suitable for life, providingsuch life could live in a hydrogen rich at-mosph ere and resist rising and failing air

WIDE SPECTRUM O FLOWER ENERGY ELECTRONS

1 1 °

COMPLETE SPECTRUM

OF PROTONSAND ELECTRONS/

Iv

CONCENTRATION

OF HIGH ENERG YELECTRONS



OVIGINAL PAGE LS

OF hVit QUAL"

JUPITER S W EATHER

Spin-scan image-, of Jupiter provided

close-ups not possible from Earth (Figure

5 and 6) and allowed scientists to under-stand the circulation patterns in the Jo•

vian atmosphere Clouds form in Jupi-

ter s atmosphere by condensation as

they do on Earth But Jupiter s clouds areprobably of ammonia and ammonium

compounds as well as water The top-most clouds Pie thought to be crystals of

ammonia



ZONE

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D I R E C T I O N O F R O T A T I O N

Figure 7, Atmosphere gas, w hich would move toward the equator by convection, instead, due to canons force, moves around the planet against the direction ofrotation. Gas which would m ove toward the poles Instead mo ves around Jupiter In the rotation direction.

The semi-permanent belts and zones ofJupiter (Figure 7) seem s'im 'i lar to E arth'scyclones and anticyclones—regions of

rising and falling gas—distorted byforces produced by the rotation of the

planet coupled with movements of the

atmosphere up and down and northwardand southward. On Earth these forces,known as corlol is forces, pro duce the cir-cular wind patterns of cyclones and an-ticyclones and trade wind patterns. OnJupiter the forces are much greater andstretch the cyclones and anticyclonesaround the planet into the distinct belts

Sputs on Jup iter, including the Great R edSpot, are now thought to be hurricane-type features consisting of groups of per-sistent thunderstorms. Pioneer 10 allso

confirmed that red spots which havebeen seen for so m e tim e in the northern

hemisphere of Jupiter are small replicasof the Great Red Spot. They behave asascending masses of gas flowing outfrom tops which poke several milesabove surrounding clouds.

Jupiter duffers from Earth in its cloud pat-terns because the energy droving them

is evenly distributed night and dayaround the planet. By contrast, Earthsweather patterns derive their energy fromthe Sun which Is concentrated in thetropics on the dayl ight hem isphere of theplanet. It is because of the internal

energy source that prominent weathersystems on Jupiter, such as the GreatRed Spot, can last for many years.



F U T U R EP O S S I B I L I T I E S

As a result of information gained by

Pioneer 10's encounter with Jupiter,space mission planners can now devise

trajectories for spacecraft that take themquickly through the regions of 'intenseradiation. They now know how tosafeguard spacecraft that are to use thegravity slingshot of Jupiter to reach the

outer planets of the Solar System..Pioneer 10 has thus opened a gateway tothe outer planets.

Pioneer's confirmation that Jupiter has awarm extended atmosphere of hydrogencauses space experts to enthuse about

opportunities for further exploration of thegiant planet. Measurements of the envi-ronment of the Jovian system haveshown that spacecraft can be placed intoelliptical orbits around Jupiter and sur-vive. And the hydrogen rich, hot atmos-

phere, makes it feasible to use probes

dropped from such an orbiter to pene-trate deep without burning up. Suchprobes stand a good chance of survivingentry into the atmosphere and makingmeasuremen ts within i t.

They might even sample the Jovian at-

mosphere. Since some modern theoriessuggest that Jupiter may have formedbefore the Sun itself, Pioneer 10's explo-

ration of Jupiter may have opened theway to sample material from the proto-

solar nebula.

S T U D E N TI N V O L V E M E N T

1. An Exercise i n Encoun te r b y Se n so r s ;

For this classroom project the teachershould provide three pairs of objectssuch a% a) football and Inflated rubberballoon, b) clear bottle containing vinega rand clear bottle containing cold coffee,

and c) block of natural sponge and blockof plastic foam rubber.

The objects are screened from the classin general and each student 1s allowed toinspect them individually and make notesof his observations by three sense% firstsight, next touch, and third, smell. Thestudent is asked to write down a d escrip-tion of the ob t ects in terms of these threesensors and to describe how the objectsIn each pair diffeet

The student i j finally asked to write ashort report tsxplain'ing how this exerciseis an&9nas to a spacecraft's instru-

ments probing a distant planet to deter-mine its physical characteristics andcomposition.

2. Defining Environments; IndNiduaistudents are asked to compile a tableshowing the way in which the studentwould express the environment in termsof the five senses sight, touch, taste,smell, and hearing, for the follow'ong:

a) Surface of the Sunb) Land surface of the Earthc) Interplanetary spaced) The asteroid belte) Atmosphere of Jupiterf) Radiation belts of Jupiter

g) Interstellar space.

The student his also asked to describe

what 'important elements of the environ-merit would be missed by observations

with the five human senses in e ach of theabove.

F U R T H E R R E A D IN GS U G G E S T I O N S

Various authors, SCIENCE„ hernrts of

the science experiments and groundbased experiments with Pioneer 10, v.163, January 25, 1974, pp. 301-324..

Simmons, H.To, Wg hty Jupiter Could bea Star that Didn't Make Ito SMITHSON-

IAN, v. 5, no. 6, Sept. 1974, pp. 30-39.

Gehrels, T., The Flyby of Jupiter, SKYAND TELESC OPE, Feb. 1974.

Burgess, E., Space Probe, The PioneerJupiter Spacecraft, McGraw-Hill Scienceand Technology Yearbook, 1975.

Flmmel, R.O., Sw'IndeVl, W.., and Bur-

gess, E., PIONEER ODYSS EY, Encoun-ter With a Giant, NASA Special Publica-

t ion SP-349, GPO, 1974 „

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a new look at jupiter results at the now frontier

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