Mars Student Imaging Project - Mars...

MARSSTUDENT IMAGING

PROJECT

Resource Manual

Mars Education ProgramJet Propulsion LaboratoryArizona State University

Version 2.00

The Mars Student Imaging Project

Written and Developed by:

Keith Watt, M.A., M.S.Assistant Director

ASU Mars Education Program

Image Processing Curriculum by:Sara Watt, M.S.


Editing by:

Paige Valderrama, M.A.Assistant Director


Sheri Klug, M.S.Director


(C) 2002 ASU Mars Education Program. All rights re-served. This document may be freely distrubuted for non-commerical use only.

MARS STUDENT IMAGING PROJECT RESOURCE MANUAL1

with the theory, however. Careful ob-servations showed that the planets didnot quite move in perfect circles.Faced with an observation that couldn’tbe explained with current theories,Ptolemy modified Eudoxus’ theory andreplaced his simple circles with a com-plicated system of “epicycles”, circlesthat interlock like gears in a complexmachine. Ptolemy’s theory could de-scribe and predict the motions of theplanets with an accuracy never beforeachieved. For almost 1,400 years,until the 16th century, Ptolemy’stheory was considered to be the onlycorrect theory of the Universe. Thetheory was endorsed by the CatholicChurch, which declared any other ex-planation for the planets’ motions tobe heresy and punishable by death.

Ptolemy’s theory only had one prob-lem: it was wrong. One hundred yearsafter Eudoxus, the astronomerAristarchus watched the shadow of theEarth sweep across the surface of theMoon during a lunar eclipse. His ob-servations showed that the Sun hadto be much larger than the Earth, andhe felt that it was not likely that a large

In the BeginningScience and our view of the worldchange only when we are presentedwith some observation we can’t ex-plain. Early Greek scientist-philoso-phers believed that Earth was at thecenter of the Universe and all othercelestial bodies revolved around it.Eudoxus, a mathematician who livedin the fourth century B.C., was one ofthe first people to propose this theory.Eudoxus’ version of the theory was el-egantly simple: God is perfect, theonly perfect forms are circles, there-fore the Sun and planets must movein circles around the Earth. ClaudiusPtolemy, a Greek scholar who lived inAlexandria, Egypt, around 140 ADnoted that there were some problems

Chapter 1: Mars in Society and Culture

Mars has always played a significant role in human society. The early Greeksnoted that unlike the other planets, Mars sometimes seemed to reverse itsdirection across the sky. This “contrary” motion suggested disorder and anar-chy to the Greeks, which, along with its reddish color, led them to name theplanet after Ares, their god of war. The Romans later changed the planet’sname to that of their god of war, Mars, and the name has remained ever since.

The Ptolemaic UniverseCredit: University of Tennessee


Sun would rotate around the smallerEarth. He proposed instead that theEarth revolves around the Sun. Hewas condemned for heresy because ofhis theory and all of his writings wererounded up and destroyed. The onlyreason we know anything aboutAristarchus at all is because he is men-tioned in the writings of the greatmathematician Archimedes. No otherscientist was willing to risk the wrathof the Church by mentioning theastronomer’s work. In 1543, nearly2,000 years later, however,Aristarchus’ theory was taken up byPolish doctor, lawyer, and part-time as-tronomer Nicolaus Copernicus.Copernicus’ careful observations couldnot be explained by Ptolemy’s theory.Only if the Sun were at the center ofthe Solar System could his data makesense. Once again, because of newobservations, new science and a newworldview was born.

The New ScientistsMars played a major role in the con-troversy. Even Copernicus’ theorycould not explain the strange motionsof Mars. In 1600 Tycho Brahe had un-dertaken the careful study of Mars’ or-bit. Tycho was perhaps the greatestobservational astronomer the worldhas ever known. We can make moreaccurate observations today only be-cause we have more accurate instru-ments. Tycho was world famous, arock star of science who toured thepalaces of kings and other nobility allover Europe. Tycho had given his stu-dent, a German mathematician named

Johannes Kepler, the task of creatinga mathematical description of Mars’ or-bit. Tycho, however, was very protec-

tive of his data,

Johannes Kepler (1571-1630)Credit: University of St Andrews, Scotland

the table. When Tycho finally died sev-eral years later, Kepler broke intoTycho’s safe and stole all of his data.Tycho’s family demanded the docu-ments be returned, and Kepler did so– but only after he had made exactcopies of all of the precious data.Kepler, like most of his fellow scien-tists, felt certain that the planets trav-eled in perfect circles. After years ofstruggling with Tycho’s observations ofMars, however, he finally reached theinescapable conclusion that all thework done before him was wrong: theplanets move in ellipses, not circles.In addition, he discovered two otherlaws of planetary motion that he pub-lished in 1609. Thanks to Mars, wenow understood not only its motion,but the motion of the entire Solar Sys-tem as well.

In 1634, Kepler published a book calledThe Dream, in which he described afanciful flight from the Earth to the

as are many sci-entists today.He would throwout an observa-tion over dinnerin casual con-versation, whichKepler wouldf r a n t i c a l l yscrawl down in anotebook thathe kept under


Moon. It was one of the first works ofscience fiction. Science fiction bookshave spurred generations of people towonder about the stars and the plan-ets that travel through the heavens.By the end of the 19th century, how-ever, improved telescopes showed thatthe Moon was a barren, desolate place,a place where no life could possiblyexist. Mars, however, was still a fuzzydisk in even the best telescopes. Sci-ence fiction authors, scientists, and theimaginations of the general publicturned away from the Moon and lookedinstead to the Red Planet. In 1877,Italian astronomer GiovanniSchiaparelli observed a series of linesthat seemed to cross most of the sur-face of Mars. In his notes, he calledthese lines canali, an Italian word thatmeans “channels”. American amateurastronomer Percival Lowell, however,translated the word as “canals”, a verysimilar meaning, but one that has verydifferent implications: “canals” impliesintelligence. Lowell believed thatSchiaparelli had discovered the engi-neering works of a dying Martian so-ciety desperately trying to bring wa-

ter from theMartian icecapsto the equatoriallands. Lowellwas so excitedby the discoverythat he had astate-of-the-arto b s e r v a t o r ybuilt in Flag-staff, AZ, spe-

cifically to study Mars. His writingsignited the imagination of generationsof people around the world, includinggreat science fiction authors such asEdgar Rice Burroughs (the Barsoomseries of 11 novels), Ray Bradbury(The Martian Chronicles), and H.G.Wells (The War of the Worlds). Wells’work was made even more popularwhen Orson Welles (no relation to H.G.Wells) and his Mercury Theater on theAir performed the most famous radioplay in American history. To celebrateHalloween of 1938, Welles adaptedThe War of Worlds, a tale of a Martianinvasion of the Earth, into a radiobroadcast. Story events were pre-sented as “news broadcasts” report-ing New York City in flames and un-stoppable aliens destroying everythingin their paths. Millions of people, whotuned in to the play late, thought thebroadcasts were real and fled theirhomes in terror of the “invasion”. Mosthad taken to the streets in panic andnever heard the play’s end and Welles’wish for them to have a happy Hal-loween. NBC issued a public apologythe next day; Welles became one ofHollywood’s most successful actors.Mars, and the possibility of life there,was so firmly ingrained in the mindsof the public that no one questionedthat the events of that night might nothave actually been real. Mars has al-ways had this power over us.

Today scientists know that Mars in itscurrent form probably cannot supportlife as we know it. Spacecraft sent toLowell’s drawing of Mars

Credit: The Wanderer Project


Mars have found no trace of Lowell’s“canals” or of his dying civilization. Butwas Mars always as it is now? Datareturned from our Mars spacecraftshow us that it almost certainly wasnot. At some time in the past, Marswas much warmer and wetter than itis today. What happened to Mars? Did

it once have life? Where did all thewater on Mars go? Could Earth alsochange as Mars has? These are just afew of the questions scientists hopeto answer, important questions thatyou will also help to answer as youbegin your exploration in the Mars Stu-dent Imaging Project.

The Inner Solar SystemCredit: Keith Watt


The Mars RaceOn October 4, 1957, the Soviet Unionlaunched Sputnik 1, the first man-made object into space. In doing so,they did more than launch a space-craft, they launched a race that wouldultimately end with the United Stateslanding a total of 12 astronauts on thesurface of the Moon. While manypeople are familiar with the MoonRace, not many people realize thatthere was a “Mars Race” as well. In1960, the Soviet Union attempted tolaunch two robotic space probes toMars. Both exploded at launch. In

1962, however,they successfullylaunched theirMars 1 probe andput it on coursefor the RedPlanet. Allseemed to be go-ing well until thespacecraft wasabout halfway toMars. Suddenly,all contact with

Chapter 2: Mars Exploration Background

As mentioned in Chapter 1, Mars has attracted the attention and imaginationsof observers for thousands of years. The first serious observations of the Mar-tian surface were conducted by Schiaparelli in 1877, whose work was expandedupon by Lowell in 1890. Until the dawn of the space age in the early 1960’s,telescopic observations were the only way we could study Mars. Even the besttelescopes, however, must still look up through the Earth’s atmosphere in orderto see out into space. It’s a lot like trying to watch clouds from the bottom of aswimming pool: the objects are there, but they are fuzzy, wavering, and hardto make out. If we want to conduct serious observations of another planet, weneed to go there.

the probe was lost. No one has everdetermined what happened to theprobe, but its loss gave the Americanteam another chance to be the first toMars.

Thrilled with the success of Mariner 2,the first unmanned mission to Venus,NASA began its program of Mars ex-ploration, hoping to be the first coun-try to explore Mars as well. Approxi-mately every two years the planets arein just the right position for an Earth-Mars trip that requires the leastamount of fuel. In 1964, NASA pre-pared to launch Mariner 3 and Mari-

SputnikCredit: NASA

Mariner 4Credit: NASA/JPL


ner 4 to Mars. During the launch ofMariner 3, the spacecraft’s protectivelaunch shroud collapsed, destroyingthe spacecraft. With only three weeksremaining in the low-fuel launch win-dow, NASA engineers scrambled to getMariner 4 ready to take the place ofits sister spacecraft. On November 28,1964, Mariner 4 launched successfullyand put onto the path to Mars. TheSoviet Union was not far behind, how-ever. Two days later, on November30, they launched Zond 2 and put iton course to Mars as well. There wasnow a literal race to the Red Planet.Two spacecraft were headed to Mars.Which would get there first?

The race stayed close for the firstmonths of the trip, but just as Zond 2reached the point near where Mars 1vanished, it too lost all communica-tions. NASA engineers joked about a“Great Galactic Ghoul” that ate Marsspacecraft. They stopped laughingwhen Mariner 4 began having commu-nications difficulties in the same area.Unlike Zond 2, however, Mariner 4 re-

solved its difficulties and sailed on toMars. On July 15, 1965, Mariner 4became the first spacecraft to visitMars. The spacecraft returned 21 im-ages that revealed the dry, crateredsurface of Mars. Dreams of a gardenplanet were laid to rest forever, butthe data showed that Mars was a fas-cinating planet in its own right.

Missions to Mars continued with Mari-ner 6 and Mariner 7 in 1969, both per-forming flyby missions similar to Mari-ner 4. Mariner 6 performed flawlessly,but Mariner 7, during its mission, sud-denly lost contact with Earth. Engi-neers were afraid the “ghoul” had re-turned, but they managed to re-es-tablish contact and determined that abattery on board had exploded duringthe pass behind the planet. The con-trollers instructed Mariner 7 to shutdown its damaged systems and con-tinue the mission. The two spacecrafttogether returned 58 pictures of theMartian surface taken from a distancehalf as far from the planet as Mariner4. The images, and particularly thosefrom Mariner 7’s flight over the Mar-tian polar caps, once again changedthe way we view Mars. Mariner 7 car-ried an infrared spectrometer on boardthat was able to analyze the composi-tion of the ice. The spacecraft discov-ered that the south polar cap of Marsis not water ice at all, but is insteadcomposed almost entirely of frozencarbon dioxide, or “dry ice”.

ZondCredit: Lunar and Planetary Institute


Mariner 9NASA engineers quickly realized thatin order to carefully study a planet,you have to not only go there, youhave to stay. What was needed was aspacecraft that would travel to Marsand place itself in orbit around theplanet. The United States was notalone in this assessment. The SovietUnion designed three spacecraft thatwould travel to Mars during the nextlaunch window. In 1971 they were tojoin the American Mariner 8 and Mari-ner 9 probes on the long journey tothe Red Planet. The Soviets, however,were attempting to leapfrog the UnitedStates: each of their spacecraft con-tained not only an orbiter, but also alander designed to descend and sendback the first pictures from the sur-face of Mars. The American Mariner 8spacecraft died when the second stageof its Atlas-Centaur booster rocketfailed to ignite. The Soviet Cosmos419 made it into space, but never leftEarth orbit because the ignition timerfor its last stage had been mistakenlyset for 1.5 years rather than 1.5 hours

after launch. The fleet of spacecraftheaded to Mars had been reduced fromfive to three in just a few weeks.

The three remaining craft, the SovietMars 2 and Mars 3 and the AmericanMariner 9, were all launched in May of1971. Once again, the race to Marswas on. The race was won by Mariner9, which was on a slightly faster coursethan its Soviet counterparts. On No-vember 14, 1971, Mariner 9 becamethe first artificial satellite of anotherplanet. Mars 2 arrived two weeks laterand Mars 3 shortly after that. Unfor-tunately, when the three spacecraft ar-rived at Mars, there was nothing muchto see. In September of 1971 a duststorm, visible from Earth, began whicheventually covered the entire planet.Nothing of this scale had ever beenobserved on any planetary body. TheSoviet Mars 2 dispatched its landeranyway, as it programmed to do, butthe lander crashed on the surface,sending back no data. Mars 3’s landerfaired a bit better, sending back a fewseconds of data before it was blownover and destroyed by the raging Mar-tian winds. Still, the Soviet Union hadbecome the first nation to land aspacecraft on another planet – even ifit didn’t do much once it got there.The Soviet orbiters snapped feature-less pictures of the dust-enshroudedplanet until their batteries died. Noth-ing could be seen through the dust onany of the images. Mariner 9, how-ever, had been designed with an on-board computer that could be repro-Mariner image of cratered area on Mars

Credit: NASA


grammed from Earth. NASA control-lers instructed the spacecraft to shutitself down and conserve power untilthe storm passed. By December of1971, the storm was over and NASAwoke up the sleeping spacecraft, whichreturned the highest resolution pic-tures of Mars that had ever been ob-tained.

Once again, new observations com-pletely changed everything we thoughtwe once knew. Observations of Marsby previous spacecraft had led us tobelieve the surface of Mars was acratered, dead landscape, not muchdifferent from Mercury or the Moon.All of those spacecraft, however, hadflown past only the southern hemi-sphere of Mars. The northern hemi-sphere of Mars is made up of smoothplains and lava basins, totally unlikethe cratered south. Mariner 9 alsosolved the mystery of the “seasonalvariations” Mars seems to display.These dark areas on the surface seemto change location with the seasonsand were thought to be indications ofplant life growing during the warmerMartian summers. Mariner 9 foundthat the dark areas were just hugeareas of dark rock exposed when thebright red Martian dust was blownaway by surface winds. As the sea-sons changed, so did the direction ofthe winds, uncovering new dark re-gions. The three previous Marinerspacecraft sent to Mars had shown noindication of volcanic activity. Mari-ner 9 discovered Olympus Mons, thelargest volcano in the Solar System,

and the three Tharsis Montes volca-noes, each larger than any volcano onEarth. The spacecraft also discoveredValles Marineris, the largest canyonsystem in the Solar System, formedwhen some cataclysmic event causedthe crust of Mars to bulge so much itcracked. The canyon is so huge, ifplaced on the Earth it would extendfrom San Francisco to Washington,D.C. The entire Grand Canyon wouldfit in one of its side canyons. Mostsignificantly, Mariner 9 discovered longchannels that look unmistakably likedry riverbeds – indicating that Marsmay have once had liquid water. Theseand other wonders were returned toEarth in the 7,329 images sent backto Earth during the course of Mariner9’s year-long mission. The spacecraftran out of fuel on October 27, 1972,and went forever silent.

The Viking MissionsNASA missed the next launch windowin 1973 because it was preparing foran even more ambitious mission: alarge-scale lander that would carry a

Viking orbiterCredit: NASA/JPL


complete laboratory to the surface ofMars. The Soviet Union was not idle,however, using the 1973 launch op-portunity to send four spacecraft to theRed Planet. None were successful. By1975, the American Viking 1 and Vi-king 2 spacecraft were launched andheaded to Mars. Like their Sovietcounterparts, each Viking spacecraftcarried both an orbiter and a lander.The landers carried no less than 14different experiments, most of whichwere designed to detect life on the sur-face. The trouble was that no two sci-entists agreed upon a definition of life,much less the means to test for it.Both landers touched down safely, Vi-king 1 on July 20, 1976, and Viking 2on September 3, 1976. The landersimmediately began the tests for lifethat were finally worked out as thebest that could be done. The experi-ments initially caused great excite-ment when they indicated they mighthave actually found biological activityin the Martian soil. Later analysis ofthe results, however, indicated that theexcitement was misplaced. Today,most scientists believe that the Viking

experiments did not in fact detect lifeon Mars. The question still remains,however: even if there is no life onMars now, did life ever exist there inits past? The question is still unan-swered.

With the end of the Apollo lunar pro-gram, NASA’s shrinking budget forcedit to concentrate on the Shuttle Trans-portation System, better known as theSpace Shuttle. As a result no Ameri-can spacecraft visited Mars for nearlytwenty years. The Soviet Union (whichwould simply become Russia the fol-lowing year) launched Phobos 1 and 2in 1988 to study the moons of Mars,but the “Great Galactic Ghoul” struckonce again: Phobos 1 was lost en routeto Mars just one month after launch.Phobos 2 arrived near Mars and man-aged to perform, among other things,important studies of the solar windnear Mars before a computer failurecaused controllers to lose contact withthe spacecraft just before reaching itsdestination. Neither mission wascounted as a success.

Viking landerCredit: NASA

Mockup of PhobosCredit: High Energy Astrophysics Science Archive Research Center


In 1992, the United States decided toreturn to the Red Planet and renew itsstudies of this fascinating world. Aswith the Russian spacecraft, Mars Ob-server lost contact with Earth a yearlater just as it was about to enter or-bit around Mars. The Mars Observermission cost nearly one billion dollars.It would be the last of the “old-style”planetary explorers.

Faster, Better, CheaperUnder the leadership of its new ad-ministrator, industrialist Dan Goldin,NASA decided to try a new approachdubbed “faster, better, cheaper”. Theidea was to use many, smaller space-craft, instead of one huge expensivespacecraft. In this way, the loss ofone craft would not doom an entireexploratory mission. The first in thisseries of “Discovery missions” wasMars Pathfinder. In contrast to thebillion-dollar Mars Observer mission,Pathfinder was designed, built andlaunched for only 250 million dollars,one-fourth the cost of Observer. LikeViking, Pathfinder included a lander,

but it also included something neverbefore attempted: an independentrover, named Sojourner, capable oftraveling up to ten meters (32 feet)away from the lander. The missiontested a number of new technologies.Instead of using a Viking-styleretrorocket, the Pathfinder lander wasencased in four large six-chamberedair bags. Upon entering the Martianatmosphere, the lander parachutedmost of the way to the surface, thendeployed and inflated its air bags forlanding. The spacecraft bounced 15to 20 times, sometimes as high as 50feet. The landing went exactly asplanned. On July 4, 1997, Pathfinderopened its landing petals, and beganits science mission while sending theSojourner rover on its way. The mis-sion was a complete success. Thelander returned over 16,500 images,some in 3D. The rover returned over550 images but, more importantly,sent back over 15 chemical analysesof rocks and soil, as well as data onMartian winds and weather. On Sep-tember 27, 1997, the Pathfinderlander, now called Sagan MemorialStation, failed to answer a routine sta-tus check. Controllers tried for sev-eral months to reach the silent craft,but finally gave up on March 10, 1998,officially ending one of the most suc-cessful Mars missions in history.

Although launched a month earlierthan Mars Pathfinder, an orbiter calledMars Global Surveyor actually arrivedat Mars after Pathfinder. Mars GlobalSurveyor was designed to use a tech-Pathfinder Lander and Rover

Credit: NASA/JPL


nique called “aerobraking”, in whichthe spacecraft dips into the Martian at-mosphere to slow down and place it-self in Mars orbit. Aerobraking is adelicate maneuver. If the spacecraftenters too low into the atmosphere, itwill burn up. The spacecraft spent al-most a year and half slowly modifyingits orbit around Mars until it was in anearly circular polar orbit. This orbitwould allow Global Surveyor to imagevirtually the entire planet during thecourse of its two-year science mission,which began in March of 1999. LikePathfinder, Global Surveyor has beena phenomenal success, returning moredata about the Martian surface and at-mosphere than all previous Mars mis-sions combined. The spacecraft car-ried not only a camera (the Mars Or-biter Camera, or MOC), it also carriedan infrared spectrometer (the ThermalEmission Spectrometer, or TES) de-signed to search for minerals and mea-sure the temperature of Mars, as wella laser altimeter (the Mars Orbiter La-ser Altimeter, or MOLA) which providedthe first accurate measurement of the

topography – terrain heights – of Mars.The spacecraft completed its primarymapping mission on January 31, 2001,but was in such good health, missionmanagers decided to extend the mis-sion and to continue gathering data.It was fortunate that they did so, ason June 15, 2001, Global Surveyorscientists detected the beginnings ofwhat would become the largest globaldust storm since the Mariner 9 mis-sion almost exactly thirty years prior.

Flush from the successes of Mars Path-finder and Global Surveyor, NASA com-missioned two more spacecraft for the1998-99 launch window. Mars ClimateOrbiter was to function as a Martianweather satellite and as a communi-cations relay satellite for the othercraft, Mars Polar Lander. Polar Landerwas to land near the south polar icecap of Mars and dig under the surfacein search of water ice. It also carriedtwo “penetrators”, called Deep Space2 (Deep Space 1 was a probe designedto study comets using an experimen-tal ion propulsion unit). Unfortunately,

Mars Global SurveyorCredit: NASA/JPL

Mars Polar LanderCredit: NASA/JPL


Climate Orbiter suffered from human-caused failure, similar to that whichstruck the Soviet Cosmos 419 in 1971.Navigation parameters were fed to thespacecraft in English units, when theprogram was designed to use metricunits. The spacecraft disappeared be-hind Mars on September 23, 1999, andnever reappeared. The fate of PolarLander is still unknown. The space-craft seemed to be functioning nor-mally as it entered the Martian atmo-sphere, but no signal from the surfacewas ever received. Theories includethat Polar Lander burned up on entry,crashed into the surface, or perhaps

it simply landed in rough terrain andwas unable to point its antenna atEarth. This last theory is particularlyironic: the spacecraft could have beencompletely healthy, it just neededsomeone to kick it back upright.Strangely, though, nothing was heardfrom the Deep Space 2 penetrators ei-ther, even though they were deployedearly in Polar Lander’s descent. Wemay never know what happened toMars Polar Lander – at least not untilwe are able to go there and look atthe crash site ourselves.

Mars Global Surface MapCredit: NASA


Similarities and DifferencesMars is similar to Earth in a number ofimportant ways. It has an axial tilt of23.98 degrees, very similiar to Earth’s23.44 degrees. Mars therefore hasseasons, just like Earth, with cold win-ters and warmer summers. Mars’ ro-tation period, its “day”, is 24 hours,37 minutes, again almost exactly thesame as Earth’s. Like Earth, Mars hasice caps at both poles. It has clouds,winds, weather, dust storms, volca-noes, and channels. For many years,Venus was considered the “twin” ofEarth. Unlike Mars, Venus is very simi-lar in size and mass as Earth andtherefore has very similar gravity. But

Chapter 3: Mars in the Solar System

Mars is a world of puzzles. It is both very similar to and very different from ourown Earth. Mars is the fourth planet from the Sun and orbits at a distance oneand a half times that of Earth’s orbit. As a result, Mars receives much less lightand heat from the Sun than the Earth does, so it is much colder. Also, unlikethe Earth, Mars has a very thin low-pressure atmosphere which is unable toretain what heat it does receive. Because of the temperatures and pressureson the Martian surface today, water cannot exist in liquid form. Mars today istherefore a dry, frozen desert.

Venus is a hothouse, with tempera-tures soaring to hundreds of degreescentigrade and atmospheric pressureshigh enough to crush our toughestmetals like tin cans. Mars, on the otherhand, could one day conceivably bechanged to be more like Earth throughadvanced engineering known as“terraforming”. In many respects,Mars is a much more hospitable envi-ronment than Venus, making it anobvious target for our imaginations.

But Mars is very different from Earthas well. Surface temperatures on Marsrange from hundreds of degrees cen-tigrade below zero in the winter tonearly freezing (0º C) in the summer.Because Earth’s orbit is nearly circu-lar, our seasons are virtually the samein both hemispheres. Mars travels ina more elliptical orbit around the Sunthan does the other planets, so it is20% closer to the Sun during south-ern summer than it is in northern sum-mer. This results in very long, rela-tively warm southern summers andvery long, cold northern winters. Marshas an atmospheric pressure less than

Earth/Mars ComparisonCredit: NASA/JPL


seven-tenths of one percent of Earth’s,far too low to sustain most forms oflife as we know it. The southern icecap is made mostly of frozen carbondioxide (“dry ice”), not water. Muchof the surface of Mars is covered withcraters much like the Moon. All ofthese differences make Mars a worldunto itself, rather than a “twin” of Earthor another planet.

The northern and southern hemi-spheres of Mars are very different. Ingeneral, the south is very heavilycratered, while the north is made upmainly of smooth dark plains. Thereare many exceptions to this generalrule, for example, Hellas Planitia(planitia are smooth, low plains or ba-sins) lies in the southern hemisphereand, at 3 km below “datum”, is thedeepest basin on Mars. The word “da-tum” is used rather than “sea level”,because, obviously, Mars currently hasno seas! The datum is defined as thealtitude at which the atmospheric pres-sure is 6.1 millibars (6.1 thousandthsof the sea level pressure on Earth).The planet isn’t spherical either. Thereis a very large bulge in the crust lo-cated at around 113º west longitude.This region, called the Tharsis Bulge,is home to the largest volcanoes onMars – and in the entire Solar Sys-tem. The southern hemisphere revealsthe ancient cratering record of impactsearly in the Solar System’s history. OnEarth, this record has been virtuallyerased by the effects of volcanoes,wind, and water. Planets such as Mer-cury died young, ceasing geological

activity not long after the period ofmajor impacts. Mars, however, wasgeologically active for most of the lifeof the Solar System – the great vol-cano Olympus Mons was probably ac-tive just thirty million years ago – sohas examples of young terrain in thenorth right alongside the ancientcratered terrain in the south. In manyways, Mars uniquely records the his-tory of the Solar System in its surfacefeatures.

Polar CapsThe polar caps of Mars change dra-matically over the course of a Martianyear (which is almost two Earth years).During each hemisphere’s winter, car-bon dioxide freezes out of the atmo-sphere at the poles to form “dry ice”.This dry ice causes the polar cap inthat hemisphere to grow by a substan-tial amount. As much as one-third ofthe atmosphere of Mars freezes intodry ice at each pole during winter inits hemisphere. Changes of this mag-nitude in the atmospheric pressure ofthe Earth would signal that a storm of

Mars South Polar Cap, Summer 2000Credit: Malin Space Science Systems


unprecedented power was forming,but on Mars it is just a part of theyearly cycle. In the summer, the tem-perature rises above the vapor pointof carbon dioxide and therefore the dryice sublimates back into the atmo-sphere. The polar cap then begins toshrink, though there is always someice left at the poles. The two polesare not the same, however. The icethat remains at the north pole duringthe northern hemisphere’s summer ismostly water ice, while the residual iceat the south pole is still mostly carbondioxide ice. Scientists assume thatthere is water ice buried below the dryice at the south pole. Mars PolarLander was intended to resolve thisparticular question once and for all(but unfortunately did not).

CratersAs with Earth and the Moon, Mars wasbombarded with debris left over fromthe formation of the Solar System.The craters left behind have many ofthe same properties as those on theMoon: a nearly circular raised rim,steep walls, and a smooth floor. If thedebris hit with enough energy to liq-uefy the surface at impact, a centralpeak often formed in the center of thecrater floor. Ejecta, material blastedinto the air from the impact, fell in ablanket that extends outward from thecrater. Unlike the Moon, however,ejecta blankets on Mars do not have aperfectly circular form. Many cratershave irregular ejecta blankets thatseem to indicate that some of theejecta flowed across the surface out-

side of the crater rather than simplyfalling straight back to the surface.Craters of this type are called rampartcraters because the ejecta is made upof sheets that have distinct outerridges, or ramparts.

Another unique type of crater on Marsis the pedestal crater. This type of cra-ter is found largely in the northernhemisphere. Craters of this type seemto sit upon a raised pedestal of ejecta.Some of these craters also show ridgeslike rampart craters, but in other casesthe ridges have been eroded away bywind. In some cases the pedestal cra-ter looks to be situated atop a flat,raised plateau which rises above thesurrounding terrain.

Any of these types, including the more“standard” lunar-type crater can bemade into an incomplete circle by lavaflows covering part of the rim. Theseflooded craters are particularly com-mon near the Tharsis Montes volca-noes.

Belz Crater, Chryse Planitia, MarsCredit: NASA


Wind FeaturesAlthough Mars has a very low atmo-spheric pressure, the surface winds arevery fast. Wind effects are respon-sible for many of the features that areseen on Mars today. Sand dunes, verysimilar to those seen on Earth, areabundant in the northern hemisphere.These dunes form in broad lines thatrun perpendicular to the wind direc-tion. By tracking these dunes, we gainsome idea of how the Martian windsflow over time. The wind is also re-sponsible for eroding the Martian land-scape, often in strange and bizarreshapes. The wind is strong enough toblow the red dust away to exposedarker-colored rock below, an effectwhich, as mentioned in Chapter 2,once convinced scientists that Marswas covered with vegetation.

VolcanoesMars has the largest volcanoes in theSolar System. One theory why this istrue is that Mars seems to have a muchthicker crust than Earth, and so itdoesn’t have floating, moving crustalplates. Instead of lots of compara-tively small eruptions, as occurs withvolcanoes on Earth, the pressure on

Mars built up into major eruptions thatalways occurred in the same places –the weak points in Mars’ stable crust.One of the most significant featuresinfluencing the development of volca-noes, however, is the Tharsis Montesbulge. The bulge is the site of OlympusMons, the largest volcano in the SolarSystem, as well as the three TharsisMontes volcanoes, each larger thanany volcano on Earth. Olympus Monsis 22 km (13.75 miles) high and 550km (343.75 miles) in diameter. Ifplaced on the surface of the Earth, itwould be two and a half times theheight of the tallest mountain on Earth(Mt. Everest at 8.85 km or 5.5 miles)and would cover almost the entirestate of Arizona! Numerous other vol-canoes dot the region as well. Thesevolcanoes were almost certainlyformed from lava upwelling throughvents in the fractures created by thebulge. No one really knows whatformed the bulge. A number of theo-ries have been proposed, but nonehave yet been proven. Mars has nomagnetic field to speak of, so it prob-ably has no molten, liquid core as theEarth does. Some rocks, however, doshow “frozen-in” magnetic field lines,which could be evidence that Mars hada strong magnetic field – and there-fore a liquid core – in the past. Whathappened to the core to cause it tosolidify? What formed the Tharsisbulge? These are some of the puzzlesthat Mars presents to us today.

Olympus MonsCredit: Goddard Space Flight Center


CanyonsCanyons exist in many places on Mars,but none are as famous as VallesMarineris (“The Valley of the Mariners”,named for the American probes sentto Mars). The largest canyon in theSolar System, Valles Marineris is evenvisible from Earth. The canyon is notactually a single canyon, but is insteada system of interconnecting canyons.Valles Marineris varies in depth, butreaches a maximum over 7 km (4.37miles). Individual canyons are asmuch as 200 km (125 miles) wide.The central section of Valles Marinerisis made up of three nearly parallel can-yons, having a total width of over 700km (437.5 miles) and nearly 2,400 km(1,500 miles) in length. The totallength of the Valles Marineris systemis over 4,000 km (2,500 miles). Thecanyon is divided into three generalparts. In addition to the central sec-tion, to the west, near the Tharsis Mon-tes, is an extremely complex systemof interlocking canyons called NoctisLabyrinthus. The eastern end of thecanyon is a region of chaotic terrainthat could be the result of huge floods

flowing out of the canyon after it wasformed. Unlike most canyons onEarth, Valles Marineris was not formedby flowing water. The canyon is an-

Central Valles MarinerisCredit: NASA

other effect ofthe Tharsisbulge. Onetheory is that itwas formed by aliteral rippingapart of the Mar-tian crust duringthe event thatcaused theTharsis bulge.Another theoryproposes that thecanyon wasformed whenmagma under-neath it wasdrawn out in the eruptions of theTharsis Montes. Once again, we havemany puzzles, but very few answers.

ChannelsAs mentioned previously, Mars todaycannot have liquid water present onits surface. We have ample evidence,however, that Mars did at one timehave water flowing across its surface.Much of this evidence is in the form ofchannels that appear to be the resultof water runoff and outflows fromflooding. We know some channelswere formed by flooding that resultedwhen large impact craters were formedon the surface. The force of the im-pact melted the permafrost (a layerof ice that scientists think lies frozen

Nanedi VallisCredit: Malin Space Science Systems


beneath the Martian surface) andcaused the resulting water to flow vio-lently away from the crater. This wa-ter eventually refroze or evaporatedinto the atmosphere. In addition towater-created channels, channelscould also have been formed by flow-ing lava. Channels formed by waterand channels formed by lava have verydifferent appearances. The character-istics of the channel (its walls, itsfloors, whether or not it has tributar-ies, etc.) also tell us something abouthow much water was present and howfast it was flowing. The questions ofwhat happened to the water on Marsand what the surface of Mars was likewhen water flowed across it are thecentral questions facing Mars scientiststoday. Our experience on Earth hasbeen that where there is water, thereis life. Is the same thing true on Mars?

AtmosphereThe atmosphere of Mars is very thin,but Mars still has weather! The atmo-sphere is composed of about 95% car-bon dioxide, 2.5% nitrogen, and 1.5%

argon. The remaining 1% is mostlyoxygen, carbon monoxide, and watervapor. We believe that much of thewater on Mars is frozen at the polesand under the ground in a layer called“permafrost”, but some of it actuallyexists as ice-crystal clouds that floatin the atmosphere. These clouds don’tlook like the fluffy cumulus clouds wesee here on Earth, but they can re-semble the thin, wispy cirrus cloudswe often see high in our atmosphere.Where different air masses come to-gether, cyclones can form on Mars, justas they do on Earth. The most strik-ing features of the Martian atmo-sphere, however, are the dust storms,which can grow strong enough to coverthe entire planet. In addition to thedust storm of 1971, which blockedMariner 9’s view of the planet, in 1977the Viking orbiters observed no fewerthan 25 major dust storms, two ofwhich grew to global proportions. In2001, the Mars Global Surveyor space-craft was fortunate to witness the for-mation and growth of the largest duststorm since the 1971 storm. We havelearned a great deal about how thesurface of Mars and its atmosphereinteract as a result of seasonal heat-ing. This is information that we canuse here on Earth as we try to under-stand our weather and its interactionswith the surface.

Local Dust Storm on the Surface of MarsCredit: NASA


OverviewThe surface of Mars has long beenthought to consist of a mixture of rock,soil and icy material. However, the ex-act composition of these materials islargely unknown. Odyssey will collectinfrared and visible images that willbe used to identify the mineralspresent in the soil and rocks on thesurface to study small-scale geologicprocesses and landing site character-istics. By measuring the amount ofhydrogen in the upper meter of soilacross the whole planet, the space-craft will help us understand how muchwater may be available for future ex-ploration. The spacecraft will addition-ally give us clues about the planet’sclimate history. Furthermore, the or-biter will collect data on the radiationenvironment to help assess potentialrisks to any future human explorers.Finally, the spacecraft can act as acommunications relay for future Marslanders.

Launch and InterplanetaryCruise InjectionOdyssey’s mission to Mars began at11:02 a.m. Eastern time on April 7,2001, as the spacecraft roared into

Chapter 4: The 2001 Mars Odyssey Spacecraft

(Note: Much of this material was taken from official NASA sources. The au-thor gratefully acknowledges their assistance!)

2001 Mars Odyssey is an orbiting spacecraft designed to determine the compo-sition of the planet’s surface, to detect water and shallow buried ice, and tostudy the radiation environment near Mars. The mission will last for at leasttwo Martian years, or almost four Earth years.

space onboard a Delta II rocketlaunched from Space Launch Complex17A at Cape Canaveral Air Station,Florida. Sixty-six seconds after liftoff,the first six solid rocket strap-ons werediscarded. The remaining strap-onrocket boosters were then ignited, andwhen their fuel was expended, werejettisoned. About 4 minutes, 23 sec-onds after liftoff, the first stage, thelower section of the Delta II booster,stopped firing and was discarded eightseconds later. About six seconds afterthat, the engine for the second stage

(the middle sec-tion of the Delta IIbooster) was ig-nited. The fairing,or nose-cone en-closure of thelaunch vehicle,was discarded 4minutes, 42 sec-onds after liftoff.The second-stageburn ended about10 minutes afterliftoff.

The Delta II rocketCredit: Boeing


At this point, the vehicle was in a low-Earth orbit at an altitude of 195 kilo-meters (120 miles). The vehiclecoasted for several minutes, and onceit was at the correct point in its orbit,the second stage was restarted for abrief second burn. For stability, smallrockets then fired to spin the thirdstage on a turntable attached to thesecond stage. The third stage sepa-rated and ignited its motor, sendingthe spacecraft out of Earth orbit. Af-ter the final burn, the third stage andthe attached spacecraft were despunso that the spacecraft could be sepa-rated and placed into its proper cruiseorientation. This was accomplished bya set of weights that were reeled outfrom the side of the spinning vehicleon flexible lines, much as spinning iceskaters slow themselves by extend-ing their arms. Approximately 30 min-utes after liftoff, the spacecraft sepa-rated from the Delta’s third stage, andthe remaining spin was removed us-ing the orbiter’s onboard thrusters.The solar array was deployed so thatthe Deep Space Network could acquire

the signal from the spacecraft. At11:55 a.m. Eastern time, flight con-trollers at NASA’s Jet Propulsion Labo-ratory received the first signal fromthe spacecraft through the Deep SpaceNetwork (DSN) station in Canberra,Australia, indicating that all was wellaboard the orbiter.

Interplanetary CruiseThe interplanetary cruise phase is theperiod of travel from the Earth to Marsand lasts about 200 days. It beginswith the first contact with DSN afterlaunch and extends until seven daysprior to arriving at Mars. Primary ac-tivities during the cruise include check-out of the spacecraft in its cruise con-figuration, check-out and monitoringof the spacecraft and the science in-struments, and navigation activitiesnecessary to determine and correctOdyssey’s flight path to Mars.

Odyssey’s flight path to Mars is calleda Type 1 trajectory, which takes thespacecraft less than 180 degreesaround the Sun. During the first twomonths of cruise, only the Deep SpaceNetwork station in Canberra was ca-pable of viewing the spacecraft. Latein May, California’s Goldstone stationwas able to view Odyssey, and by earlyJune, the Madrid station was also ableto track the spacecraft. The projectalso added the use of a tracking sta-tion in Santiago, Chile, to fill in track-ing coverage early in the mission.

The orbiter transmits to Earth usingits medium-gain antenna and receivesDSN antenna in Goldstone, CA

Credit: InterPlanetary Network and Information Systems Directorate


commands on its low-gain antennaduring the early portion of its flight.About 30 days after launch, the or-biter was commanded to receive andtransmit through its high-gain an-tenna. Cruise command sequences aregenerated and uplinked approximatelyonce every four weeks during one ofthe regularly scheduled Deep SpaceNetwork passes.

The spacecraft determines its orien-tation in space chiefly via a star cam-era and a device called an inertial mea-surement unit. The spacecraft flieswith its medium- or high-gain antennapointed toward the Earth at all times,while keeping the solar panels pointedtoward the Sun. The spacecraft’s ori-entation is controlled by reactionwheels (devices with spinning wheelssimilar to gyroscopes). These devicesare occasionally “desaturated,” mean-ing that their momentum is unloadedby firing the spacecraft’s thrusters.

During interplanetary cruise, Odysseywas scheduled to fire its thrusters a

total of five times to adjust its flightpath. The first of these trajectory cor-rection maneuvers (TCM) was sched-uled for eight days after launch, andit corrected launch injection errors andadjusted the Mars arrival aim point. Itwas followed by a second maneuver90 days after launch.

The remaining three trajectory correc-tion maneuvers were used to directthe spacecraft to the proper aim pointfor insertion into Mars orbit. These ma-neuvers were scheduled at 40 days be-fore arrival (September 14), sevendays before arrival (October 17) andseven hours before arrival (October24). The spacecraft communicatedwith Deep Space Network antennascontinuously for 24 hours around allof the trajectory correction maneu-vers. Maneuvers were conducted in a“turn-and-burn” mode, in which thespacecraft turned to the desired burnattitude and fired the thrusters. It wasnot Earth-pointed during the thrusterfiring, so no communication was ex-pected in this short but critical timeperiod.

Science instruments were powered on,tested and calibrated during cruise.The Thermal Emission Imaging Sys-tem (THEMIS) took a picture of theEarth/Moon system about 12 days af-ter launch confirming that THEMIS wasoperating normally. Star calibrationimaging was performed 45 days afterlaunch. Two calibration periods for thegamma ray spectrometer were con-ducted during cruise. Each of the2001 Orbiter Interplanetary Trajectory

Credit: NASA/JPL


spectrometer’s three sensors could beoperated during the calibration peri-ods depending upon spacecraft powercapabilities. The Mars Radiation Envi-ronment Experiment (MARIE) was de-signed to collect radiation data con-stantly during cruise to help determinewhat the radiation environment isthroughout the journey to Mars.

the upper part of the planet’s atmo-sphere. During each of its long, ellip-tical loops around Mars, the orbiterpassed through the upper layers of theatmosphere each time it made its clos-est approach to the planet. Frictionfrom the atmosphere on the space-craft and its wing-like solar arraycaused the spacecraft to lose some ofits momentum during each close ap-proach, known as “a drag pass.” Asthe spacecraft slowed during eachclose approach, the orbit graduallylowered and circularized.

Following aerobraking walk-out, the fi-nal stage of the aerobraking process,the orbiter was in an elliptical orbit witha periapsis (closest point) near a 120kilometer (75 mile) altitude and anapoapsis (furthest point) near the de-sired 400 kilometer (249 mile) alti-tude. Periapsis was near the equator.A maneuver to raise the periapsis wasperformed to achieve the final 400 ki-lometer (249 mile) circular science or-bit. The transition from aerobraking

Predicted Aerobraking orbitsCredit: NASA/JPL

Image of Earth taken by THEMISCredit: Arizona State University

Mars Orbit Insertion (MOI) andAerobrakingOdyssey arrived at Mars on October24, 2001 Universal Time (October 23in the United States). As it neared itsclosest point to the planet over thenorthern hemisphere, the spacecraftfired its 640-newton main engine for20 minutes, 19 seconds to allow itselfto be captured into an elliptical, orlooping, orbit around Mars. After cap-ture, Odyssey looped around theplanet every 18.5 hours.

Aerobraking is the transition from theinitial elliptical orbit to the two-hourcircular science orbit. It is a techniquethat slows the spacecraft down by us-ing frictional drag as it flies through


to the beginning of the science orbitrequired about one week. The high-gain antenna was deployed during thistime and the spacecraft and scienceinstruments were checked out.

Mapping Orbit and Communica-tions Relay PhasesThe science mission began in Febru-ary of 2002. The primary sciencephase will last for 917 Earth days. Thescience orbit inclination is 93.1 degreesor almost perpendicular to the Mar-tian equator. This is a nearly polar (90degree inclination) orbit, but the ac-tual poles themselves will not directlypass under the spacecraft. The orbitperiod will be just under two hours.Successive ground tracks (areas thatpass underneath the spacecraft) areseparated in longitude by approxi-mately 29.5 degrees and the entireground track nearly repeats every twosols, or Martian days of 24 hours, 37minutes.

During the science phase, THEMIS willtake multi-spectral thermal-infraredimages to make a global map of theminerals on the Martian surface, andwill also acquire visible images with aresolution of about 18 meters (59feet). The Gamma Ray Spectrometer(GRS) will take global measurementsduring all Martian seasons. The MarsRadiation Environment Experiment(MARIE) will be operated throughoutthe science phase to collect data onthe planet’s radiation environment.Opportunities for science collection willbe assigned depending on when con-

ditions are most favorable for specificinstruments.

The relay phase begins at the end ofthe primary science mission in approxi-mately two to five years. During thisphase, the orbiter will provide com-munication support for U.S. and inter-national landers and rovers.

Thermal Emission Imaging Sys-tem (THEMIS)By looking at the visible and infraredparts of the electromagnetic spectrum,THEMIS will determine the distributionof minerals on the surface of Mars andhelp understand how the mineralogyof the planet relates to the landforms.During the Martian day, the sun heatsthe surface. Surface minerals radiatethis heat back to space in characteris-tic ways that can be identified andmapped by THEMIS. At night, sinceTHEMIS maps heat, the imager willsearch for active thermal spots andmay discover “hot springs” on Mars.

In the infrared spectrum, the instru-ment uses ninespectral bandsto help detectminerals withinthe Martian ter-rain. Thesespectral bands,similar toranges of col-ors, serve asspectral “fin-gerprints” of

Thermal Emission Imaging System

Credit: Raytheon Santa Barbara Remote Sensing


particular types of geological materi-als. Minerals, such as carbonates, sili-cates, hydroxides, sulfates, hydrother-mal silica, oxides and phosphates, allshow up as different colors in the in-frared spectrum. This multi-spectralmethod allows researchers to detect,in particular, the presence of mineralsthat form in water and to understandthose minerals in their proper geologi-cal context.

Using visible imaging in five spectralbands, the instrument will also take20-meter (65.6-feet) resolution mea-surements of the surface to determinethe geological record of past liquid en-vironments. More than 15,000 images— each 18x18 kilometers (11x11miles) — will be acquired for Martiansurface studies. These more detaileddata sets will be used in conjunctionwith mineral maps to identify poten-tial landing sites for future Mars mis-sions. The part of the imaging sys-tem that takes pictures in the visiblelight will be able to show objects aboutthe size of a house. This resolution willhelp fill in the gap between large-scalegeological images from the Viking or-biters in the 1970s and the very high-resolution images from the currentlyorbiting Mars Global Surveyor. TheTHEMIS investigation is led by ArizonaState University in Tempe, AZ.

Gamma Ray Spectrometer (GRS)The Gamma Ray Spectrometer willmeasure the abundance and distribu-tion of about 20 primary elements ofthe periodic table, including silicon,

oxygen, iron, magnesium, potassium,aluminum, calcium, sulfur, and carbon.Knowing what elements are at or nearthe surface will give detailed informa-tion about how Mars has changed overtime. To determine the elementalmakeup of the Martian surface, theexperiment uses a gamma ray spec-trometer and two neutron detectors.When exposed to cosmic rays (chargedparticles in space that come from thestars, including our Sun), chemical el-ements in soils and rocks emit uniquelyidentifiable signatures of energy in theform of gamma rays. The Gamma RaySpectrometer looks at these signa-tures, or energies, coming from theelements present in the Martian soil.

By measuring gamma rays comingfrom the Martian surface, it is possibleto calculate how abundant various el-ements are and how they are distrib-uted around the planet’s surface.Gamma rays, emitted from atomicnuclei, show up as sharp emission lineson the instrument’s spectrum. Whilethe energy represented in these emis-sions determines which elements are

Gamma Ray SpectrometerCredit: University of Arizona


present, the intensity of the spectrumreveals the elements’ concentrations.

By measuring neutrons, it is possibleto calculate the abundance of hydro-gen on Mars, thus inferring the pres-ence of water. The neutron detectorsare sensitive to concentrations of hy-drogen in the upper meter of the sur-face. Like a virtual shovel “digginginto” the surface, the spectrometer willallow scientists to peer into this shal-low subsurface of Mars and measurethe amount of hydrogen that existsthere. Since hydrogen is most likelypresent in the form of water ice, thespectrometer will be able to measuredirectly the amount of permanentground ice and how it changes withthe seasons. GRS is led by the Uni-versity of Arizona in Tucson, AZ.

Mars Radiation EnvironmentExperiment (MARIE)Led by NASA’s Johnson Space Centerin Houston, TX, this science investi-gation is designed to characterize as-pects of the radiation environmentboth on the way to Mars and in theMartian orbit. Since space radiationpresents an extreme hazard to crewsof interplanetary missions, the experi-ment will attempt to predict antici-pated radiation doses that would beexperienced by future astronauts andhelp determine possible effects of ra-diation in the Martian environment onhuman beings.

Space radiation comes from cosmicrays emitted by our local star, the Sun,

and from stars beyond our solar sys-tem as well. Space radiation can trig-ger cancer and cause damage to thecentral nervous system. Similar instru-ments are flown on the Space Shuttlesand on the International Space Sta-tion (ISS), but none have ever flownoutside of Earth’s protective magneto-sphere, which blocks much of this ra-diation from reaching the surface ofour planet.

A spectrometer inside the MARIE in-strument will measure the energy fromthese sources. As the spacecraft or-bits Mars, the spectrometer sweepsthrough the sky and measures the ra-diation field. The instrument, with a68-degree field of view, is designed tocollect data continuously duringOdyssey’s cruise from Earth to Marsand while in Martian orbit.

Mars Radiation Environment ExperimentCredit: NASA/Johnson Space Center


Seeing the InvisibleTHEMIS is actually composed of twoinstruments, a thermal infrared (IR)camera and a visual (VIS) camera.You experience infrared radiation ev-ery day as heat! Each color that wesee in a rainbow actually correspondsto a specific wavelength or frequency.Red light has a very long wavelength,while blue light has a very short wave-length. Infrared light has wavelengthseven longer than red light – it’s a color“redder than red”, a color so red youreye can’t even see it! The range of allwavelengths, which includes the col-ors that your eye can see, is calledthe electromagnetic spectrum. Thepart of the electromagnetic spectrumthat your eye can see is actually a verytiny slice called the visible spectrum.The part of the spectrum that we callinfrared ranges from the edge of thevisible spectrum to the start of theradio portion of the spectrum. Yes,radio is nothing more than light! It’sjust a color of light so far beyond redthat your eye can’t perceive it. Withinthe visible spectrum there is actuallyan infinite number of colors, not justthe seven we usually give names to.The same is true of the infrared part

of the spectrum. The THEMIS IR cam-era has detectors sensitive to nine dif-ferent wavelengths, or “colors”, of in-frared light. Minerals on and just be-low the surface of Mars receive heatfrom the Sun and re-radiate that heatback into space. The re-radiated heat– infrared light – contains the “signa-ture”, composed of specific infrared“colors”, that allow THEMIS to detectdifferent minerals. By making mapsof the different colors received by theTHEMIS IR camera, we can map theminerals on the surface of Mars fromorbit.

Both the THEMIS IR and VIS cameras

First THEMIS imageCredit: Arizona State University

Chapter 5: An Introduction to THEMIS

Of the three instruments on board 2001 Mars Odyssey, the one you will beusing is the Thermal Emission Imaging System (THEMIS, pronounced THEE-mis). THEMIS is the second in a series of ASU instruments which are plannedfor the exploration of Mars. The first, the Thermal Emission Spectrometer, orTES, flew aboard Mars Global Surveyor. The third, a smaller version of TEScalled, appropriately enough, “Mini-TES”, will fly aboard the Mars ExplorationRovers (MER) in 2003. All use similar principles to explore the Red Planet.


are high-resolution. This means thatthey can see small details on the sur-face of the planet. Each “pixel”, ordot that makes up the image, on theIR camera represents an area of 100meters (328 feet) on each side. Thus,a football field imaged by THEMISwould take up just a bit more than one“dot” in the image. The VIS camera,on the other hand, can resolve fea-tures as small as 18 meters (65.6 feet)on a side. The VIS camera could there-fore see things as small as a house –which would appear as a single “dot”in the VIS image. Each VIS image isof a relatively small area, about 18 x18 km (11 x 11 miles), roughly thesize of a small town. The combina-tion of resolution and image sizemakes the VIS camera an excellentmapping tool. The Mars Student Im-aging Project will use the VIS camera.

Mission PlanningFlying a spacecraft to Mars cannot beaccomplished without a large staff tosupport it. In the case of Odyssey, thespacecraft itself is managed byLockeed Martin Astronautics (LMA) inDenver , CO, under contract to NASA’sJet Propulsion Laboratory (JPL) inPasadena, CA. Odyssey carries threescience instruments on board, each ofwhich is controlled by a separate team.Each team has its own needs for thespacecraft, and these often conflictwith other teams or with the needs ofthe LMA engineers. Within each in-strument team are several scienceteams, each with different priorities forobservations. In addition, orbital fac-

tors such as the position of the Sun orMars’ moons must be taken into ac-count. The mission planner is respon-sible for looking at the needs of all ofthese groups and trying to please ev-eryone! In reality this is often an im-possible task, but the mission plannertries very hard to make it all fit to-gether.

The Principle Investigator for THEMISis Dr. Philip Christensen. Dr.Christensen is responsible for the over-all management of the THEMIS projectand has the ultimate responsibility forthe instrument. Dr. Christensen de-cides what percentage of observationsavailable will be assigned to which sci-ence teams. That information is givento THEMIS Mission Planner KellyBender along with the requests for ob-servations from the different scienceteams. Ms. Bender takes these re-quests and schedules them as best aspossible so that Dr. Christensen’s per-centages are met and as many of thescience teams’ observations are madeas possible. She must also considerthe needs of the two other instrumentson board Odyssey, as well as the needsof the spacecraft engineers at LMA re-garding the positioning of the space-craft. It is not an easy task!

Once the mission planner has sched-uled all the observation requests forthe upcoming two-week period, shewrites a small program that transmitsthe commands to JPL. JPL “packages”the commands in a format that thespacecraft can read directly, then


passes that information on to LMA inDenver. LMA checks to make surethere are no commands that will harmthe spacecraft or other instruments,then passes the commands to theDeep Space Network (DSN), a systemof communication dishes spreadaround the world that maintain com-munication with Odyssey. DSN thentransmits the commands to the space-craft, which, if all was done correctly,carries out its new instructions. Oncethe observations are complete, Odys-sey transmits its data back to DSN onEarth and back through the pipelineto the mission planner. At this point,THEMIS Data Archivist Kim Murrayprocesses the data into a form that isusable by the science teams and handsthe new images over to them. In ad-dition to the two-week lead time re-quired for planning purposes, once the

commands are sent from ASU it cantake as much as a day before theytravel through the communicationspipeline and reach Odyssey. The ob-servations can usually be taken in aday, and the results are available onthe third day, if all goes well. Some-times problems with the spacecraft orwith the weather on Mars can delayobservations for as much as a weekor more. Exploring another planet isnever a routine job!

Teachers:It is important that you as the stu-dents’ MSIP teacher have a general un-derstanding of the spacecraft and itsmission, capabilities, and constraints,as this will help you guide your stu-dents to choose the most appropriatequestions for their research.

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