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OCR for page 66
OCR for page 67
3
Mars.
The Evolution of an Earth-like Planet
The first high-resolution images acquired of Mars by Me Mariner 4 spacecraft ~ the dawn of the space age
shadered popular notions of hears. Far from being ~ oasis' the surface of Mars appeared to be as battered md
barren as the Moon. With id Din Exosphere md bitter cold temperatures' Mars was more parched than the dried
places on Earth. The prosper ~~ life could have evoNed Here seemed dim.
Each subsequent mission to Mars has eh~ged that impression in surprising ways. Mariner ~ revealed
towering volcanoes' polar caps' md reheels apparently euthy water. Systematic observations of Be surface md
atmosphere by Viking led to ~ huge increase in our knowledge of the breads of martim geologic history md the
dummies of the current climax. We hi landed on Me surface for the firsttime. D~a from He recent Mars Globe
Surveyor (MOS)have again revolutionized our underbuying ofthe evolution oftheplmet(Figure 3.~'revealing
the importune of the very early development of Tharsis' discovering huge magnetic momalies from ~ early
magnetic field' md showing evidence for recent or even ongoing climate Tahoe. Fundamental information also
has been derived from the study of martim meteorites. Deviled analysis of these samples has invigorated the
debate over whether life ever arose on Mars.
Are we alone: is one of the most compelling questions in science. Is the development of life ~ common
occurrence or ~ event that is exceedingly rare: ~ Earth wherever wear exists in ~ liquid staid viable organisms
have been found. Mars is probably the most compelling pine to attempt to answer the question, Did life ever arise
elsewhere in He solar systems' because we know now that water once existed And under some eireums~ees may
exist today) in ~ liquid sate on the surface of Mars, md it likely exists in ~ liquid state ~ Kept in the crust. While
the pre-space-~ge vision of eiviliz~ions on Mars has been replaced with ~ more informed understanding through
exploration md discovery, Mars is still He most compelling md accessible target in He solar system on which to
Duress He question of lifers existence beyond Earth.
A synthesis of these discoveries md He results of scientific analyses show ~~' like Earth Mars is ~ planet of
contrasts. Both planets have had complex geologic histories md climates that evolved md edged; in both eases
FIC3UFtE 3. ~ (facing page; Da~ from the ~rs Orbiter Lear Altimeter MOLAR instrument on the ~rs Global Su - eyor
spacecraft have enable the conclusion of highly assure images of Marsh topography. Them two images show the 11~1
Planers two dissimilar faces. The northem hemisphere (upper fight is flat and lightly cratered. In Unhasty the muthem
hemisphere shows extremes of relief and is heavily cratered. Curlew of the MOLA ~m.
~7
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Is
HEW FR0~ IN =E 50~R HIM
liquid wear played art importers role in ~e evolution of ~e surface arid Oration of art environment hospitable to
life. Among ~e plar~ts' Mars is of particular ingress because of its similarity to Earth' yet the most importers
lessons to ~ learned Hem from the differences between ~e two ply. Mars science might most usefully be
thought of as ~ study of ~e evolution of art Earth-like ply.
UNIFYING THEMES FOR STINGIER OF MARS
The exploration of Mars has led us to the point of Ming able to understand the main elements or components
of its systems. The sum total of information from spacecraft arid telescope observations md from Earth-b~ed
research arid ar~alysis programs has led to ~ fairly complex first-order understar~ding of the ply: the composi-
tion md first-order dummies of its atmosphere' ~ broad understanding of its wear md climax history' its crusty
structure as inferred from global gravity arid topography' arid its surface arid crusty chemistry from remotely
sensed measurements arid ~e study of martiar~ memories. While the indiv idua1 component systems of Mars have
been illuminated' the relationships between Hem are less well underwood. Research addressing these crosmu~ing
questions or themes has ~e po~ntia1 to significar~tly advar~ our understanding of Mars as ~ ply. The themes
are as follows:
.
Mars as ~ po~nti~ abode of life;
Wa~r' atmosphere' md climax on Mars; md
Structure md evolution of Mars.
The first theme recognizes ~~ Mars has had in ~e past on its surface' md may continue to have today in id
subsurface' environments with all He ingredients needed to sustain life. Did life ever arise: md Does it exist
today: are importmt first-order questions. To answer these questions' however, we need to know more Bout
Mars md its evolution. If the answer to questions Bout life is yes, it will be impor~t to know where' how, md
for how long life evolved' md id relationship to the plmetts evolution. If the answer is no' Hen it will be equally
important to fry to understand why life did not arise. Clearly' He answer will be tied to He second theme' He
history of volatiles md evolution of He climax md He atmosphere. One way of addressing He question of life
will be by searching for ~ biological imprint on isotopic systems. But to use this type of approach will require
more complete understanding of the atmosphere' the climate md its history, md, of course, water.
Space exploration has taught us ~~ ~ strong coupling exists between the structure md evolution of planetary
interiors md their atmospheres md climates: that is, between the second md third themes. For example' He
discovery of localized, very strong remnant magnetism in its ancient crust suggest ~~ early Mars had ~ active
dynamo md ~ strong magnetic field. If this was He ease, it would have shielded He plmet from biologically
harmful solar And cosmic) radiation md inhibited the loss of vol~iles (w~er) to space.
One of He distinctive characteristics of Earn relative to other bodies in the solar system is the presence of life.
Over He past decade' we have begun to appreciate ~~ life on Earn has been more than ~ thin veneer of biology
passively enjoying He ride; in feet life has strongly influenced the evolution of Earn. Clearly Mars is not as
hiologieally active as Earn is, md it may even be inert. However' because Mars preserves part of id ancient
geologic record ~~ is now lost on Earth, md because it has ~ atmosphere, evidence for liquid water ~ some time
on its surface' md ~ ancient magnetic field, it provides ~ window into the early history of He evolution of
Earth-like planet md perhaps the origins of life.
MARS AS A POTENTIAL ABODE OF LIFE
Present Life
The surface of Mars today is cold' dry' chemically oxidizing, md exposed to ~ intense flux of solar ultraviolet
radiation. These four factors are likely to limit or even to prohibit life ~ or near He surface of the martim regoli~.
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Temperature is of ingress not only because of its controlling influence on microbial metabolic rams but also
because of its influence on ~e stability of liquid wear. Although ~e peak denims surface temperature near ~e
martiar~ equator cm rise above ~e freezing point of wear during much of the year, the average surfed ~mpera-
ture is about 220 K' well Plow ~e freezing point of wear. Liquid wear is essmlia1 for life as we know it. Wear
is abundar~t on Mars, but not in liquid form.) War vapor md ice crystals are premnt in the atmosphere, arid wear
ice is almost certainly present within ~e martim regolith ~ high latitudes arid ~ the surface in polar regions. At
increasing depth' where ~e rock is warmer as ~ result of the ply geothermal gradient liquid wear may be
presmt in pore spaces.2
To dew ~ single mt of robotic studies he searched for exam life on Mars: ~e Viking life-de~tion experiments'
which were desired to ~st for organisms ~~ used ~ Air carbon sours eider carbon dioxide or orchid molecules.
Though ~e result obtained by the Area sew of experiments are regarded as having shown ~e materials Id to
be devoid of both orgar~ic compounds md evidence of lift this in~rpre~tion has been subject to deba~.5
The lack of agreement highlights ~e difficulties inherent in ~e detection of viable microorganisms by robotic
mems. Indeed, even were there unanimity thy the Viking experiments did not show the presence of life' ~e
experiments could Fill be criticized as being overly ``geocentric,, in thy they showed ~ lack of evidence of
metabolism only of Hose types particularly common among ~rres~ia1 microbes' not of ~1 conceivable metabolisms
(nor even of various redox-reaction-~md microbial metabolisms well known on Early.
The problem of distinguishing between biological Id nonbiologica1 orchid compounds is also complicated.
The earbonweous ehondrites' interplme~ry dust particles' Id probably other bodies within the solar system
contain abundant organic material ~~ is s~uetur~ly similar to biological products. Definitive resolution of He
differences between biotic Id abiotie organic molecules requires highly sophisticated techniques well beyond my
that could be mmaged robotieally.
The accepted interpretation of result from He Viking landers is that He surface materials tested were devoid
of organic molecules Id of my other evidence of life.6 However' even without consideration of alternative
in~rpre~tions'7 the Viking results ergot be Eked as indicating thy life does not currently exist on Mars.
Organisms ~ the Viking sites might have been missed because He experimental conditions (em.' the nutrient
provided or processes followed) were not chosen correctly. Even more importantly' martim life might reside in
aqueous oases' such as my recently Utile volemie vend or fumaroles disks from He Viking lading sites' or
depths far beneath the surfeit regoli~ sampled by the Viking experiment.
Put Life
The surface environment of Mars may not always have been as hostile to life as it is today. Early in He
plmet~s history, He average temperature may have been warmer Id He Exosphere more dense, Id liquid water
may have existed ~ the surface. The geomorphologie evidence' especially valley networks, indicates that He
martim climate was wetter, warmer, Id appreciably more hospitable to life prior to about 3.S billion years ago
than it is ~ present. Fossil evidence of past martim life' if there was my' may be preserved in surface water-laid
deposit such as lake- or Embed sediments in evaporitie mineral p~s,3 Id in hydro~erm~ly deposited
mineral crush (Figures 3.2a Id by.
An imports zone that seems likely to have been habitable throughout martim history is the eru~1 sub-
surface, where wear may exist in ~ liquid ~ate. The geothermal gradient of Mars is probably such ~~ liquid
water is present ~ depths as shallow as 2 km near He equ~or.9 The discovery of Crest microbes living deep
within the Columbia [liver basely in He U.S. Pacific Northwest Id elsewhere on Earth' is ~ depths as grew as
3 km,~i is eonsis~nt win the possible presence of microbes living in similar settings on Mars. Samples from
hypothetical subsurface settings of life would be very difficult to access, yet such materials may have been
dislodged Id brought to He surface by meteoritic impacts.
A study of the martim (SNC) meteoric ALH84001 produced evidence suggestive of biological Utility on
Mars about 3.6 billion years Ho. This conclusion has not been widely accepted; the report has engendered much
discussion' bow pro Id eon, regarding each of He several intriguing indicators of life proposed.
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70
HEW FR0~ IN =E SOLAR MUM
FIGURE 3.~ An acria1 view of the Greg Prismatic Hot Spring in Wyoming5s Ycllowstone Nation Park. The color
variations are due to pigments in thermophyllic microns residing in the wears. Such ~~ms are Hug studied to unversed
the limits of life on Each ~d as possible clogs for environments where life may have exisM on Mars. Age Source of
louse Finley Island Park, Idaho.
FIGURE 3.2b Travertine deposits ~ the hlincrva Terrace, M~noth Hot Sprinted Ycllowstone Nation Park. Such deposits
are intimately asocial with microbial communities, aspects of which are commonly preserve in the kavertine ~posits.
Hot springs ~d their deposits are Wing studied to un~rs~nd the limits of life on Each ~d as possible Clogs for environ-
me~s where life may have exist on Mars. ~~e courtesy of lluss Finley, Island Parks Idaho.
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71
Environmental Context for Life
The question of life on Mars must trmmend ~ search for actual orgar~isms. It mud include ~e question of
whether the martiar~ environment is or ever was hospitable to ~e beginning of life. This is ~ broad md complex
questions arid ~e evidence may ~ so deeply buried in the past ~~ itcar~ be ar~swered only by gaining ~ extensive
arid deep knowledge of Mars. For example' on Earth e~me-driven metabolic procesms cm create char~ristic
biogenic isotopic signatures (affecting, in particular, ~e rages of compositions of ~e Cable isotopes of carbon'
sulfur, nitrogm, hydrogen, arid possibly iron). However' in order to use such isotopic measurements to ~st for ~e
past presence of life on Mars' we need to know ~e mope of abiotic fractionating processes there. The search for
life should be based on the premise thy to understar~d the po~ntia1 habitability of Mars, we must fully understand
the plar~et~s present arid past stales. We should be as prepared for ~ negative grower regarding Marcus po~tia1
habitability as for ~ positive one. The importar~ee of ~ positive mower is clear' but ~ neg~ive grower would
prompt inquiries into what the implications are for the plar~et~ differences between Earth arid Mars.
ELey Questions
(questions win po~ntia1 for ~ paradigm-altering discovery relend to the question of life on Mars include He
following:
Does life currently exist on Mars:
Did life ever exist Beret
A question win potential for ~ pivotal seientif~e discovery is-
How hospitable was md is Mars to life:
Future Dictions
The most important future activities with respect to the question of life on Mars are as follows:
I. Sample-return missions will be required to permit definitive lens in ~rrestria1 laboratories for present md
past life on hears (see section ``Priorities md llecommend~ions,, below); robotic missions preceding He sample-
return missions will assist in locating the most fruitful sites to be sampled.
2. A broad program of study of He Mars environment' present md past, is needed to understand the context
in which life did or did not arise on ~~ planet.
WATER, ATMOSPHE1tE' AND CLIMATE ON MAIM
Water
The topics that comprise He theme of whorl atmosphere, md climax on Mars are closely linked. As on Earth
water exists on Mars in mmy stabs md participates in ~ broad range of imports physical' chemical, md possible
hiologiea1 processes. Water has played ~ key role in the evolution of the martim climate md in the shaping of
Marks geological history.
The question of where wear is on Mars today is difficult to answer fully. We have direct observations of four
exposed martim wear reservoirs, which include water vapor in He a~osphere, water fee in the atmosphere'
seasonal water fee deposits ~ the surface' md permanent water fee deposits ~ the polar caps. Of He four' He
martim polar caps are by far the most massive. Recent MGS MOLA topographic profiles indie ate thy the mass
of water fee contained within Marks norm md soup polar caps' assuming ~ high iee-to-du~ ratio, is He equivalent
of ~ globe water layer 22 to 33 m thiek.~4
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79
HEW FR0~ IN =E 50~R HIM
Beyond the wear reservoirs the now cart be demand on Mars, bare is g God reason to suspect the presence of
hidden wear reservoirs whose combined muses should be much grower bars bosh of the reservoirs the are
currently exposed.~5 In Mares near-surface regolith, it is expected the wear is adsorbed on soil particles' arid
there is fragmentary evidence from the Viking Cas Exchmge experiment ~~ the mass fraction of the wear could
be on ~e order of ~ percent. Viking arid MOS observations have provided geomorphic evidence ~~ the layered
deposit surrounding the norm arid south polar caps also contain wear ice' but its mass fraction is currently not
well constrained. It is also expected ~~ near-surfa~ ground ice is to ~ found on Mars, as on Earth' arid
numerous geomorphologica1 indictors support this idea.) ~ Models predict the it should be present within the top
moors of the surface ~ latitudes as low as 20 degrees from ~e equator in favorable loc~ions.~7
Because of Marsha low surface temperatures, the partitioning of wear is heavily biamd toward its condensed
phases' causing ~e martiar~ atmosphere to be extremely dry arid ineffective ~ Sporing large quantities of
wear on seasonal time scales. Liquid wear on Mars is not expected to be sable on Mars today' because
temperatures exceed 273 K only ~ low latitudes during ~e warmest periods of ~e day' arid my liquid generated
would quickly evaporate arid be har~spor~d by the atmosphere to colder locations where it would then free=.
Some of the most exciting questions concerning Mars deal with the past distribution md behavior of wear.
Marty of them questions are motivated by geomorphic evidence such as runoff charmers' outflow charmers' arid
other features ~~ have been in~rpre~d to merry ~~ liquid wear may have been present periodically on ~e
surface of Mars in past epochs.~8 The recent MOS Mars Orbiter Camera arid Mars Orbital Lamr Altimeter
observations have provided evidence for large ch~els ~~ once flowed from ~e southern highlands to Me
nor~ern lowl~ds'i~ widespread mcient layering inferred by some to be of mdimm~ry origin,2° md small gullies
on order walls that are considered to be evidence for recent erosion by fluids (Figure 3.3~.~i
Atmosphere
Our knowledge of the composition of ~e Mars Ionosphere is band on measurements of minor gases such as
neon, krypton, md xenon md ratios of common isotopes in the ambient Exosphere 06Arp8Ar' i267~' i6Ofi7O'
i6Ofi8O, i4Nii5N, thigh) by ~e Viking descent mass spechome~r, ground-based md airborne spectroscopy, md
laboratory analysis of atmospheric gams captured in the vitreous components of martim memories. It is Nought
that ~ combination of impact erosion md longhorn atmospheric loss from ~e top of ~e atmosphere by solar-wind
sputtering md other processes' md possibly sequestration of COG md other gams in the crust of the plmet are
responsible for the present low Ionospheric pressure ~ the surface of Mars (the yearly average is ~6 mbar).
Marks present-day lower atmosphere is dominated by ~e behavior of CO2' wear vanor. md dub. as driven
~ O
AL ~ ~ . ,~ ,
by the h~rs~un eor~f~guration md by the interactions of CO~, water vapor' md dust win the surface. A
eombin~ion of the above. tweeter win issues of transport md cloud physics' eonstitu~s hears meteorology.
~easonai endues In me atmosphere mass of COG are up to 30 percent in He current epoch. Water vapor also
inches with clouds md surface marries; id average ~ua1 column abundance is ~10 to 40 preeipitable
microns of water ~ norm midlatitudes.
Very little is known about the upper Exosphere of Mars. However, He interactions between Marks upper
atmosphere md He impinging solar wind md solar ultraviolet light appear to have played ~ significant role in He
evolution of the martim atmosphere md in the transition from ~ warmer md wetter environment to He present-day
colder md drier environment. Only by understanding He processes that em occur in the upper atmosphere em we
fully understand what drove the echoes in He volatile inventory md in He climate md thereby understand He
evolution of habitability on Mars.
The only in situ measurement of atmospheric composition came from the Viking descent neuba1 mass
spee~ome~rs. These provided two midl~itude vertical profiles' in the altitude range of about 120 to 200 km, of
CO2, CO' N2, O2' md Ar densities during low-solar-activity conditions. Using the male heights Bus measured'
atmospheric temperature profiles were deduced. These temperatures showed quip large variations md averaged
c200 K. Some indirect md limited information on composition md temperatures has been obtained using airflow
md ionospheric information. The upper-atmospheric temperatures appear to vary by about IS0 K between solar
cycle minimum md maximum conditions. The z-axis accelerometer carried by the MOS provided ~ grew deal of
important information about total densities md temperatures during id extended aerobraking period.22
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73
FIGURE 3.3 The Mars Orbiter Emery on Mars Global Surveyor imaged the' channels in ~ Wrier in the region End
Gorgonum ~7.40 S. 168.00 W). Them features have En interpret by some researchers as Wing due to the ram flow of
wamr across the surfed. The numerous channels ~d apron deposits indigo ~t may Ens to hundre~ls of individual cvems
involving the flow of wear ~d Chris have occurred here. The channels ~d aprons have very crisps sharp reliefs ~d there are
no small impel craters on them, subduing 0t shed features are extremely young relative to the 4.5-hillion-y~r history of
Mars. The image is 2.3 km wide ~d illumination is from the upper left. Mars Global Surveyor, Mars Orbiter Camera.
libeled No. MOC2-241~ toured of NASA!JPL~lin Sped Scien~ Systems.
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74
HEW FR0~ IN =E 50~R DIM
The only in situ measurement of the thermal plasma composition, density' arid temperature in ~e ionosphere
of Mars were obtained by ~e retarding po~ntia1 ar~aly~rs carried Board ~e two Viking lar~ders' along win ~e
mass spectrometers mentioned above. Electron density altitude profiles were also obtained by several U.S. arid
Soviet spacecraft (~.g., Mariner 9~' using ~e radio occultation technique. Thus, we have some information on bow
the dayside arid near-~rminator-nigh~ide electron density values, covering the altitude rar~ge of about 120 to 300
km. No clear presence of art ionopause was seen in this database.
Cliche
Climax encompasses ~ broad range of complex interacting systems with ~ wide rar~ge of time scales. The
Mars climax system, which includes the surface' atmosphere' polar caps, arid accessible regions of the subsurface'
has undergone significar~t charge during ~e plus history. Three time scales of climb variability cm be
considered: in~r~ual' quasi-periodic' arid long term.
Multidecade telescopic records of grew dust storms, multiyear surface pressure records acquired ~ the Viking
larding sired multiyear orbiter observations of the appearar~e of ~e seasonal md residual polar caps, md large
Derisions in ahnospheric wear make it clear thy the climax of Mars exhibit distinct Derisions from one year to
the next (in~r~ua1 char~ges). Understanding the nature arid causes ofthese variations is importers for identifying
interactions among Me cycles of carbon dioxide, dust' arid wear in Marsh present climate.
Me of Me cornerstones of our understanding of the climax of Each is ~~ small, quasi-periodic variations in
Earthts orbital md axial elements over time males of lens to hundreds of thousands of years result in large-scale
chimes in Earths clim~e.~ Marks orbital md axial elements experience variability on time males that are
comparable to those of Earth' but Be magnitudes of these Derisions for Mars are signif~tly grea~r.24 The
consequent changes to the insolation ~ high latitudes undoubtedly have caused significant chimes in the seasonal
cyc les of carbon dioxide, water, md dust. Awed on our preset understanding' hears is the plum in Be solar system
that is likely to have experienced Be most signify quasi-periodic variations in its climate (Figure 3.4~.
A wide rude of surface features on Mars cm be interpreted as evidence for warmer climatic conditions
various times in Be plmetts history (longhorn climate change). There is general consensus that Mars possesses
all Be volatile ingredient necessary to produce ~ warm md wet climate, but the problem is that ~ Marks disuse
from Be Sun' the sable location for Marks volatiles is not in the atmosphere but in condensed phases, which
makes it difficult to maintain ~ stable martim greenhouse.25
Although Be earliest martim atmosphere was probably lost by impact erosion md hydrodynamic escape
during Be Early No~him era, ~ relatively robust atmosphere appears to have been reestablished during Be
No~him by primitive volatiles released during Be erection of the Tharsis Plateau by volemie md igneous
processes. The end of the No~ehim marked ~ huge eke in Be climax md probably in Be volatile inventory of
Mars. Erosion rams declined, valley network formation largely ceased' md magm~ism declined. The intrinsic
magnetic field appears to have declined or ceased ~ ~~ time; He loss of the protective magnetic field may have
allowed subst~tia1 solar-wind erosion of Be Ionospheres with ~ consequent eke in elimate.26
Key Qu~tiom
. .
Questions with po~tia1 for ~ paradigm-altering discovery related to whorl Ionospheres md climax on Mars
include He following:
What are the sources' sinks' md reservoirs of volatiles on Mars:
~ How does the atmosphere evolve over long time periods:
Questions with potential for ~ pivotal scientific discovery include the following:
Is there ~ active water cycle on Mars:
What are the dummies of the middle md upper Exosphere of the planets
What are the rates of atmospheric escape:
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75
FIGURE 3.4 The Mars Orbiter Emery on Mars Global Surveyor imaged the alternating layers of bright and dark mamria1
comprising the North Polar Cap. This image of one of the dark lanes crossing the cap reveals inferno layering. This layering
is thought to Tonsil of mixtures of wamr in and bush with the alto variations indicating different dun conventions in an
in matrix. The apparent regularity of the variations with depth may ~ indimlive of quasi-periodic variations in the martian
climam. The image (~.4~:0 N. 279.540 W) shows ~ region I. - km wide and the vertical relief from the top of the image to
the bonom is approximately 350 m. MOS MOLD M0002100~ Soured of NASA/JPL~lin Spew Scien~ Systems.
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76
HEW FR0~ IN =E 50~R HIM
A question whose crower would conbibu~ to building ~e foundation of knowledge of the solar system is-
~ ~ . - ~ ~ ~ ~ ~ ~ A ~ ~ A ~ ~ ~ A ~ ~
What is the thr=-dimensiona1 distribution of wear in the martiar~ crush
Future Di~iom
Importers directions for ~e future relating to Marsh whorl ahnosphere, md climax are the following:
I. The ground-leve1 chemical arid isotopic composition of the ahnosphere, including humidity, should be
tracked for ~ least ~ martim year ~ ~ network of trader stations.
2. The distribution of water (in both solid arid liquid form) in He crust' globally or ~ ~ wide varieW of sites'
should be established (e.g., by sounding radar).
3. The composition arid dummies of the middle arid upper atmosphere arid the ram of escape of molecules
from Be ahnosphere should be measured.
STItI}CTI~E AND EVOLUTION OF hIAl~
Structure and Aridity of Be Crust and Interior
Major advances in our understanding of the interior of hears have come recently in four impor~t areas:
. . .
~ The bulk composition of Mars is better constrained owing to ~ "really improved estimate of the moment of
'Hertz mane possible by Pathfinder measurements. The moment of inertia depends on He distribution of density
within ~ planet' md only ~ limited range of rock compositions have ~ given density.
~ Mars had ~ magnetic field in the past but Here is no present global field' ~ shown by high-amplitude
magnetic mom alies detected in the southern highlands of Mars by He Mars Global Surveyor.28
~ Crusta1 Slickness variations are fairly smooth across He dichotomy boundary between the northern md
southern hemispheres of Mars; thus, ~ impact origin for He low-lying northern hemisphere is not favored.29 The
crush thickness result are consistent with ~ plate tectonic hypothesis' but Hey do nof confirm that idea.
~ A key insight from the MOS topographic dam is ~~ the Tharsis Plateau predates He formation of
apparently fluvia1 reheels. This suggests ~~ the outpouring of 1~a to make the plateau may have released
enough carbon dioxide to form ~ insulating atmosphere md sufficient water to form the reheels md even
ocem.~°
Composition of the Crust and Interior
Most of what we know about the composition of Mars comes from Free lypes of measurement: If} in situ
analysis of He rocks md regolith by landers' At} orbital observations by emission md refiee~ee spectroscopy'
md (3) studies of meteorites ~~ are inferred to have come from Mars.
In situ Geyser by the Viking md Mars Pathfinder landers found rocks ~ the Pathfinder sin to be more
siliceous than the basaltic rocks ~ the Viking sins. The soil is similar ~ both sites md less siliceous than rocks
~ either. Measurements from He Thermal Emission Speebome~r aboard MOS extended these compositions
globally; mdesitie rock appears to dominate in He northern lowlands md basalt in the older southern highl~ds.32
Members of the SNG amatory of memories' comprising He shergodites, nakhli~s, md eh~signites' plus He
unique memorize ALH84~' are thought to have come from Mars. Five different rock types are known in He
SNG collection. They include basalts md lherzolites (shergo~ites), elinopyroxeni~s (nakhli~s)' ~ duni~
(Chassigny)' md ~ or~opyroxenite (ALH84~1). Most appear to be igneous eumul~es. None of these rocks
mashes He composition of the basaltic mdesites found ~ He Mars Ponder lading sib. Similarly' none
samples the surface-atmosphere interface, md Hey constitute ~ very inadequate sample of interior compositions.
OCR for page 81
i]
TABLE 3.l Comparison of Recommer~tior~s of Seier~ee Priorities win Experiments On Projected Flight Missions
Trlolu sion in Missions
Skiers Priorities
~ ~ 0 0 0
cs~ 0 0 0 0
~ O
~ 0 ~ ~ ~ ~
Parley Recommendir~g
00 0 ~ ~ ~ co
~ ~ ~ ~ ~ ~ ~ O
O
~ ~ ~ ~ ~ ~ ~ ~ ~ ° ~
~ v ~ ~ ~ ~ v
O ~ O O ~ O ~ O O
v v v v Z v ~ v v Z ~
:
:
NASA
Other
c~
O
csx ~ O (N
Z ~ ~ Z
IrJerior
Wh~ is the si~ md st~e of the core~
Is h4:~rs a~ive (irJerior :~ivity' tector~ics' voloar~ism)9
Wh~ is the thickr~e s~stru ~ure of the oru ~9
Wh~ i ~ the ~ otherm a1 gra die r~
Wh~ is the chara~eriorigir~Hvolutior~ of the ma~etic field~
Geochemisky ~d Petrology
Wh~ v~ri~ior~s of ~ochemistry ar~d petrolo~ are prese~9
Wh~ h:~e beer~ mechmisms of ~ochemic:~1 differer~iation
Is there evi~r~m for aqueous mir~eraliz~ior~9
Chrorlolo ~ ~d Str~igraphy
Wh~ are the relative ages of geologica1 units ar~d ever~ts~
Wh~ are the absolu~ a~s of ~ologica1 ur~its ~d everJ~9
Wh~ are the absolu~ a~s of orystalline rooks
Surfam Prooesses
Wh~ are the preser~t rates of erosior~ ar~d ~positior~9
Wh~ were the past r~s ar~d prooesses: w~er ar~d coli~9
Wh~ h:~s the role of impa~ or~ering beer~9
Wh~ role has voloar~ism pl~ed ir~ surface evolutior~9
Surfami~mosphere ir~teractior~: wh~ vol~ile sourm~sir~ks
W~er
Pre~ cycle: souroes' sir~ks' mechar~isms' d~amics~
Wh~ is the 3-D orusta1 wa~r distributiorVorigir~ (liquidlice)9
How has the hydrologica1 cycle opera~d ir~ the pa~9
Life
Does life exi~ or~ h4ars
Can ~ y chemic:~1 products of life be ~tected~
Do isotopic pahems suggest life
Wh~ o~ we leam from Artarotic meteorites
Atmosphere
Wh~ is the ourrer~ compositior~ of the atmosphere~
Wh~ are the ciroulatior~ d~amics o f the atmosphere (T, P)9
How has the atmosphere char~d over time
Wh~ is the radi~ior1 environmerrt at the surfam of h5ars
Wh~ is the r~:~ture of we:~ther or~ h4ars
Clim~e Cordrol
Wh~ is the ir~erarmua1 variatili~ of climate
Wh~ has beer~ the long-term clima~ history of the plar~et~
Upper Atmosphere ~d Plasma Er~viror~mer~
Wh~ are the d~amics of the upper atmosphere
Wh~ are the hot atom ~ur~d~ ~ s ~d e soape fluxes
Wh~ are the ior~ esoape fluxes~
Wh~ are the ma~etic field cor~figur:~tior~9
Wh~ are the proms~s cor~trollir~g the ionospheric ener~tics
o
00
o
O O O O
00 0
00 0
00 0
00 0
O O
O O O O O
O O
O O
O
00
o
o
o
o
O O O
o
o
o
o
o
o
O O O
o
o
O O
O
~ O ~
O O
00
00
O
O
NOTE: ~ the columr~ titled 1lP~1 Recommer~dir~g>~> solid ciroles i~r~ify the que~ions th~ eachpar~1 recommer~d for ~u~. The columr~
labeled 1lIr~olusion ir~ h~issions>> shows which missior~s will address these que~ions, solid ciroles si~ify missior~s th~ will cor~nka~ on e:~ch
scien~ obje~ive' ~d oper~ ciroles si~ify ~ les~r 1~1 of ~er~ion to th~ obje~ive. h~issior~s ir~ NASA>s h4ars Explor~ior~ Program are
li~ed sep~r:~ly from the missiorls proje~ed by other n~iorls. Dur~g the period wher1 this report was being prepared for public~iorl' the
Frerlch-led NetLm~r missior1 was omm1e d.
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dummies of ~e upper atmosphere of Mars arid rams of Ionospheric escape should be studied (among other
reasons) to constrain the rams of wear loss from Mars, ~ key factor in the vol~ile history.
In summary' ~e measurement objectives ~~ the Mars Parted has identified include ~e following:
~ Definitive measurements to ~st for the presence of extant or extinct life, or the geochemica1 arid organic
chemical evidence for past biological activity. These measurements will require highly sophi~ic^d equipment
procedures, arid sample proportion techniques not currently available' nor likely to be available in ~e foreseeable
future' for in situ experimmts. Consequently' samples relend from well-documen~ sins of promising biological
po~ntia1 mud ~ returned to Earth for detailed study.
~ Detailed charac~riz~ion of the geochemistry' mineralogy' trace elements' md chronology of samples
selected from well-documen~d locations md returned to Earth to address questions relevar~t to the absolute
chronology' climax arid wear history' igneous arid metamorphic evolution, arid weathering history of Mars.
~ ~~rmination of ~e sources, sinks, arid reservoirs of volatiles through inhered measurement of ~e
composition of ~e atmosphere (including humidity)' isotopes of atmospheric gases, md volatile coning of arid
processes in the subsurface' made over ~ least ~ martiar~ year, using long-lived gas Myers. Concurrent
measurement of the composition of He middle md upper abnosphere is required to provide ~ systematic under-
s~ding.
~ Determination of the sin of Marcus core, its current internal activity, arid id large-se~e plar~et~ structure
using passive seismometry ~ ~ minimum of four sites' operating for ~ lent ~ maim year.
~ Determination of the absolute chronology of Mars. Required are the measurement of ages of erys~lline
rocks from surfaces on ~ least four strategically chosen geologic units displaying conspicuously different crater
densities. This measurement objective em be achieved Trough sample return if appropriate surfaces are sampled'
mdior Trough in situ age de~rmin~ions made by landers if Be technology em be demoed to achieve
sufficient precision md accuracy.
~ Measurement from orbit of the dummies of the middle md upper Exosphere of Mars md the rate of
atmospheric escape.
~ Measurement of Me current neutral gas md ion escape fluxes; bow optical remote-sensing md in situ
instruments carried on ~ orbiter are required to achieve these objectives.
SiLGGESTED MISSIONS
Mars Idle Return
The Mars Panel attaches the greatest importance to Mars Sample lecture (MS1~' unquestionably ~ high-cost
mission. While MS1l e~of replace vermin crucial in situ measurements (em., hem flow' seismicity, eleetro-
magnetie sounding for whorl analyses of labile samples' md determination of atmospheric dynamics)' it is
seientif~eally compelling in id own right, md the ground-tru~ acquired from returned samples will aid Me
i~erpre~tion md greatly enhance the value of dam from orbital md robotic lander missions. Spaceport capabilities
that would eon~ibute to effectiveness in sampling include mobility in situ reco~aissmee mal~iea1 instrumenta-
tion' md ~ e ore drilling device. Cinder current conditions' it appears likely that living organisms' md more
generally all organic material' would be destroyed by oxidizing conditions in Me surface layer of hears. They may
be preserved only ~ depth in Me planet. Just what dep~entimeters, meters kilometers is urn own.)
Necessary capabilities include the ability to mmipula~ md document samples eollee~d md to package them in ~
way eonsis~nt win requirement placed by Me plme~ry protection protocol imposed on the mission. A radio-
isotope power system for He mission (see below) would expand the geographic range of sites that could be
sampled md would extend He missions stay time' allowing He collection of ~ larger md more carefully selected
suite of samples. Ample power undoubtedly will be important if drilling is eontempla~d.
It is essential ~~ the site to be sampled be carefully chosen, win He choice drawing upon He large body of
orbital md lander dam ~~ will be in place by He time He MS1l is flown. However, no single sample-return
mission will completely satisfy the need for this form of exploration, no mater how carefully it is plied. Mars
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Representative terms from entire chapter:
global surveyor
AS
is highly varied in its geology; prior to returning some martiar~ myriad to Earn it may be impossible for us to
underfed which type of sin has the higher po~ntia1 for providing samples ~~ contain evidence of life arid other
valuable scientific day; sample collection arid return represent ~ new endeavor, one thy may nof work perfectly
the first time. It will ~ necessary to plan for ~ series of MSRs over whatever spars of time the budget permits.
Mars Long-Lived Lander Network
The Mars Pme1 also recommends the emplacement of ~ network of long-lived surface stations on thy ply
~ modera~
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Mars Science Laboratory
The Mars Exploration Program (h~P) projects development of ~ Mars Science Laboratory (MSL)' presum-
ably ~ modera~-cost mission' for launch in 2009. Its instrument payload has teem stand only in ~e most general
terms. The mission may ~ imp ornery indeed essential' as ~ ~chnology-demons~tion precursor mission to MSR.
Mars Scout l\Ii~ions
The Mars Scout program tonsils of competed, Dimovery-class' principal-investig~or-led missions win
$300 million cost caps. The program was instituted by NASA to meet science goals arid opportunities not covered
by other missions arid to provide ~ mechar~ism for ~e hop to ~ responsive to discoveries. As structured' ~e
Scout program provides art excellent opportunity for NASA to accommodate science topics outside ~e principal
objectives of ~e h~P, arid for the broad science community to respond to discoveries md ~chnologica1 advar~-
meet. The Mars Parted strongly endorses NASA's desire to structure ~e Scout program after the successful
Discovery program. In thy regard, it is essential thy the measurement gods for the Mars Scout program be
direc~d toward ~e highest-priority science for Mars md be selected by peer review. As witnessed by the respond
to ~e recent call for Scout propose ideas (more thm 40 submissions were received), tremendous enthusiasm has
been stimulated by recent Mars discoveries for addressing scientific investigations not covered by ~e hop. Scout
provides for He MAP ~ component ~~ is highly flexible md responsive to discovery, md the panel recommends
that Scout missions be flown ~ every other Mars launch opportunity. Some of He mission priorities defined in this
chapter (e.g.' the ML3N md MAO missions) could be aceommod~ed in He Se out program as ~md-alone
missions or as target of opportunity on incarnations missions. The science priorities outlined in this chapter do
nof encompass the full range of science topics of grew importune to Mars ~~ may fit within the Scout funding
md mission profile. These are covered more completely in the - C report Assessmmt of Mars Sc~erzoe ~d
Meow pr~or~42 as well as in the recent report of He Mars Exploration Payload Assessment Group (MEPAC).43
IMPACT OF SAMPLE llETl}RN ON THE MARS EXPLORATION PllOGllAM
One of He major problems facing He MEP is choices. The abundance of new dam across all disciplines has
led to extraordinary discoveries about Mars that are being reported in rapid succession, md with He plied
program of NASA md intern~iona1 missions, this is likely to continue (see Table 3.~. The compelling nature of
the planet md this vigorous exploration program has spawned ~ deep md broad scientific eommunily whose
ingress md compelling questions span mmy orders of magnitude in space md time. Yet despite the apparent
richness of this exploration program, the resources for NASA's REP are nevertheless finis. The scientific
community md NASA are therefore faced with He critical question of prioritization.
Central to this debug is the question of sample return, on which there are two points of view. The firm view
is thy the costs of sample return will be high in terms of the spaceport resources md ir~frashueture needed to
handle' house, md analyze the samples. This investment will undoubtedly defer in situ md orbital investigations
of Mars during this effort. This view further advoea~s that because of this cost' sample return should be delayed
until such time as the science questions to be addressed by sample return are so compelling md He technology so
mature that success is assured. As the program moves forward then' the MEP resources should be directed toward
continued in situ md orbital investigations. For example, He current best estimates of the cost of sample return
rope between $~.S billion md $~.S billion' which would require NASA to combine the resources from two launch
opportunities to fit within the MEP cost profile.
It could be argued that for these same resources' four landed mienee packages win rovers could be sent to
some of the mmy interesting places on Hurst to conduct in situ surface science md life-detection experiments md
to establish well-ins~umen~d stations for interior' climate, md meteorology studies. This view that sample return
should be delayed is motioned in part by ~ fear ~~ if sample return is approached too quickly, Hen all Mars
Waldo kr~owr~ :~s the he ars Smart Leer or the Mobile Science Laboratory.
S5
science will be arrested to achieve this goal' md if ~e first samples are indistinguishable from SNG memories'
further support for Mars exploration will be jeopardized.
The contrary view is ~~ the mo ~ compelling question for Mars exploration' md one the is center to ~e SSE
Survey, is Are we alone9, arid ~~ only Trough the analysis of samples returned to Earn cart this question be
addressed to arty 1~1 of certainty. This view also holds thy the breads of Mars science to ~ addressed by ~e
upcoming missions (see Table 3.1~ is enormous arid will do much to provide ~e esmnti~ context to address this
question. However, the next leap in under~ar~ding Mars will only be achieved though the Physic of samples from
the surface underwood in ~ perry context. This view also holds ~~ ~e first sample return will neither address
all questions nor close the book on the life question. However' it will be critical for making the maximum use of
the huge investment in dam sew made over the preceding decade (such as shown by the lunar example). Sub-
sequent sample-return missions' interleaved win appropriate orbits md in situ exploration, will ultimately drive
exploration to the sins thy will maximize our under~ar~ding of Mars arid answer the question Are we cloned This
view is motivated in part by ~e sense ~~ sufficient information exists today to move toward the goal of sample
return arid thy ~e ~chnologica1 challenges are sufficiently large thy ~e program needs to main now in order to
achieve ~ launch early in the next decade (2013-2020), arid by ~ fear thy without ~ clear commitment to sample
return He hap will never achieve this goal arid will lose support.
The choice of which paw to take is not necessarily ~ either-or proposition. The true Gosh of sample return
are not yet known md will be refined over the next few years. Even with ~ high cost' Here will be abundant other
opportunities for Mars exploration. For example' following He flight of Mars Science Laboratory in 2009' He
next opportunities to fly to Mars are in 201~ md 2013. If He costs of ~ simple sample-return mission come in ~
the low end of the cost estimates ($~.S billion) md it is flown in the 2013 opportunity, then' amording to recent
reports of the hap budget to NEPAL, there should be sufficient resources to fly ~ competed Scout mission for He
2011 opportunity. If the Gosh for sample return are too high to bear for the 2013 opportunity this could be delayed
till the 2016 opportunity, md MS1l together with commend Se out missions in 2011 md 2013 would easily fit
within the current budget climax.
1lECOMMEN~ATIONS OF THE MARS PANEL TO THE STEERING GllOl}P
Mission Priorities
Mars Sample Deem
The Mars Panel Hushes the higher privily to missions ~~ will collect samples on Mars md return them to
Earth' bemiring ~ He 2011 opportunity if this is possible. Observations made by robotic orbiters md landers
beyond 2005 e~of alone answer the most impor~t questions regarding Mars: whether life ever started on that
plmet what the climate history of He planet was' md why hears evolved so differently from Earn. The definitive
answers to these questions will come from the study of hears samples' in the eons of orbital md surface in situ
measurement' of known provenance in laboratories on Earn.
~e Need for Sample Return ~e Search for Life. At our present sate of knowledge md ~ehnologiea1
expertise' md probably for the next sever al decades' it is unlikely ~~ robotic in situ exploration will prove capable
of demonsh~ing to ~ acceptable level of eer~inly whether there once was or is now life on hears. llesul~
obtained from my life-detection experiment carried out by robotic mems are likely to be ambiguous for these
reasons:
~ llesul~ interpreted as showing ~ absence of life will be challenged because He experiment that yielded
them were too geocentric or otherwise inappropriately limited;
~ llesul~ eonsis~nt with but not definitive of, the exis~nee of life (em., He deletion of organic compounds
of urn own, either biological or nonbiologie~, origin) will be regarded as incapable of providing ~ clear-cut
answer; md
AS
HEW FR0~ IN =E 50~R HIM
Result in~rpre~d as showing ~e existence of life will be regarded as necessarily suspect since Hey
might reflect the presence of earthly contaminants rawer Bars of art indigenous martiar~ biota.
Similarly frustrating result cart ~ expected in attempt to march robotically for either of the two categories
of fossil life thy might ~ preserved on hears: shomatoli~s arid microfossils. S~omatoli~s are accretions
org~osedimen~ry structures' commonly thinly layered' produced on Earth by the activities of mat-building
communities of mucilage-secreting microorgar~isms. Unfortunately, true s~omatoli~s on Earth cart be confused
with nonbiologically deposited look-alikes (~.g., in thin, sometimes wavy layers of mineral precipitates commonly
found in caves arid hot spring deposits on Earn; on hIars, such deposits may have ~m laid down, for ex ample' by
repeated wading md drying or framing arid thawing of mineral-charged salt Paris or shallow lagoons). If
shomatoli~-like structures were photographed on ~e surface of hIars, it seems vermin thy there would be
widespread uncertainty as to whether the objects demand were in fact produced by life. Similarly, it seems
unlikely thy robotic detection of objects resembling microfossils in or on the surfaces of rocks on hIars would
prove sufficiently convincing to demons to art acceptable 1~1 of certainty thy pad life existed on thy ply.
Me Ate ed for sample Ret'~r,~ C;eochem,~ry. In ~e area of geochemistry arid mineralogy, Win sections of
returned samples cart be prepared in ~rres~ia1 laboratories arid studied by microbeam techniques as well as
optically. Rocks contain ~ near-ir~'ni~ amount of information on ~ microscopic scale' some of it crucial to art
understanding of ~e rocks origin md history. flocks cm ~ disaggrega~d' md their constituent minerals cm be
studied chemically md isotopically. The dam obtained provide strong clues about md constraint on the nature of
the differentiation events that led to He formation of the rock. They also make possible ~ variety of approaches to
precisely dying igneous rocks in the sample collection. ~form~ion about the hIars climax will be found in the
layer of weathering products ~~ are expected to be found on rock samples. These products will almost certainly
be very complex minerals or amorphous reaction products that will tax the bed Ear~-based laboratory techniques
to understand. It is very unlikely ~~ fling but ~ highly qualitative md ambiguous description of the weltering
products could be made by robotic instruments operating on He martim surface.
Me kneed for Sample Return CI'm~e ~d Coupled Atmosphere-Surface-~tenor Processes. Some surface-
atmosphere md climax processes involving labile element or compounds must be studied in situ. Nevertheless'
the key measurements for understanding the relative loss of portions of the atmosphere to space md to surface
reservoirs are the compositions of surface minerals md Heir isotopic systemizes. Atmospherie-loss processes
(em.' hydrodynamic escape, sputtering) leave eharwleristie isotopic signatures in vermin element. Loss to space
versus to surface weltering (e.g., CO2 to carbonate minerals) is likely to produce isotopic fractionation in
different directions. The ratio of i5N to i4N in He maim atmosphere is underwood to have evolved over He past
3.8 billion years (it is currently I.6 times the Crest value), md ~ de~rmin~ion of this ratio in near-surface
materials may constrain the time of Heir formation. Compositional md isotopic analysis of surface minerals'
weathering rinds' md sedimentary deposits will establish He role of liquid wear md processes such as weathering
The corresponding measurement on volatiles released from near-surface materials are likely to be more heteroge-
neous md may provide fossils of past atmospheric md chemical conditions ~~ allow the past climate to be better
understood.
MA Meteorites No' ~ Substitute for Sample Return. The SNG meteorites do not obviate the need for
sample-return missions. SNG meteorites have provided ~ tantalizing view of ~ few maim rocks md ~ demonstra-
tion of how much em be learned when samples em be examined in Earth-based laboratories; however' Hey
represent ~ highly selected subset of martim materials, speeifie~ly' very coherent rocks of largely igneous origin
from ~ small number of urn own locations. Thus SNG memories are unhelpful in answering one of our
outstanding questions What is the absolute chronology of Hearst because although Hey em be accurately
dated He geologic units from which they are derived are up own. While returned samples are also ~ selected
subset of martim materials, Heir geolog ie context will be known' md they will be from sins selected because Hey
em provide particularly valuable information.
S7
Regarding ~e climax history of Mars arid possible life there' the samples the will provide ~e most informa-
tion are not igneous rocks' as the SNG memories are, but sediment arid soil samples. Taking Yosemite Valley as
~ ~rrestria1 ar~alog' ~e SNG memories represent ~e cliffs rather Bars ~e river muds md ~e sediment from ~e
outwash sheathing into Californians Entrap Alley. It is the lair materials the cart provide information about
chemical conditions, biological processes, arid timing; their martiar~ analogs, geologic features ~~ have ~e
properties of river arid lake deposits, will help most in understanding wear md life on the plmet.
Mars log- ~~r Network
The Mars Pared considers the ~e h~3N should ~ ~e mooed-priority Mars mission. The principal experi-
mend on Case landed stations should be passive seismometers arid maly~rs of ~e ground-leve1 atmosphere, bow
of which must continue to record dam for ~ least ~ year to achieve their potential. Earlier NASA advisory parcels
consistently recognized ~e imported of them experiments md recommended Heir implemen~tion.44
Seismic dam cart determine the sin of the core' which will constrain the bulk composition of ~e ply as
will information on the seismic velocities in the marble. Knowing the bulk composition of Mars is importers for
understanding the origin of the planets. Seismology cart tell us whiner the core is ~1 solid, all liquid' or part solid
arid part liquid (~ is Earths cores' which has ~ direct arid profound bearing on our understanding of plar~etary
dynamos arid Me present-day lack of ~ Mars global magnetic field.
In the area of martim atmospheric science' Mere are open questions of meteorology' atmospheric origin md
evolution, chemical stability, md atmospheric dummies. These questions are of particular interest for ~ broad
community of scientist' because useful comparisons with Each em be made ~~ may prove important for
understanding Me atmospheric evolution of both planets.
The Mars Panel mashes high priority to ~ better understanding of the martim atmospheric composition'
chemist' eireul~ion' md condensation of near-surf~e wear vapor as Me key components of climate systems
md for comparative studies of atmospheric dummies md evolution.
Mars tapper Atmosphere 0~r
The third privily of The panel is given to the Mars Upper Atmosphere Orbiter mission. The upper atmosphere
of hears drives the lower atmosphere in ~ variety of ways, md very little information is available on the martim
upper atmo sphere. There are no existing plans in The current U.S. hears Exploration Program to address my of the
seientif~e questions that are listed above concerning the upper atmosphere of hears (see the subsection <`Mars
lower Atmosohere Orbiter''i. I:~n~s Naomi ~d Neurons MPars Express will :~Mress these Questions to some
1 1
extent but much more dam will be needed to mem~giully clued these open Issues. Cow the Nozom' md Mars
Express will arrive ~ Mars during solar cycle minimum conditions' md dam from solar cycle maximum are
required in order to answer some of The outriding questions (e.g., nontherma1 escape).
l~nprionti~d Missions
Mars Sc~e,~ Ikoratory
The M8L mission may be important' indeed essential, as ~ teehnology-demonsh~ion precursor mission to
MS1~' but the panel saw little science for M8L thy ergot be done as well or better by the missions discussed
above. The deviled examination md analysis of rock samples em be done far more capably in terres~ia1
laboratories (though admittedly MSL could perform simpler analyses of ~ larger md more dispersed set of samples
than those that ~ MS1l mission could return). The ML3N mission could conduct much more comprehensive
atmospheric md seismic studies thm could M8L' which is ~ single mission' not ~ network. K-Ar ages remotely
measured by MSL, if this technique em be made to work' will provide only one dam point toward ealibr~ing the
martim geological column' with accuracy inferior to that obtained on MS1l samples in terrestrial laboratories.
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Since the parcels task was to prioritize science missions arid since it sees M8L largely as ~ ~chnology-
demonshation mission, it has not included MSL among the prioritized missions.
Mars Scout
The program of Mars Scout missions provides ~ excellent opportunity for NASA to accommodate science
topics outside ~e principal objectives of the Mars Exploration Program arid for the broad science community to
respond to discoveries arid ~chnologica1 advar~cement. If this activity is to be modeled after ~e successful
Discovery program' it is essential thy ~e science goals for Mars Scout missions ~ direc~d toward the highest-
priori~ science for Mars relend by peer review.
There is concern in ~e Mars science community thy Scout missions may be vulnerable to Ming sacrificed in
times of budget stringency. The parted urges thy ~e Mars Scout program ~ maintained win ~ high 1~1 of
protection.
Tedhnology Development
Sample return will not be ~ simple task, md it has not been achieved by ~ robotic mission over chart ~e
Russim sample return from the Moon 30 years ago. For the much more difficult sample return from Mars, marry
technologies will have to be developed' tested, md validated. Them include heard avoidance in ladings sample
selection' handling md delivery to the transfer chamber' Me Mars Ascent Vehicle' orbit rendezvous md capture'
transfer to Earth md quarantine on Earth. It will be ess~tia1 for precursor missions to MS1l to incorporate Me
teeing of essential technologies.
Sample return md ~ long-lived surface network will require sophisticated ins~umm~tion for science md
operations. While much Nought has been given to what sort of instruments might be required, Mere has been less
direct investment in Me development of instrument md demonstration of Me technology required for flight-
qualified systems.
An extremely important consideration in establishing Me capabilities of landed packages on Mars' static or
roving, is the power supply on which Hey rely Me options being solar panels md radioisotope power systems
(l?P8s). The Viking landers lasted as long as 7 years because Hey had UPS power. The twin ME1l 2003 rovers'
with solar panels, will operas for no longer than ~ estimated 90 days. This is because as He election of He Sun
echoes, He available solar power decreases; for the same reason, He rovers get colder md need more power to
keep warm. Meanwhile' dust is accumulating on the panels' furler reducing the power. The hi rovers are also
restricted by He needs of Heir solar panels to led in He 100 N to IS~ ~ latitude belt ~ relatively low elections.
The ML3N described above will not be able to operate within these constraints; m UPS will be essential. The
power problem will seriously affect sample-return missions as well. llelimee on solar power would mem that
samples will almost eerily have to be collected ~ low latitudes, which excludes those pans of Mars where
ground fee is stable md where over volatiles are mod likely to be present. If He sample-return mission has ~ rover
to collect samples' its lifetime will be short. The use of ~ drill to collect samples would require ~ generous supply
of power.
Data Any Ground-R=ed Oh~ervabons' and Lahoratory Studies
The Mars Exploration Program, with its missions ~ 2-year intervals' presents ~ new problem in fully exploit-
ing He amount md variety of dam ~~ will be collected. The volume md quality of dam returned by MOS alone
have been extraordinary, md He analysis of these day is only begir~E~ing. Win the rapid pace of Mars missions
plied for the next decade' the flood of dam em be expected to increase.
While the Mars Exploration Program consists of flight missions, exploration md understanding of the planet
as ~ system also depend on over modes of day acquisition. Some examples follow.
Te~cop`c studies
By
Continuing telescopic observation of Mars has played ~ key role in demonsh~ing ~~ the surfed of Mars
charges on ~ relatively short time scale (~ with seasonal charges, dust storms, evolution of the polar caps.)
Telescopic md spacecraft dam are highly synergistic, arid each plays ~ role in supporting the other. Support for
future robotic arid possible m~ed missions to Mars will require ~ long clim~ologica1 baseline. The long
baseline' partially obtained with ground-~md arid HST telescopic date will also con~ibu~ to art understanding of
the wear cycles between the atmosphere, regolith' arid polar caps, as well as spatially resolved dam on Jollily
cycles of whorl carbon dioxide' carbon monoxide, arid ozone.
oret`~l Bomb
Models are art essential component of arty scimlif`c endeavor. Examples of theoretical perry studies are
those ~~ crew ~e geod~amics of Mars, its interior structure' ahnospheric loss arid fractionation, arid global
climax arid general eireul~ion models.
Maroon ME
As already mentioned, the SNG category of martim meteorites plays ~ imports role in studies relating to
martim life md He plmet~s structure md evolution. Studies of this small group of meteorites in terres~ia1
laboratories have provided invaluable' if fragmentary, information about He geochemist md chronology of
Mars. NASA' the National Science Foundation' md He Smithsonian Institution have jointly supported ~ Antarctic
meteorite program since 1976, in which teams of expert search areas known to contain ~ concentration of
meteorites for ~ weeks every ausha1 summer; support of this program should continue.
Astrob~olog`~l ~~h
Studies of deep-sea hydrothermal environments hot springs, He deep subsurface' alkaline or acidic environ-
men~' md sea fee have revealed amazing microbial diversity in the form of uncultured organisms from environ-
men~1 extremes. Some of these habitats are po~tia1 malogues to past md present martim environment where
life may have arisen or might continue to exist. Through expanded knowledge Tout the po~ntia1 diversity of He
microbic world, we em explore how ancient microbial life might have impacted planets processes on Mars.
P=parabons on Earlb for Sample Return
A series of NASA md N1~C panels have considered the special problems assoeia~d with bringing samples
from Mars to Earth,45-49 md NASA has acknowledged He need to prevent forward md back eon~mination
every stage of the process of delivery. This includes He need to eons ~ quarantine facility to receive md
contain He samples.
A recent N1~C report drew at~tion to the long lead time required to prepare ~ hears Quarantine Facilily
(M0F) for the reception of Mars samples once they are delivered to Earth.~° Cal He basis of prior experience win
terrestrial biocontainment facilities md the Apollo Lunar lleeeiving Laboratory, He authoring eommi~ee estimated
that 7 years would be required to design, eons~uet, md staff the M0F. To this must be added the time needed to
clear ~ environmental impact statement md to carry out several N1~C recommendations for recormaissmee
studies that are needed to inform the design md operation of He M0F.5 ~ The aggregate of time required will strain
the schedule even of ~ 2011 launch (2014 return). It is impor~t ~~ scientific research md design studies that
mud precede the design md eons~uetion of ~ Mars Quarantine Facility begin immediately, md design md
eonshuetion of the facilily should begin ~ He earliest possible time.
Looo!
To
HEW FR0~ IN =E SOLAR MOM
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39. See' for example' Up: Studies Board' National Re~:~rch Councils An of Mare Scte~e a~ Mt~`o~ Prtorttt~> National
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40. See' for ~ xample' hears Explor~ior~ Payload Assessmerd Group (h] EPAG), 11h4ars Explor~ior~ Program: Scier~ific Goals' Oboe Fives'
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41. See' for example' Span Studies Board' National Research Cour~cil' AD of Mare She FEZ M~`o~ Prior National
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42. Span Studies Poard' National Research Council, AD of Mare Scow an Manor Prior N:~tior~al Academies Press'
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43. hears Explor~ior~ Payload As~ssme~ Group (h4EPAG] shears Explor~ior~ Program Sciertific Goals' Objectives' ~~estig~ior~'
Ad Priorities>~' Demmber 2000> irk Poor Explore Mary JPL 0 ~ -7> Jet Propulsion L~or~ory' Par Calif.> 2001.
Art. Span Studies Poard' National Research Council' AD of Mars Scow a~ Manor Priorly National Academies Press'
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Ames Research Cerder' Coffee Field' Calif.> 2000.
~ . hears Sample H~dlir~g Ad Requiremer~s Pan l (UNSHARP) ~ F`~l Report' NASAfTh] -1?~-209145' Jet Propu lotion Laboratory'
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49. Span Studies ~ card' National Research Councils Awry a~ Cerh4~ho~ of Marha~ Samples, N~ior~:~l Academy Press' Wash-
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50. Span Studies ~ card' National Research Councils Brat a~ C:erEficado~ of Marha~ Sampler' National Academy Press' Wash-
ir~or~' D.~.> 2002.
~ ~ . Span Studies ~ card' National Research Councils Awry a~ Cerhbcado~ of Marha~ Samples' N~ior~:~l Academy Press' Wash-
ir~or~' D.~.' 20 02.
