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New Frontiers in the Solar System: An Integrated Exploration Strategy (2003)

Chapter: 1 Primitive Bodies: Building Blocks of the Solar System

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Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
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Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
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Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 15
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 16
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 17
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 18
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 19
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 20
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 21
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 22
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 23
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 24
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 25
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 26
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 27
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 28
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 29
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 30
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 31
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 32
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 33
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 34
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 35
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 36
Suggested Citation:"1 Primitive Bodies: Building Blocks of the Solar System." National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. Washington, DC: The National Academies Press. doi: 10.17226/10432.
×
Page 37

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1 Primitive Bodies. Builcling Blocks of the Solar System The solar systems primitive bodies are those objects ~~ have undergone ~ low degree of chemical md physical ~ter~ion since Weir eondens~ion md aggregation from the solid md gaseous materials in the solar nebula some 4.6 billion years ago. These bodies are primarily smut (less than ~ few hundred kilometers in size) md are found mostly in the vast region beyond the orbit of hours. The primitive bodies And materials) include asteroids' comes' small plme~ry Bellies' the objects in the Kuiper Belt md He Oort cloud' Triton, Pluto' md Charon, md interplme~ry dust (Figure 1.~. While in the strictest sense ``primitive'' mems eddy unehm~ed' the definition is flexible in plme~ry science md is used in ~ relative sense both in the research community md particularly in this report. All of these objects md materials have experienced some hewing in the form of energy from Be Sun md the deeply of incorporated radioactive element. Moreover, hem from collisions md tidy dissipation has caused some degree of eke on the surface md in the interiors of mmy primitive bodies. Over factors affecting Be surfaces md near subsurfaces of bodies without atmospheres include ultraviolet solar radiation, the solar wind' cosmic rays' md trapped particles in planetary environments. Billions of years of bombardment by high-velocity meteoroids of every size (micrometers to kilometers) have affected every known surface in He solar system' causing physical md chemical ehm~es ~ the exposed surface md erecting soils md pulverized subsurface regions (regoli~) by severe meehmie~ fraeture.i Hem generated inside larger bodies has caused Hem to segregate He heavier materials (metals) from the lighter marries (rock md ice) in ~ process of differentiation. The easily evaporated materials (vol~iles) have been partly lost from some small bodies by either internal or ex~rna1 heating md escape into space. From He plmet~ science perspective, therefore, <<primitive,, mems "substantially unaltered,"' primarily from ~ chemical point of view, even though some interns mewing md differentiation may have occurred. Aster- oids md domed are primitive, but the terrestrial md gist planets are not. The distinction is gray when highly differentiated asteroids, large planets satellites' md Pluto are considered (although Pluto~s bulk composition is FIGURE I.1 ~facz~g paged A montage of spacecraft Ages of ~ small sub's of ~e solar Ammo primitive Alias. ~~- w~se from rawer nght ~3 Anthill, the nucleus of Comet I9P~orrelly~ the martian moons Deimos ~d Phobos, 433 Eros 243 Ida ~d 951 Oaspra. Toured of Poor Thomas, Comell Universiky.

~4 HEW FR0~ IN =E 50~R HIM almost certainly primitive). Object excluded from this view of primitive bodies are all ~e major ply ~e Moon' arid the large sullies of Jupiter, Saturn' arid Urar~us. UNIFYING THEMES FOR STUDIES OF PRIMITIVE BODIES The ply originated from the accretion of solid arid gaseous myriad in the solar nebula.2 The first bodies to form in ~e nebula were millimeter- to kilome~r-si~d plar~simals.~ Marty were subsumed into ~e ply arid Heir large sa~lli~s, but others remained behind arid are known today as primitive bodies. Most of the object considered primitive have not bun sub~ar~tially hewed or otherwise charmed in ~ chemical or physical sense since they formed' but others (~.~., certain asteroids arid comets' Triton' Pluto, arid Charon) have been hewed to eying degrees.~~5 Several populations of Base primitive bodies remain in different regions of the solar system' notably the aneroid belt the Kuiper Belt arid the Oort cloudy Some mem~rs of ~~e groupings have left their naive regions through gravit~iona1 mixing; indeed' objects ~~ originally formed in the outer ply - region arid thy were then expelled toward Heir current region by the gravitations action of ~e girt plays probably populated the entire Oort cloud. Life on Earth is Bought to be ~ product of the confluence of the necessary materials arid art event of origin. The neatest marries include liquid water, carbon-bearing molecules' arid energy, all of which were present on early Earth. Life arose early in our plar~et~s history. One widely held view is ~~ life arose ~ lent 3.S billion years ago, md perhaps as much ~ 3.8 billion years but He origin event or events remain urn own md the en act timing is uneer~in.7 Organic molecular myriad carrying complex assemblages of carbon, hydrogen, oxygen' md nitrogen was delivered to the sterile early Earth by comets md asteroids' md some may also have been formed by impact events in the early ocem md atmosphere.8 Complex organic material exists in interstellar dust in our galaxy md others md Bus predates He Sun md plme~.~° However, as researchers survey the primitive bodies md plme~ of the solar system' they find compelling evidence not only of the preservation of ancient organic mater but also of He formation md destrue- tion of organic molecules in modern environment. Wa~r' too' is common boy in interstellar space md through- out He solar system, Bough its presence in He liquid phase depends on special eireumstmees of temperature md pressure. ~ several eases, however' even where water is not now ~ liquid, Here is evidence ~~ the liquid phase once existed. Thus, ~ search for organic muter in the solar system is ~ exploration of He range of environment in which life may have originated md ~ search for ~ understanding of our own origins as well. Two clear themes therefore emerge as basic to study of the primitive bodies of the solar system: Primitive bodies ~ building blocks of the solar system' md ~ The origins of organic mater that led to life on ~ least one planet. The next two major sections expand upon these themes. PRIMITIVE RODIES AS RLILDI1~G BLOCKS OF THE SOLAR SYSTEM Fun~nen~l Issues The fundamental questions concerning primitive bodies as building blocks of the solar system em be summa- rized as follows: . ~ Where in He solar system are the primitive bodies found, md what rude of sizes' compositions, md other physical characteristics do they represent: What processes led to the formation of these objects: efirlitions of te~ica1 Arms ~d acrorlyms not ~ xplairled ir1 the text cm be found ir1 the gloomy in Appendix E.

pRIM~E BODIES Since their formation, what processes have Blared ~e primitive bodices How did primitive bodies make ply How have they affected ~e pits since the epoch of formation: ~5 Primitive bodies are highly varied in sing surface properties, composition, arid probably origin. Apart from in~rplm~ary dusk ~~e bodies rar~ge in sin from ~ few lens of Myers to 2~SW km (Pluto arid Triton). Some are snowy which while others are charcoal black. Some have igneous arid over minerals on their surfaces, while others have ices, md still others have combinations of ice arid rock. Simple arid complex orgar~ic chemicals are plentiful. The asteroids have highly varied compositions, win combinations of rock, metal' arid organic com- pounds, while domed contain the same materials in ~ matrix of ices of various compositions.) ~ Some asteroids have men thoroughly melody while others have not. Some domed have men externally heated, with consequent char~ges in intema1 structure' but others appear to have been entirely uncharged since Hey formed. In~rplar~e~ry dust near Each appears to come from both comets arid asteroids' arid it contains minerals arid organic solid ma. Triton' Pluto' Charon' arid probably several large Kuiper Belt objee~ have icy surfaces arid have probably been heated sufficiently for Heir interiors to differentiated Pluto arid Triton have signif~ear~t Ionospheres. Triton is geologically active; Pluto arid over bodies in this region of the solar system may also be active' md volatile trar~sport clearly takes places on bodies such as Triton arid Pluto. Their surfaces record their bombardment histories' hence the eollisiona1 history of He Kuiper Belt popul~ion.~4 I - Brat C~`ons Questions thy emerge from eonsider~ion of primitive bodies as building blocks of He solar system include the following: Are Here Pluto-size md larger bodies beyond Neptune: How do the compositions of Pluto-Charon md Triton relate to those of Kuiper Belt objects What are the basie physical properties (mass' density' size) of Kuiper Belt objects' Centaurs, md comet ~ What are the interior properties of all these bodies, md how do Hey differ from the surface compositions md properties: Are Hey differentiated: What are the surface properties md compositions of these bodies' md how do endogenous md exogenous processes affect them: Do Pluto mdior large Kuiper Belt objects show interns aetivi~, as Triton does: What are the compositions of comet nuclei' md how do they relay to Kuiper Belt objects: ~ What is the origin of He organic mater in carbonaceous meteorite parent bodies, md what are the parent bodies of the mmy different types: What organic materials occur in primitive bodies ~ various heliocentric distances: What is the origin of hydrated miner~s in He meteoric parent bodies' md what do fluid inclusions in meteorites tell us about conditions in the solar nebula md parent bodies: What is the origin of mierome~ori~s: What are the albedo md color sties of Centaurs, Kuiper Belt objects, md comet These questions are addressed md spelled out in more deviled questions in He remainder of this Shapiro Future D`~`ons A mission to Pluto-Charon md He Kuiper Belt em give critical' entirely new information on the physical properties of Pluto-Charon md members of the trms-Neptunim population. Despite Heir limitations relative to flight missions' additional Earth-based remo~-sensing observations will give crucial new information on He compositions md over physical properties of primitive bodies in various populations. Such work requires He

HEW FR0~ IN =E 50~R HIM availability of the largest telescopes arid mod mourn inshumen~tion. Radar observations of object near Earn are critical to studying certain classes of asteroids arid comet. The improvement of laboratory techniques for ~e ar~alysis of perry materials (memories arid returned samples) offers the promise of new information arid new perspectives on materials returned from primitive bodies. Spacecraft encounters win comet arid asteroids will continue to expired our perspectives on ~e overall nature arid variety of Base objects, but there is art urgent need for samples collected from known sins on well~harac~ri~d objects to be returned to Earth for analysis. Cur~ion arid Cysts of these materials are essential. The Variety and Distribution of Primitive Belies in the Solar System More chart 40~000 numbered asteroids are known, mostly orbiting the Sun between hears arid Jupiter but win ~ significant population in elliptical orbits thy cross ~e paws of the inner plar~ts' Mercury Trough Mars. Most of ~e asteroids decreed in the zone between Mars arid Jupiter arid occupy Table orbits' but some object thy are called asteroids Perhaps ~ perched are former homed thy originated elsewhere arid are no longer wlive.~5 An urn own fraction of ~e asteroids are binaries, consisting of two Spared objects orbiting ~ common center of gravity. Most of Me meteorites thy fall to Earth are fragments from collisions among the asteroids. The varieW of meteoric types shows ~~ there are marry different kinds of as~roids.~6 All four gimt plar~ets (Jupiter through Neptune) have families of distmt small satellites thy have Me appearance md other characteristics of asteroids; these are presumed to have originated elsewhere in We solar system md to have been captured subsequently by the gravi~ fields of the plme~. The ironer, small satellites of the gist planets are also considered primitive bodies' although Hey may have originated in He vicinity of their parent planet ~ part of the plmet-forming process. Two vastpopul~ions of primitive bodies exist beyond Neptune' bow predicted from He orbital eharae~risties of comets; one of these is now He subject of vigorous exploration. Comets with periods greater than 200 years md with random orbital inelin~ions, of which I'200 have been observed in the lasttwo millers originate in He Oort cloud, ~ collection of more than ~ trillion icy bodies that orbit the Sun md extend almost halfway to the next neared Ear. Shorter-period comets, of which more than 200 are known, fall into two groups, He Halley-elass domed that are probably captured from the Oort cloud comes' md the Jupiter-family comets thy usually have orbits near He same planes as those of the plme~ md ~~ originate in the Kuiper Belt, ~ donut-sh~ped distribution extending from He orbit of Neptune to ~ least SS astronomical Unix (AU).~7 More than 500 individual objects in the Kuiper Belt have Greedy been depleted' md about 100~000 with sizes greater ~m 100 km are predicted to exist. An urn own fraction of He bodies in the Kuiper Belt are binaries mirroring the Pluto-Charon bind system. Dub permeates He solar system. Some of it result from the aetivi~ of comets, some comes from He eollisiona1 disintegration of asteroids, md some is in~rs~llar dust passing Trough He plenary region as He Sun md plme~ move among the stars. Some of the smallest dust grains condensed directly from gas in He solar nebula. Other in~rplme~ry dub may have origins yet undiscovered md unexplored. I - brat C~`ons Questions thy emerge from He study of He varied md distribution of primitive bodies in He solar system include He following: Are Here undiscovered populations' such as asteroids interior to Ens orbits What is the radial distribution of dust in He solar system: What is the frequency of binary systems among asteroids md hms-Neptunim objects: What is the orbital distribution of long-period md new comet What are the orbital md size distributions of Cen~urs md Kuiper Belt objects:

pRIM~E BoDIES Future D`~`ons ~7 Surveys are in progress arid plied for the detection of additional bodies in ~e known populations arid for the exploration of their distributions arid physical characteristics, but severe limitations are imposed by available facilities. Special search syzygies must be developed for exploring each known population arid for discovering other populations; proposed new ground-based facilities are well suited to the variety of searches required. The exploration of the dusidishibution cart be directly addressed by spacecraftcarrying the appropriate ins~ummt~ion on marry different trajectories through the solar system, as well as by missions designed specifically for dust studies. Pro~ses Lending to the Formation of Primitive Boilies Plar~simals formed arid grew in the solar nebula as in~rs~llar dust, ice, arid gas condensed into solid object of tangible si=. The plar~ets formed by ~e accumulation of plar~simals ~ various di~ar~ces from ~e Sun' but some plme~simals were captured after ~e Clarets formed' arid became sa~lli~s.~° Between Mars arid Jupiter' hewed arid degassed plar~simals accumulated to become asteroids, some of which subsequently melody eider wholly or partially. At grower dietaries from ~e Sun, ices of several kinds from the primitive solar nebula were preserved as major constituted of most solid bodies. While some primitive bodies appear to have formed their present heliocentric disagrees, other were gravitationally sectored by the planets. Some primitive asteroids' domed, md planets satellites are fragment of larger objects produced by collisions among the bodies that originally acereted in We solar nebula.2i I - ort~t C~`ons Questions that emerge with respect to processes leading to the formation of primitive bodies include We following: ~ What was the chronology of formation of small bodies, md how md when did Pluto-Charon md some Kuiper Belt objects become binaries: ~ Where in We solar nebula did the classes of primitive bodies form: Which were subsequently hmspor~d' md which remain in place: ~ How did He Kuiper disk md the Oort cloud form' md what degree of compositional mixing is preserved: What forces caused He orbits of the Kuiper Belt objects to display such ~ wide rime of inelin~iom md eeeen~icities: ~ What was the balance between accretion md eollisiona1 destruction Usurious heliocentric dimples during the formation of the solar system: Are Here Trojan populations for Saturn, Urmus' md Neptune: When md how were He irregular satellites of the gist plme~ captured: Future D`~`ons ~namiea1 studies with improved eompu~tion~ tools will continue to shed new light on problems of He formation md interactions of He primitive bodies of the solar system through time. llemote-sensing observa- tions particularly spectroscopy, radiometry' md photometry of the physical properties of primitive bodies will help clarify their surface compositions, leading to improved taxonomy md ~ better understanding of their eondi- tions of origin. Analysis of the surface structures seen in spaceport images of key objects will improve our understanding of their fragmentation md eratering histories; such information bears directly on He d~amiea1 history of primitive bodies in various regions of the solar system.

Is HEW FR0~ IN =E 50~R HIM Physical Pro~ses A~e~ing the Evolution of Primitive Bodies Since Their Formation Primitive body surfaces, memories, arid in~rplme~ry dust particles carry information about some of ~e processes of space weathering arid surface modification endured by them materials since the origin of the solar sys~m.22 These processes include solar heating md bombardment by cosmic rays arid microme~oroids, but other processes may have occurred. Some memories contain unaltered in~rs~llar myriad thy condensed before ~e formation of ~e Sun arid plar~ts, while over memories come from parent bodies thy have ~~n melted arid differentiated' arid still others show evidence of interaction with liquid wear (some even contain inclusions of wa~r).~ hIe~ori~s from primitive parent bodies are replay with complex organic molecular myriad arid win wear bound in ~e minerals. Collisions have played ~ commar~ding role in the evolution of primitive bodies, as evidenced by fragmented surface layers, irregular shapes, arid fragmented soils preserved in some memories. Collisions also produce dust thy is mixed in urn own proportions win the dub from evaporating domed; ~e combination of Base materials forms ~e zodiacal cloud md ~e source of in~rplar~ary dust particles Jeeps) collected in Earths stratosphere for laboratory study. I - Brat C~`ons (questions thy emerge from this discussion of ~e physical processes affecting the evolution of primitive bodies include ~e following: What processes in the solar nebula Need to alar presolar material: Are comets differentiated, md do they tannin presolar material: What caused the differentiation of some asteroids: ~ What are all of Be space weltering processes that operas on the surfaces of bodies without atmospheres' md how have these processes varied over time: What is the time-history of eollisiona1 every md their consequences ~ various dimples from Be Sun: What are the thermal histories of all classes of comets; do Key become extinct or dormmt: Do Kuiper Belt objects exhibit evidence of transient Biospheres or epochs of interns aetivily: ~ What roles did tidal activity' atmospheric emape' md interns activity play in generating the strongly dichotomous appearance of Pluto-Charon: ~ Are Jupiter-family comets fragments of much larger Kuiper Belt objects' or are Hey Bill near their original size: Future D`~`ons Missions to small bodies throughout Be solar system' particularly missions ~~ return samples, will illumi- nate Be devils of Be evolution of primitive objects. Detailed Isis of IDPs Id meteorites' using established techniques Id Lose yet to be developed, will continue to elueida~ some processes that occur in space, insofar as the record is preserved. Dust eollee~d in space in the vicinily of known domed Id from over locations in Be solar system will signif~emily aid this study' while samples returned from Be surfaces Id subsurface layers of domed Id asteroids will be critical for major advances. Proper duration Id the development of new mal~ica1 techniques are critical to the understanding of returned samples. Theoretical studies of Berman histories of primitive bodies offer additional insights on several classes of these objects. Experiment win hyperveloeily collisions will help clarify some physical processes, subject to the limitations of velocities thy em be achieved in the laboratory.

pRIM~E BODIES Planets Fonned by the Accumulation of Prunitive Bodies In terms of Weir aims arid compositions' the ply fall into four broad categories: ~e ~rrestria1 ply (Mercury, Venus' Early Mars), ~e gas Diary (Jupiter arid Saturn), the ice Tiaras (Urar~us arid Neptune)' arid ~e ice dwarfs (Pluto, plus the Kuiper Belt objects). All of ~e plays were formed by ~e accretion of smaller plar~simals thy in turn condensed from the solar nebula ~ various dismays from ~e forming Sun, but some of the pits may now occupy positions (heliocentric distends) differmt from the Bias of formations The atmospheres of the ~rres~ia1 ply originated in whole or in part from the imply of vol~ile-rich primitive bodies.26~ I - ort~t C~`ons (questions ~~ emerge with respect to ~e formation of pits by ~e accumulation of primitive bodies include the following: How did primitive bodies contribute to ~e vol~ile inventories of the ~rres~ia1 please ~ Did organic matter delivered to early Earth led other ply by primitive bodies trigger the formation of life or provide ~e ma~rials~ When did Pluto md the Kuiper Belt object forms How does accretion work, where do the materials come from, md what is the time scale: How much radial mixing of primitive material took place: What was ~e role of gist impacts in the formation of ~e plmets md Earths Moon: Why is Acre no plmet between Jupiter md Mars: How large are the awreted bodies in the ou~rmo~ solar system: What was He role of gas drag in the early solar system: Future D`~`ons ~namiea1 studies with improved eompu~tion~ tools will continue to shed new light on problems of He formation md interactions of the primitive bodies of the solar system Trough time. Determinations of He densities md compositions of primitive bodies Trough spacecraft remote sensing techniques' md later by study of returned samples' will provide critical information on the materials from which the plmets formed. Laboratory analysis to determine He isotopic signatures of samples returned from primitive bodies are essential to underst~d- ing the development of volatile inventories of the terrestrial plme~. Effects of Primitive Bodies on the Terrestrial Planets since Their Formation The eratering records on the Moon' He ~rreshia1 planets, asteroids' md outer plmet satellites reveal ~ history of bombardment throughout the solar system, from the time of formation to the present.28 Meteorites, the tangible fragments of bombarding bodies, give information on the eollisiona1 fragmentation of primitive bodies md on He times of disruption md imply on Earth all for relatively recent events. ~terplmet~ dust eollee~d in He sh~osphere md in space gives us ~ window on He generic composition of comets md some asteroids, but He eaglet sourness) of this myriad remain elusive. I - arty C~`ons Questions ~~ emerge win respect to He effects of primitive bodies on He terrestrial planets since He plme~, formation include the following:

to HEW FR0~ IN =E 50~R HIM Do impacts lead to discrete arid long-lasting charges in ~e surface-~tmosphere regime: What volatiles md orgar~ics were delivered to the ~rrestria1 ply What fraction of impactors are comets vs. as~roids~ Future D`~`ons Computational studies of ~e interactions of impactors arid Heir targets cart further elucidate the nature of them processes in ~e early arid modern solar system. Surveys of comets arid asteroids will help clarify the flux of them objects in the perry region. The physical properties of near-Earth objects mud be manured to distin- guish between comets arid asteroids; this cm be done with missions to these bodies arid cart be accomplished partly by radar arid other remo~-sensing techniques. Cometary dust must ~ distinguished from ~~roida1 or over (~.g.' in~rs~llar) dust. Expanded studies of the volatiles arid orgar~ics in primitive memories arid Heir parent bodies will War on ~e questions of ~e materials delivered to ~e ~rreshia1 ply. PRIMITIVE BODIES AS llESEllVOIlIS OF ORGANIC MArl~l~kill+ RAW l\IATEllIALS FOR THE ORIGIN OF LIFE The fundamental questions concerning the role of primitive bodies as reservoirs of orgar~ie matter (OM) in He solar system md in exhasolar planetary systems em be summarized as follows: What is the composition' origin, md primordial distribution of solid organic muter in the solar system: What is id present-day distribution: What processes em be identified that erects destroy, md modify solid organic matter in the solar nebula' in the epoch of the faint early Sun' md in the current solar system: How did organic mater influence the origin of life on Earth md other plmets: Is organic mader similarly dis~ibu~d among primitive bodies in over planets systems: Onion and Primordial Distribution of Solid Organic Matter in the Solar System Carbon-rich molecular Madrid condenses in the outflows from evolved stars md is injected into He inter- s~llar medium. Modified by ultraviolet radiation md other processes' this m~eria1 becomes enriched in complex organic molecules ~~ eon silicas dust grains, but it also exists as submieron-size particles consisting entirely of interlocked ring sutures. High-resolution spectra win the Infrared Space Observatory (IS O) spacecraft recently showed ~~ polyeyelie aromatic molecules exist as ~ gas in the interstellar medium' together win condensed species on in~rs~llar grains. The Sun md plme~ formed in ~ fragment of ~ Mint molecular cloud enriched in this organic dust md gas. While some organic maker was destroyed in the solar nebula, new molecular malaria was created as chemical processes in the nebula occurred.~° Later' additional organic molecular Madrid may have formed on the parent bodies of the meteoric. I - omit C~`ons Questions ~~ emerge win respect to the origin md primordial distribution of solid organic matter in the solar system include the following: What is the composition md structure of primitive organic muter in the solar system: Where md under what conditions did orchid muter originate: What are the relative fractions of organic matter in memories md domed ~~ are interstellar md solar nebula in origin: Was primitive organic mater racemie:

pRIM~E BoDIES Future D`~`ons Answers to ~e key questions listed above will come from ~e study of samples returned from well-charac~r- i~d domed arid androids arid from continued astronomical observations of Base objects as well as in~rs~llar moor. The application of newly developed ar~al~ica1 techniques to existing arid future collections of Doris microme~ori~s, Ed sh~ospheric in~rplar~ary dust particles will move this subject area forward. The ar~alysis of dust collected in space is critical to Case issues. Presentably Distribution of Organie Matter Individual grains rich in organic maker are found in carbonaceous memories arid in~rplar~ary dust particles arid are presumed to be ~ fundamental component of comets. The deu~rium Undo in meteoritic arid IDP organic moor is ~e same as is measured in the in~rs~llar medium' providing ~ link to presolar moor in space.32 There is spectroscopic evidence for the presence of complex orgar~ic material on several plar~etary smelliest Centaurs, arid Kuiper Belt objects' arid possibly vermin asteroid classes. On icy satellites arid in He rings of Saturn, the organic material may exist in very small quar~tities ineorpora~d in water ice. On Pluto arid Triton' photo processing of the methane fee may produce colored materials consisting of more complex organic ehemieals.~3 I - ort~t C~`ons Questions thy emerge regarding the present-day distribution of organic maker include the following: ~ Which asteroids (or comets or Kuiper Belt objects) are Be sources of the carbonaceous meteorites of various types, including the mierometeorites: What is the composition of organic mater in non-icy bodies: ~ What are Be compositions of organic mater that color some icy bodies' including Pluto Ed Be Kuiper Belt objects ~ What are the sources of IDPs: Future D`~`ons Answers to the key questions listed above will come from the in situ study of well-eharae~ri~d regions on comet Ed asteroid surfaces' as well as the study of samples returned from comets Ed asteroids. llemo~-sensing observations (speeLoseopy) from missions to small bodies will eonbibute significantly to Be understanding of their compositions. Continued studies of meteorites Ed in~rplme~ry dust particles are eritie~ly needed. Astro- nomiea1 observations of domed, asteroids, Ed planets satellites from Earn Ed from space will expand our understanding of the relationships between meteorites Ed asteroids Ed will contribute to understanding the extent of organic ma~ria1 on primitive bodies, but they are unlikely to determine the organic materials composition. Proses That Create, ~t~y, and Modify Solid Organic Mutter in the Solar Nebula When simple gases or ices (water' ammonia, methane' hydrogen, Ed so on) are irradiated with ultraviolet light or ~ stream of atomic particles (electrons or protons)' chemical eh~ges occur ~~ produce complex polymers Ed other solid residues ~~ are strongly colored. When exposed to liquid water, such material produces amino acids Ed other complex molecules that occur in living sys~ms.3435 The arty MA Ah ;~m ^~ ~ 1 1~ ~1 1~1 ,~' "~O w~ 1 "~ Yr 1= 1 ~ 11~ ~ W1 1 plme~ry bodices em ~ies~oy some of this orgasm material, but it em ore ate new species as well. ~ addition' radiation environment on the surfaces of planets Ed Heir satellites em both cream Ed destroy complex organic molecules, but the deviled conditions Ed the balance between destruction Ed erection are urn own. Processes in space may affect the balmee between He left-h~ded Ed right-h~ded mix of those organic molecu les that have

HEW FR0~ IN =E 50~R HIM the property of chirality, md thus may have played ~ role in the origin of life on Earth' which is based on left- har~ded molecules. I - Brat C~`ons (questions emerging from consideration of the processes ~~ creates destroy, arid modify solid orgar~ic mower in the solar nebula include the following: Are Bore unidentified processes thy create arid destroy organic matters Do natural processes result in racemic mixtures of complex OMIT ~ What are ~e chemical details of the formation of macromolecular orgar~ic solids under differmtoonditions arid win different sorting mixtures What is the Immoral history of orgar~ic formation in various environments in the solar systems What is the balance in the Oration arid destruction of OM in impacts arid radiation environmental Future D`~`ons Laboratory ar~alysis of organic myriad in memories' IDPs, arid returned samples from comets md asteroids is critical to making progress on the key questions listed above. Laboratory synthesis of complex organic win simulated plenary materials md environments will play ~ key role in underfunding He genesis md evolution of this myriad in primitive bodies. llemo~-sensing observations from missions to small bodies will contribute to understanding He processes that modify materials in the space environment. How Did Organic Matter Influence the Origin of Life on Earth and Other Planets' Organic molecular material' bow simple md complex' existed in He solar nebula md was included in acereting plmetesim~s ~ ices md over solids of low vol~ilily. Comets md Kuiper Belt objects are presumed to contain such material in Heir ices' while sever al classes of meteorites originating in the asteroid belt also contain large inventories of amino acids' earboxylie acids' md so on.36 Asteroids md comets impacting Earth md over terrestrial plme~ during the 1~ heavy bombardment delivered vast qumlities of these materials, perhaps providing the raw materials for the origin of life.37 I - Stat C~`ons Questions that emerge from studies of how organic maker from primitive bodies influenced the origin of Life on Earn md other plme~ include He following: ~ How does refractory OM v~ among He homed, asteroids, planets satellites' md other solar system bodies, md what does this tell us about the ehemie~ environment in which it formed: ~ What kind md qumlities of OM delivered to early Earth md other terres~ia1 planets survived the impact md He planetary environments ~ that time: Did exhaterreshia1 organic mater trigger or provide the feedstoek for early life on Eared Where else in the solar system does life exist or has it existed: Could He ~rres~ia1 L-en~tiomer preference result from the ehiralily of extraterrestrial OM: Future D`~072s While key questions em be formulated in He context of planets science, the future directions in this area of how OM from primitive bodies influenced He origin of life on Earth md over plme~ are probably in the field of biology. In terms of He exis~ee of fossil or contemporary life elsewhere in the solar system, exploration is He

pRIM~E BODIES only tool available. Samples resumed from primitive bodies will shed light on these questions in ways thy no other source of information cm. Is Organic Material Similarly Distributed A~ng Primitive Boilies in Over Planetary Systems' Marty sirs are surrounded by disks of dust showing structure suggestive of ~e presence of ply. This dust is presumed to contain ~ mix of silicons arid macromolecular carbon molecules preserved from the in~rs~llar clouds in which the Bars originated. One such star win ~ dust disk, ,8 Pictoris' exhibits spectral flashes thought to result from the impact of domed into it. ~ addition, ~e recent diction of wear in ~e outflow of ~ carbon-rich red girt Car by ~e Submillime~r Wave Astronomy Sa~lli~ (SWAS) spacecraft suggests thy ~ large number of comets are being vaporized in its extended ahnosphere. Discoveries of Saturn- arid Jupiter-size planets surrounding about ~ percent of solar-type stars in Me Milky Way galaxy39 further suggest ~~ primitive comets arid asteroids are relatively common in mmy star systems; they may be repositories of orgar~ie material preserved from Me molecular clouds in which those Mars arid plar~e~ originated. I - arty C~`ons (questions ~~ emerge from studies relating to the distribution of organic myriad among primitive bodies in other planetary systems include the following: Are Mere planets in the habitable zones around other stars95 What are the eharae~ristie signatures of primitive body reservoirs around other stars: Is our assemblage of primitive bodies typical: Future D`~`ons Numerical modeling md ashophysie~ observations of over star systems win indicators of He presence of plme~ will address the key questions listed above. SPACE MISiSIONSi FOR THE EXPLORATION OF PRIMITIVE BODIES While certain missions are expected to fall within the cost framework of He Discovery program' the Primitive Bodies Panel focused on missions that appear to exceed the $325 million Diseovery~lass limit but that are expend (when competed) to cost less thm $~50 million. These are termed <`medium elass.~' Missions ~~ are expend to cost in excess of $~50 million are called large-class missions. Medium-C1n~ Missions Kipper Bek Auto Explorer A reco~aissmee mission to two or more Kuiper Belt objects md Pluto-Charon . is ~ He top of the Primitive Bodies Panel rankings because of in compelling importune to the scientific objectives identified by He panel. The eve payload of the Kuiper Belt-Pluto (KBP} Explorer should include imaging md spee~oseopy in He ultraviolet, visible, md infrared, uplink radio science, ~ suite of measurements of particles md plasmas' dust detectors' md ~ high-resolution imager. Throughout this report' the word+ llhabit~le>' is use+ ir1 ~ ~~era1 surly me~irlg compatible with any kirld+ of life. When llh~it~le>' is use+ to me ~ compatible with hums life' the text specifies that.

~4 HEW FR0~ IN =E 50~R HIM This mission will mark ~e begi~ing of the exploration of ~e Bird grew geographic zone of ~e solar system' the region beyond ~e gimt ply. The science objectives for ~ suite of Kuiper Belt object thy could ~ Tidied sequentially by relatively small charities in course as ~ first spacecraft flies deeper into the ~ar~s-neptunim region include But are not limited to) ~e following: I. Vermilion of the dimensions arid shapes' 2. Vermilion of order density' 3. Measurement of surface composition through imaging spectroscopy, 4. Detection of atmospheres, S. Detection of evidence of arty current geological activity ~.g.' geysers)' arid 6. Measurement of dust density with ingrowing heliocentric dismay in ~e Kuiper Belt. For Pluto arid Charon' the scientific objectives identified md prioritized by the Pluto Express Science Definition Team (VELDT) should be met or exceeded.40 The science ~ Pluto arid Charon is time-critica1 because of long-term masona1 charges in the surfaces arid atmospheres of bow bodies. Surface Scathe Goads. The Dory objectives of surface mapping md surface composition mapping of Pluto md Charon established by the SOT would be signifiem~ly compromised without ~ early mission.4i This is due to Pluto-Charonts ongoing approach to ~ steep solstice geometry that increasingly hides in shadow large exposes of polar terrain on each object (~200~000 km2 of terrain will be lost to imaging md speetromopie mapping on Pluto alone for each year of arrival delay between 201~ md 2025~. Beyond Be proportional damage thy this does to Be global geology md composition mapping objectives ~~ Be SOT set for He mission' this loss of terrains will also severely affect Be ability to answer key questions about the extent md nature of the polar volatile reservoirs on Pluto' Be origin of the polar cap dichotomy on Pluto' md Be possibility that vol~iles capable of generating atmosphere on Charon are sequestered in polar regions. Atmospheric Science Good. Concerning atmospheric science' Pluto is withdrawal from perihelion is widely mticipa~d to result in ~ subs~tia1 deeline'42 if not ~ complete eollapse'43 of id vapor-pressure-suppor~d atmosphere.44 Searches for ~ atmosphere around Charon' ~ extremely desirable mission objective called out in the SOT report, will also be adversely affected' or wholly lose as will be the opportunity to study Ionospheric transfer between Pluto md Charon something unique in Be solar system as far as we know. Over Ionospheric science ~~ will be lost ~ Pluto if the atmosphere collapses or signifiemily declines before mission arrival will be the ability to do the following' among other things: Test for hydrodynamic escape (a mandatory objective), Determine Be base pressure md vertical h~e/~mperature structure of the abno sphere that has been under study since the I98Os Avower Dory objective), Pin down volatile Disport rates (m extremely desirable objective), md Sample Be atmospheric ehemisLy md Be production of organdies md nitrites during id maximum pressure (i.e.' perihelion) sate (mother Dory objective). Comet Surface Sample ~~um~amp~s from ~ Seemed Surface ~m The Primitive Bodies Pmelts second-r~ked medium-class mission is Be return of samples from ~ selected surface sin on Be nucleus of ~ comet. The science from this mission was considered more importmt than that from the Kuiper Belt-Pluto Explorer' but two fundamental differences arise related to readiness. First, Were are several well-developed designs for KBP missions already available' whereas well-developed designs for ~ Comet Surface Sample lectern (~81~) mission are not available. Furthermore' there are engineering concerns about Be viability of ~ surface sample-return mission relied to the up own nature of the comet surface. While most

pRIM~E BODIES ~5 cometary scientists Wink ~~ the ma~ria1 is relatively weak arid therefore easily sampled in ~ ``grab-md-go,' mode, only the Deep Impact mission is likely to resolve Dose engineering concerns as Ming either justified or not. This implies ~~ the CSSR is most effectively Shun Mar July 2005, when the results from pep Impact will be known. No other class of objects cart ~11 us as much as samples from ~ selected surface sip on ~e nucleus of ~ comet cm about ~e origin of ~e solar system md ~e early history of wear arid biogenic elements arid compounds. Only ~ returned sample will permit the necessary elemental, isotopic' organic, arid mineralogical measurements to be performed. Although it is desirable to return ~ nucleus sample ~ ~ temperature sufficiently low to preserve the full suite of ices, ~e highest priority is given to ~ mission returning the full quip of org~ics arid non-i~ minerals together with wear maintained ~ ice ~ mission ~~ is technically achievable in the next decade, arid which ~e parted believes might be achieved in the medium~lass Memory. High priority should ~ given to resuming sample from ~ comet thy has been previously visited by spacecraft or is charw~ri~d by ~e sample-collecting spacecraft itself' in order to permit ~e maximum in~rpretabilily of information to ~ obtained from the comet. In the first sample-return mission from ~ comet ~e myriad could be collected ~ one or more sites on ~e surface or in He near-surface layer, preferably in or near art active vent. It is recognized thy this kind of mission does nof address the full rape of scientific issues ~~ could be accomplished by ~ mission in which samples were collected from severe regions on He nucleus, including the subsurface (by drilling), win He specimens resumed ~ deep cryogenic ~mper~ures. However' this more complex mission is thought to be outside the cost framework of the medium~lass envelope. In my case' if ~ nucleus sample-retum mission coot be accomplished within He medium-class category, it should receive the highest raking in the category of large missions. The panel strongly recommends ~~ the entire Comet Surface Sample lletum mission be commend through ~ Announcement of Opportunity as was done for He K13P mission. Trojan Asmro`~Cenmur I The Trojan As~roidiCen~ur llecormaissmee mission would send ~ KBP-like flyby recor~E~aissmee space- er~ equipped win imaging, imaging speeboseopy, radio science' md, potentially, over instruments to make He first explorations of bow ~ Jovian Trojan asteroid md ~ Centaur. Beyond simply opening up these two new classes of primitive bodies to exploration, this mission has deep ties to understanding the origins of primitive bodies. In particular' He Trojan flyby would sample primitive material from the Jovian accretion region of the nebula; it would also allow ~ imports reealibr~ion of He bombardment flux on objects in the Jovian system md would offer new insight into space weathering md other processes affecting asteroids' particularly in the main belt. The Centaur flyby would provide insights into the nature of the Kuiper Belt, the nature md origin of short-period domed md their parent bodies' md aetivily in disks comets. Such~missionembeeonduetedwi~eurrent~ehnology' using ~heavy-liftexpendable launehvehiele ~LV) such as the Delta IV 4050H; if ~ Centaur inside ~~.S AU is selected, it is possible to carry out this mission using large photovol~ie arrays' thereby avoiding He need for ~ radioisotope power supply. Such ~ mission would very likely also be capable of ~ main-belt asteroid flyby during its trip from the ironer planets region en route to He r ~ room zones. Aswarm lope film The Near-Ear~ Asteroid llendevous (NEAR) mission to 433 Eros demonstrated that even small asteroids are covered win complex md sub~mtia1 regalia which are heterogeneous in texture md detailed in composition (Figure I.2~. To understand the geologic evolution of asteroids, regoliths must be studied in devils md their variability must be characterized bow vertically md horizontally. NEAR has shown ~~ He surfaces of asteroids em be so heterogeneous ~~ it is difficult to identify ~ single "representative,, locale. What is needed is He ability to led remote-sensing md mal~iea1 instruments md to provide the landed package with mobility in order to access ~ variety of geologic sips. The abilily to return samples for detailed analysis on Earth is also essential. Such ~ mission would address the nature md time sexes of geologic processes on asteroids md elueida~ how

HEW FR0~ IN =E SOLAR MOM FIGURE 1.2 Though covered with rocks and boulders, the surfed of asteroid 433 Eros uppers to lack small craters. Thou ~t are On are mu - , subduing ~t the surfed is covered with ~ blokes of regolith. The' two images were Akin by the NEAR Shoemaker spacecraft from ~ altitude of 3~: km ~zgh~ ~d 7 km ~~) and show features as small as ~ ~d 1.4 ma respectively. Soured of Appli~1 Physics Laboratory.

pRIM~E BODIES ~7

Is HEW FR0~ IN =E 50~R HIM them work to modify the texture arid composition of ~e regolith. It would also provide ~ detailed compositional charac~riz~ion of the Steroid. To maximize ~e science retum from such ~ mission, it is essential to sel=t the most interesting locales on ~e asteroid, ~ goal thy implies ~ global recormaissar~e of ~e target body. ~ this context ~ follow-up mission to asteroid 433 Eros should ~ given high priority. Eros represents ~ well~harac~ri~d' importers target on which potentially interesting sins cm ~ sel=~d from existing dam. Eros also represents ~ Argot ~~ is relatively easy to reach d~amic~ly arid on which ~ successful lading has already been demonstrated. Tri~ept=e Flyby The Tritor~Neptune Flyby mission would send ~ Gemlike flyby recormaissmce spacecraft equipped win imaging' imaging spectroscopy' radio science, arid potentially over instruments, to make ~ deviled second reco~aissar~e of ~e Neptune system. Using ~ Jupi~r-gravity assist such ~ mission could ~ launched in 2007' reaching Neptune in 201 S. A Centaur flyby en roux to Neptune is possible; ~ post-Neptune flyby of ~ KBO is also possible in ~ extended mission. The primary target ~e Neptune-Triton system' is scientifically rich (see Shapers 4 arid ~ in this report arid would grimly benefit from ~ follow-up to Voyager. Such ~ flyby would bring to bear new Ethnology instrument (em.' infrared mapping spectroscopy) arid would allow time-variability studies. This mission cart be conduced with current technology' but it does require ~ radioisotope power supply. In addition to being deeply attractive to the primitive bodies community, such ~ mission would be appealing to Pose researchers interested in studies of He large smelliest planetary rings' md the gist plme~ the latter, in particular, if it were feasible to include ~ Neptune atmospheric probe. Another feature of this mission commending it for additional study is that it would provide ~ mems of sidestepping the return-to-Neptune cost md technology dilemmas imposed by current thinking about Neptune orbiter missions. Large ~[is~om The panel identified ~ single high-priority mission in ~ cost Amatory that even with competition' is expend to exceed Me cost of medium-class missions. Comet Cryogenic Sample ~~m Cow Sampan from kept Because of the grew importune of sample-return missions from comets to future progress in understanding the origin md development of the solar system md because of He limitations imposed by cost on ~ medium-class mission, He panel suggest that ~ larger-scale mission to one or more domed be undertaken. Such ~ mission would collect samples of ~ well-eharae~rized comet nucleus from two or more selectable sites, both from He surface md from ~ depth on He order of ~ m. ~ order to preserve He full suite of volatile materials, He samples would be maintained ~ ~ temperature below IS0 K Trough He return to Earth for analysis. A mission of this eomplexily requires further technological developments, particularly for drilling md sample eolle~ion md for cryogenic preservation md return to Each. KEY ENABLING TECHNOLOGIES FOR PRIMITIVE BODY EXPLORATION The panel considered areas of ~ehnologiea1 development ~~ are required to enable certain highly desirable missions. Those areas (in no p~ieular order) are as follows: ~ Driving on smad bodies. Techniques must be developed in order to collect samples of comets md asteroids below the exposed surface md deep into He region where volatiles may be retained. These samples will then be returned to Earth for analysis.

pRIM~E BODIES Cryogenic campy pro a~d doing. Techniques mud be developed for the return of samples of domed to Earth for ar~alysis. ~ order to retain the critical volatile components of ~ comet nucleus in samples collected below the exposed surface, the temperature of ~e sample must ~ maintained ~ less Bars IS0 K during the collection' encapsulation, lift-off from the nucleus, md return md capture ~ Earn. Techniques for hurdling arid Cysts of cryogenic samples in ~e laboratory must also ~ developed. ~ Promos age ~~rm~oon ~d compos`~o~f~l I. Techniques must ~ developed to be performed robotically ~ relend sins on primitive bodies (asteroids, comets, perry sa~lli~s, arid perry surfaces) in order to provide cost-effective ways to explore the cosmochemica1 properties of critical bodies in ~e solar system. ~ Nuclear - lectnc propub~on. This Ethnology requires development so ~~ it cart ~ implemented 1^ in this decade or as soon there after as possible. KEY SUPPO1ITING llESEAlIC1I AM FACILITIES Nenr-Enrth Ohje~s Near-Ear~ object (NEOs) are asteroids' spent comets' arid active comets the approach ~e Earth-Moon system md thy in some cases may constitute art impact heard of global proportions. Indeed, governmental studies in He United Stress the Uni~d Kingdom' arid elsewhere have requested surveys for near-Ear~ asteroids in search of objects that may constitute ~ impact heard. More thm ~ statistical study' governments desire ~ Wallop of potential impaetors ~~ would produce global catastrophes or widespread damage on smaller scales in the next century. Surveys in progress have identified ~ estimated 50 percent of He near-Ear~ Steroids md extinct domed ~ km md greater in size' md very roughly 10 to IS percent of such bodies 0.S km in size. Approximately 340 (as of November 2001) of these come especially close to Earth md are exploded as Potentially Hazardous Asteroids. The number of new comets with impact potential is large md us own. Importmt scientific goals are associated with He NEO populations, including their origin, fragmentation md ci~amiea1 histories' md compositions md differentiation. These md over seientif~e issues are also vim to He mitigation of He impact h=ard, as methods of deflection of objects potentially on course for ~ impact with Earn are explored. Information especially relevant to heard mitigation includes knowledge of the interns structures of near-E~h asteroids md comets' Heir degree of fracture md He presence of large eve pieces, the fraeta1 dimensions of their structures' md their degree of cohesion or friction. The scientific goals of near-Earth object studies for He objectives of both pure science md science for He public good should be addressed in ~ aggressive' multidimensional program of detection md physical studies with Earth-based telescopes, including radar, md perhaps telescopes in space. In addition, high priority is given by the panel to missions to representative objects (en., 433 Eros) to establish Heir physical properties' as noted above. Samples returned from near-Earth objects are ~ critical component of these objectives. Accordingly' He Primitive Bodies Panel recommends ~ medium-class mission to led on ~ asteroid, possibly 433 Eros' collect samples from several well~harae~ri~d locations' md return them to Earth for analysis. Diseovery-elass missions for the reco~aissmee of additional near-Ear~ asteroids md extinct comets are also recommended. The panel further recommends thy dedicated md powerful ground-~ased facilities for He deletion md physical study of near-E~h objects be implemented, together with the d~-h~dling md da~-malysis capabilities ~~ large-scale surveys will require. Additionally' adequate support is critically needed for the analysis of dam from missions to near-E~h objects, as well as ~eoretiea1 studies of the eosmoehemieal, geophysical, geological' md d~amiea1 evolution of such objects md their precursor bodies. Earth-~ed Teles In He decade under eonsider~ion, ground-based telescopes will continue to play key roles in He detection md physical study of primitive solar system bodies. Asteroids near Earn md in He main belt are found md studied with ground-based telescopes, as are Kuiper Belt objects, Centaurs' divot domed' md mod plmet~ Bellies. It is essential ~~ ground-based Lopes suited to a11-sky surveys md other deletion strategies be included as

So HEW FR0~ IN =E 50~R HIM in~gra1 component of the next decade of solar system exploration. Equally importmt are ~lemope facilities capable of spectroscopic, photometric, radiometric, arid radar investigations of known arid newly discovered small bodies in the solar system. Win some exiting arid proposed facilities' the objectives of detection arid physical studies cart be met with the same ~lemope equipped with ~ variety of supporting ins~umen~tion. Earth-based facilities ~ broader term encompassing not only ground-bamd telescopes but also airborne telescopes (notably' ~e Stratospheric Observatory for Infrared Astronomy [SOFIA]) arid near-Earth spaceborne telescopes (~.g., the Space Infrared Telescope Facility [SIRTF], ~e Hubble Space Telescope EST]' md the James Webb Space Telescope [TWST]) will play critical roles in the study of solar system bodies in wavelength regions inaccessible from the ground' md ~~se mud be supported. Marty solar system observations impose special requirements on telescopes (for example, because of moving targets' faint objects near bright plar~ts, arid the need O ~ for high definition)' md it is importers ~~ newly defined projects for telescopes on all platforms include ~e chnologica1 options ~~ will enable obtrusions of solar system bodies. Telescopes on the ground' in the air, md in space afford observations of vastly more object chart cart ever be visited by spacecraft. They not only enable us to select appropriate targets for spacecraft vising but also let us put into eons He information gained from expensive arid infrequent space missions to asteroids, comets, md other primitive solar system bodies. Numerous examples could be given of the critical value of mission support afforded by observations win telescopes of various kinds; ~ few are mentioned here to help underscore He breadth of He concept of ``mission support',: ~ The Galileo probe entered Jupi~rts atmosphere in ~ anomalously eloud-free region whose strong infrared emissions were detected by NASA's Infrared Telescope Facility (I1lTF) on hound Kea. Without this information' the context of the information relayed by the probe would have been lost. The Kuiper Belt-Pluto Explorer mission currently under development is intended to visit Kuiper Belt objects that probably have not yet been discovered. The eventual targets will be detected by ground-based surveys of the appropriate volume of space. ~ A mission to ~ presumed org~ie-rich asteroid will have to be ~rge~d ~ ~ object that has been observed md classified from Ear~-based observations. ~ A mission to ~ dynamically new, inbound comet would require either dramatically improved discovery eapabilily for domed ~ large heliocentric disagree or ~ mission <`ready to go'', either on He ground or already in heliocentric orbit. This broad definition of mission support eh~lenges NASA to be forward-thinking md inclusive, so ~~ ground- based telescopes em find forged, define basic parameters, md motivate key science questions that em only be addressed by spaceport. Mmy of He observational requirements for solar system objects are fully as challenging ~ the faintest md mod difficult objects in modern astrophysics md thus require very large apertures' highly sensitive detectors' versatile spectrographs, md other supporting inshument~ion, often with special features to enable observations of moving targets md faint targets that are nearby bright plme~. The SSE Surveys Primitive Bodies Panel endorses He concept of ~ large telescope capable of ~ all-sky search stringy that would reveal large numbers of near-Ear~ objects ~ well as trms-Neptunim objects, Gus completing the surveys of these objects to ~ brightness level much beyond the current capabilities. The Primitive Bodies Panel also endorses ~ telescope ~~ would enable He physical study of such objects by spee~oseopie md photometric techniques. The panel heard recommendations for the Large Synoptic Survey Telescope (LSST) md the Next Generation Lowell Telescope (NGLT)' both of which enable surveys md physical observations ~ some level that exceeds current capabilities. Other options' including He Panoramic Optical Imager concept, should be explored md ~ choice made that NASA em support in the next decade.

pRIM~E BODIES FIGURE I.3 Multiple roar onion of ~e main ~1t asteroid 216 Kleopaka revealed ~e rotation of his unusual object. At ~e time 0t ~~ ob~rv~ions were man win ~e plenum roar facility ~ ~e Ar~ibo Observatory Puerto Rico, Kleopaka was some 171 million kilometers from Earn. Specko~opic studies Indian that his 217-km- long object has ~ metallic composition. Mourns of N~iona1 Acronautics ~d Span Adminisk~io~J~ Propulsion Laboratory. Support for E;x`~ng F~s Pl~et~y R~=F=~'es. The pme} heard ~ presentation on He status md future of the plme~ry radar facilities ~ Areeibo, Puerto llico' md Coldstone' California, as Hey are used for studies of small solar system bodies (Figure I.3~. These highly productive facilities provide unique information on the shapes md sizes, regoli~ properties' md occurrence of binaries among near-Earth obeyer' md provide critical astrome~ for orbit predie- tions. Bow facilities are working ~ their timid in terms of equipment md persormel. The d~-acquisition systems ~ both facilities urgently need upgrading' md He staffing is insufficient to hmdle He observing workload imposed by He increasing numbers of near-Earth objects being discovered md requiring follow-up observations. lleplacements for near-term retirement of rarities Ethnical staff are urgently needed. The pme} recommends that both of these impor~t facilities be supported md upgraded as needed, for the unique information that radar observations of small solar system bodies provide. Me klAS;A Infrared Telescope Foamy. The I1lTF' mentioned above' eonLibu~s to ~ wide spectrum of solar system md astrophysics investigations by U.S. md foreign astronomers md makes ~ special eon~ibution to He study md characterization of near-Earth objects. ~ particular' in ~ focused effort on small bodies md win dedicated observing programs' instrumentation, md rapid response time, the I1lTF will contribute critical informa- tion for plying space missions to domed md asteroids. Even in ~ epoch of 6- to lO-m telescopes, He contributions of He 3-m-aperture I1lTF are very important to He next decade of solar system studies, md He panel recommends that requested upgrades to the facility be made to ensure operations ~ ~ ~ate-of-~e-art level.

HEW FR0~ IN =E 50~R HIM ~e Eeck Telescopes. Some ~ ~ percent of the observing time on ~e twin 10-m ~lemopes ~ ~e Keck Observatory on Mauna Kea is available for studies in areas selected by NASA. These studies are defined in ~ priority order with in~rferome~y first, diction of ex~asolar pits wcond, arid general solar system Agronomy Gird. The result is ~~ very lidle time is available for general studies' for example' of KBOs. The Primitive Bodies Pme1 recommends ~~ NASA's commitment be sustained ~ ~ high enough 1~1 thy scimlif`~ally importers problems in solar system astronomy such as physical charac~ri=tion of KBOs, cart be carried out with this facility. or~ory Fates for Reamed Samples. It is critically importers to prepare for the sample returns from ~e Stardu~' Genesis' arid Muses-C arid ~e ar~ticipa~d returns from Mars arid ~ comet nucleus by ~e establishment of ~ realistic laboratory instrument~elopment program. Exiting programs of this nature are dramatically under- funded. Initial funding should be aimed primarily ~ the development of new ar~al~ica1 technologies' with ~e mod urgent need King for ~e development of orgar~ic chemist microm~ysis. As new techniques are est~- lished' ~e program priorities should shift to upgrading U.S. laboratories win the new ar~al~ica1 equipment. Laboratory Facilities for the Study of Planetary Materials Laboratory studies in support of observ~iona1 studies' arid particularly NASA plar~e~ry missions to placed' comet, arid asteroids, are critical to the correct arid complete interpretation of the dam acquired ~ grew expense. Such work is inadequately supported either in existing laboratory facilities or through the erection of new labora- tories. The Primitive Bodies Panel recommends that as long as sample-return missions are in the mission plm' there is ~ continuing need for upgrades to He equipment used for analyzing Be samples ~ levels currently in NASA's Sample lectern Laboratory Instruments md D~a Analysis program. Curat~on A critical neeessily in preparation for the sample returns from the S~rdust Genesis' md Muses-C md Be mticipa~d returns from Mars md ~ comet nucleus is support for sample Torsion md handling ~ ~ signif~e~tly increased level over what exists today. The proper preservation of each returned sample for future investigations is of paramount importune. The samples returned from each object will have particular handling md storage demands, which mud be addressed by separate, specialized facilities. The funding for these facilities, including long-term operating costs, ergot realistically come from each missions budget. In particular, development is required in Be areas of eryocur~ion, robotic sample handling, md hiologiea1 quarantine. The panel recommends that Be facilities required for the proper analysis md Torsion of returned samples be developed md supported. KEY QUESTIONS AND MEASUREMENT OBJECTIVES The impor~t questions identified in each of Be thematic sections above are merged here into key scientific questions thy are amenable to solution in Be decade under consideration by ~ series of space missions md surveys of Be solar system from Ear~-based observatories' as well as expanded laboratory facilities. These questions are presented here' condensed md reframed' in Free categories of expend impact. The panel measures Be impact of ~ question by asking whether its answer has the possibility of erecting or echoing ~ paradigm, whether Be new knowledge might have ~ pivots effect on Be direction of future research' md to what degree Be knowledge that might be gained would subs~ti~ly strengthen the factual basis of our understanding. These measures of merit are listed in Be order of the priority that Be panel associates with them. Primitive Rode As Building Bloc of the Solar System Potentially paradigm-al~ring questions about primitive bodies as building blocks of the solar system include the following:

pRIM~E BODIES What is the population structure of the solar systems - What is the nature of Kuiper Belt objects What is the formation history of the trms-Neptuniar~ regions ~ Where in the solar system did building blocks form; which were Respond arid which were note (questions of pivotal imported include ~e following: of origins - How do compositional differences ~twem the Oort cloud arid the Kuiper Belt bodies relay to their sins - Are small' diary bodies such as Kuiper Belt objects, Pluto' arid Charon geologically active todays What is the nature of binary objects in He solar system' arid what do Hey ~11 us about formation history - What processes modify the surfaces of all Agonies of building bloeks~ Found~ion-building questions are as follows: How do colors arid albedos of small bodies relay to Heir compositions arid histories of Lion by various processes since their origins ~ What roles did various d~amiea1 processes play in the origin arid evolution of the primitive bodies in He solar system, Ed what were the time scales: ~ What are He orbital distributions of long-period Ed new comets, Ed how have these distributions evolved over the age of the solar system: Primitive Bodies As Reservoirs of Organic Matter Potentially paradigm-altering questions about primitive bodies as reservoirs of organic maker include He following: - What are the compositions Ed origins of He organic Ed volatile marries in primitive bodies: How is organic mater dis~ibuted throughout He solar system: What is the chemical Ed isotopic composition of comet surface materials: ~ What are the physical Ed ehemie~/isotopie properties of comet nuclei' Ed do they vary win depth Questions of pivotal importune include He following: Did organic mater from domed Ed memories provide He feedstoek for the origin of life on Earth: ~ What are He pared bodies of He carbonaceous memories' in~rplmetary dust particles, Ed mierometeori~s: Found~ion-building questions are as follows: - What are He processes by which organic myriad forms on the surfaces of icy Ed over primitive bodies 'n the current epoch: ~ What is He thermal Ed aqueous alteration history of the parent bodies of He org~ie-rich primitive meteorites: Table 1.l shows the themes Ed questions identified by the Primitive Bodies Panel Ed He imply of specific missions Ed surveys toward their resolution. The two themes around which this shaper is organized primitive bodies as building blocks of the solar system' Ed organic maker in He solar system as materials for the origin of life are equally important Ed urgent. The key questions for each theme are listed in He order of importance in the sense of representing He sups needed to address He themes. Table I.1 represent He Primitive Bodies Purely best judgment of He extent to which each

~4 .= . _ - . _ o . _ .~ C) . .~ C) 4- . . . .~ .= .s Can it. o o ~ CL EN ~ 4 ~ so ~ E~ V CL ~ a CL V O _, _e - _, V ~ _, ED qua O _, 03 V o et ~ 1- ~ _, ED En' ~ O ~ ~A~ ~ ~ ~ ~ ~ ~ O O ~A, ~ O U ~ ~ O ~ ~ ~ ~ —~ ~ O —~ o O t. O ,~ i= CAM CAM CAD ~ _ _I _ _I _ _I ~ 4~ 4~ 4~ ~ ~ ,= ,= ~ ~ - -~ ~ -~ ~ __I __I ~ O O O O ~ V O ~ ~ O 4~ ~ A ~A~ 4_ 0 O ~ O O O O 4 ~ ~ o ~ ,~ 0 4—~ A O Cd ~ _, ~ !_ ~ T~ ~ ~ - O - ~ C`~ ~ ~A~ O ~ O ~0 ~ .~ A O . O __I O ~A~ ~A~ _~ ~ o `. 00 O ~ ~ O ~ -~ ~ ~ ~ ~A~ ~ =, ~ 4~ 4~ 0 ~ ~ o ~ 4~ ~ 4~ C~ ~= ~A~ ~ O Cn ~ ~ ~o ~A~ ~ ~ ~ ~ O ~ ~ O >_ ~ _ _1 4_) ~ ~ _G _s O ,~ 4 o !_ -~ ~ ,~ =, ~ _ _~ ~A~ ~A~ ~ ~ O ~ ~ q~ ~ O ~ ~ ~ O O -—I T; ~ ,~ >_ oA~ ~ ~ ~ -~ ~ _. ~A~ ~ O ~ ~ ~ ~ ~ ~ O O ~ ~ ~ O ~ ~ ~ ~ C) ~ ~ -~ 0 4~ 0 O O ~ O ~ ~ ~A~ ~ _ _ _I - q_ ~ ,~ C~ O o A ~A~ 4~ O ~ ~ LIA~ ~ O C~ ~A~ O ~ __I ~ ~ 4_ =, O O O ~A~ ~ o o -~ ~ '~ ~ ~ ~A~ .~ O T~. -—I O ~ !_ 4_~ _ ~ . C~ ~ o o E~ o 1~ ~ ~ ~ _~ E~ ~ . . ~ ~ -~ ~ O ~ _o ~ o o ~ ~ o _ ~A~ E—l -~ Z ~ _ O E—I ~A~ E-l ~ -~ . IC, ~A~ U O _ ~ Z O ~ ~ O O ~ ~ 4~ 4~ ~ _ _I E~ __I ~ -~ ~A~ 4~ ~ _ _I ~, O ~ ~ O ~ ~A~ ~o O _~ ~ · ~ 4~ 0 o 4 ~ ~A~ ~ ·~ O O 4 ~ _~ ~ O ~ —~ ~ ~ ~ 4_ ., __I __I ~ ~ ~ _ _I ~ ~ ~ -g , O ~A~ ~ ~ ~ '~ ~ ~ ~ ,= ,= ~ ,_ _ _ - O ~ C~ C~ ~ ~ 4~ o __I o 4~ C) 0 ~ (1_ H 4~ ~ ~ O .~ ,~ O ~ ~A~ ~A~ .~ O O C) 4~ ~ ~ O 4~ ~ ~ 4~ ~ O O ~A, ~ ,~ _ _I O O !_ ~ ,= ~ ~ ~. _o O ~ ~ ~ ~ ~ O 0 4~ ~ ~ ~ ~ ~ O __I .~ ; O ~ ~ 4 0 4 ~A, O B~ ~A~ C) 4~ ~ ~ O ~A~ O 4~ 0 .~ ~ O ~ O __I ,= ~ O ~ C`' ~ _~ ~ O O~ C O >_ _ ~ _ O S ~ ~ O - ~ - S o -~ -~ O fL 4~ o 4~ O 4~ o ~A~ 4 4 4~ ~A~ _~ 11 _~ .~ o ~A~ 11 A _~ ~ _~ _ ~ Z ~ 4 ; :~s 11 ~ ~A~ A _4 ~ Z ~0 ~ ~ O V O o 11 E— - O Z ~

pRIM~E BODIES ~5 mission or set of missions will advar~e current knowledge regarding the key (paradigm-al~ring) questions. The magnitude of the advar~e is indicted by ~e number of ``x~s,' in ~ nonlinear fashion (i.~., xxx :> (xx + x)~. Similar rar~kings for different missions on ~ particular question do not imply scientific redundar~cy because the questions are multidimensional. llECOhlME - ATIONS OF THE PRIMITIVE BODIES PANEL TO THE STEERING GllOl}P In establishing ~ rar~ked list of missions for the continued exploration of primitive bodies' the parted took into account various factors relend to missions ~~ are technically fusible in ~e decade 2003-2013. The following factors were included: The paucity of radioisotope power systems currently available' The fwt ~~ no major new Ethnology developments were required, arid ~ The need for focused scientific objectives. The ranked mission set thy the Primitive Bodies Parted recommends is as follows: I. Kipper Belt-~toF~plorer. Such ~ mission cart be accommodated within the cost rar~ge of ~ medium-cl~s program. 2. Comet N~ Sops ~~. A mission of limited scope (e.g.' Comet Surface Sample Return} could be included in the medium-class cost Amatory. A larger-se ale mission win greater eapabilily (em., Comet Cryogenic Sample lectern) would fall into the category of ~ large mission. Depending on phasing, both are desirable. 3. Troj~Asmro`~C=~con~f''ss~. 4. Aswarm lope balm. S. Tr`to~ept=eFlyLy. FIEF Elf EN C ES 1. E.h4. Shoemaker Id C.S. Shoemaker' <<The Role of Collisior~> ire J.K. Be~> C.~. Pe~r~r~> Id A. Ch:~ikir~ ~ds.~> ~e New So~r ' Sky Publishir~g' Cambridge' harass.' ~ PPP' pp . ~ I-. 2. J.A. Wood' <<Origir1 of the Solar Sys~m>~' ir1 J.K. Be~' C.~. Pe~r~rl' Id A. Ch:~ikir1 ~ds.~> ~e New Sort Sky Publishirlg' Cambridge> h4~.> ~ ?? 9> pp . ~ 3-~. 3. J.~. Brawn' 1lOomets>~> ir1 J.K. Be~' C.~. Peter~rl' Id A. Chaikir1 ~ds.~' ~e A7ew Sort Sky Publishirlg' Cambridge' harass.' 1999> pp. 321-336. 4. C.R. Chapman) 1lAs~roids))) ire J.K. dewy) Cog. Peter~r~) Id A. Chaikir~ (eds.~) ~e New So~r~) Sky Puhlishir~g) Cawhrid~ harass.) 1999) pp. 337-350. S. D.P. Cruiksh~k) Traitor Pluto) Id Charor~)) ire J.K. dewy) Cog. Petersen) and A. Chaikir~ (eds.~) ~e New Sour ~~' Sky P~hli~hi~ C~mbricl~ Mn~ 1999. ~~ 985-~9FS ~ ~ 1 1 6. P.R. Weissm~) 11 Cometary Re~rvoirs)~) in J.K. dewy) Cog. Petersen) Id A. Chaikir~ ~ds.~) ~e N~ So~r~) Sky Publishing) Cawhrid~' h4~.' 1999' pp. SP-~. 7. J.W. Schopf) Cr~leoft~fe: ~e Discover of Ear~EarEe~tFo~) Prir~mton University Press) Prir~mtor~) N.J.) 2001. S. C.F. Chum) TV. Owerl) arid W.-H. Ip) Blimps Delivery of Volatile Id Organic Molecules to Eight) in T. Gehrels ~d.~) Awry Due to Comer carom Ur~iversi~ of Arizona Press) Tucson' 1994) pp. I-. ?. P. Ehrenfreur~d Id S.~. Chamley) 1lOrg~ic Molecules ire the Ir~r~ellar Medium) Comets) Id h<~orites: A Royal from Dark Cloudstothe Early Earth))' A~=lRwtews of Astro~o~ya~Astroph~38: 4~483) 2000. 10. Y.J. Perldletorl Id L.J. Allam~dola) Tithe Organic ~fr:~ctory Material ir1 the Diffuse ~ters~llar Medium: h~id-~frared Specko- scopic Corlskair~))) Atrophy Jour~upp~t 138: 75-~) 2002. 11. W.h4. Irvir~) F.P. Schloerb) J. Crovisier) B. Fegley Jr.) arid hi.J. hummer 1lOomets: A Link Between ~ter~ellar Id Nebular Chemistry))) ir1 V. hemmings' A.P. Boss) Id S.S. Russell (eds.~) Proto~r~ IMP W) Urliversity of Arizorl:~ Press' Tucsorl) 2000) pp. IS9-~200. 2. E. Griln) 1l~terpl~et~ Dun Id the Zodiacal Cloud))' ir1 P.R. Weissm~) L.-A. hi~Fad~) Id TV. Johrlsorl ~ds.~) Open of eSo~r~' Academic Press' Sari Diego) Calif.' 1999' pp. 673-~. ~ 3. J.I. Lur~ir~) TV. Owen) Id R.H. Prow) Tithe Outer Solar System: Chemical Cor~r:~irds ~ Low Temperatures ore Planet Form~ior~ ire V. h4~ings) A.P. Boss) Id S.S. Russell ~ds.~) Protos~rs a~P~ W) Ur~iversi~ of Arizona Press) Tucson) 2000) pp. 1055-1080.

HEW FR0~ IN =E SOLAR MOM 14. ~ A. Curds md S.A. S~m' ~lCollisior~ Rams in the Pre~rJ-~ Kuiper Be it arid centaur Regior~: Applications to Surfam A~iv~ior~ Ad h~odific~ior~ ore Comets' Kuiper Belt Objects' Cerdaurs' md Pluto-Charor~' Barn 145: 220-~' 2000. ~ S. D.T. Brig Ad L.A. Lebof~y' I<A~eroids>~> ~ P.R. Weissm~' L.-A. h4oF:~d~r~> arid T.~. Johnson ~ds.~' E~ope1~ of ~e Sour Amid Press, Son Diego' Calif.> 1999' pp. 585-605. 6. h4.E. Lip schutz md L. Schultz llh4~orites>~> in P.R. Weissm=' L.-A. h4oFad~r~' md T.~. Johnson ~ ds.~' E~ope~a of ~e Sour > Academic Press' Son Diego' Calif.' 1999> pp. 629-671. 17. P.R.Weissm~' 1lCometaryRe~rvoirs>~' inJ.K. Beauty' Cog. Peter~r~' ~dA. Chaikir~ ~ds.~' ~~So~r~' Sky Publishir~g' Cambridge' Ah. 1999' pp. An-. 18. D.~. Jewi~ Ad J.X. Luu' <Physical Nature of the Kuiper Belt>~> ire V. h4~ings' A.P. Boss' Ad S.S. Russell ~ds.~' Prom a PA W' Ur~iversi~ of Arizona Press' Tucson> 2000' pp. 1201-~. ?. E. GrOn' ll~terpl=et~ Dun Ad the Zodiacal Cloud>~' ire P.R. Weissm~' L.-A. h4oFad~' Ad T.~. Johr~sor~ ~ds.~' E~lope~a of Sort Academic Press' Sad Die go' Calif.> ~ ?~> pp . 673-6 96. 20. W.K. H~m~> I<Small Worlds: P~rr~s Ad ~l~ior~ships>~' ire J.K. Beady' C.~. Peter~r~' Ad A. Chaikir~ (eds.~> ~e H~ Sour ' Sky Publishing' Cambridge' Ah. ~ ?~' pp . 3 ~ ~ -320 . 21. h].J. Duress= ~ d J.J. Lissauer~ Molar System ~amics>~> ~ P.R. Weissm~> L.-A. h4oFad~r~~ Ad T.V. Johnson (eds.)~ E~lope~a of ~e Sort Academic Press' Say Diego, Calif.' 1999' pp. 809-~. 22. ~ . Hapke' I<Spam We~herir~g from Mercury to the Aneroid Belt>~' Journal of Mope Regears ~ 06: ~ 0039-~ 0074' Coo ~ . 23. h4.E. Zoler~sky' R.J. Bowler' E.K. Gibsor~ Jr.> L.E. Nyqui~' Y. Reese' C-Y Shih' Id H. Weism~' <1As~roida1 Wear Withm Fluid olusior~-~arir~g Halite in art HS Chor~dri~> hior~ahar~s ~ ~ ?~' $~e 285: ~ 377- ~ 379> ~ ?? ~ . At. F.J.h1. Rietmeijer'1l~rpl~etary~u~ Particles>~eralo~ 36: 2.~-~.~' 1998. 25. 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Solar system exploration is that grand human endeavor which reaches out through interplanetary space to discover the nature and origins of the system of planets in which we live and to learn whether life exists beyond Earth. It is an international enterprise involving scientists, engineers, managers, politicians, and others, sometimes working together and sometimes in competition, to open new frontiers of knowledge. It has a proud past, a productive present, and an auspicious future. This survey was requested by the National Aeronautics and Space Administration (NASA) to determine the contemporary nature of solar system exploration and why it remains a compelling activity today. A broad survey of the state of knowledge was requested. In addition NASA asked for the identifcation of the top-level scientific questions to guide its ongoing program and a prioritized list of the most promising avenues for flight investigations and supporting ground-based activities.

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