----------------- DRAFT ----------------06/26/2015
----------------- DRAFT ----------------First draft for SBAG community comment
Goal I: Science
Send comments to:
Dr. Tim Swindle
SBAG Goal I Lead
tswindle@lpl.arizona.edu
Comments due by:
09/19/2015
Also feel free to contact Dr. Nancy Chabot, SBAG chair:
Nancy.Chabot@jhuapl.edu
Goal I Subcommittee: T. Swindle (lead), K. Carroll, J. Castillo-Rogez, W. Grundy, E.
Kramer, J. Nuth, C. Raymond, H. Smith
----------------- DRAFT -----------------
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I.
Advance our Knowledge about the Solar System’s Formation and Evolution, as well as our
Knowledge about the Development of the Conditions Necessary for the Origin of Life, through
Research and Exploration of Small Bodies.
The small bodies now present in the Solar System represent remnants of the building blocks of
the planets. As such, they are our best windows into the processes that occurred during the
earliest history of the Solar System. But they also, as a result of their large numbers, represent
test particles that have survived 4.5 billion years of evolution of the Solar System, and bear the
results of many processes that have occurred during that evolution. From their orbital
characteristics to their chemical compositions and their interior structures, they contain myriad
clues to the history of the Solar System, often retaining information that the larger planets have
lost. They also contain clues to the history of the habitability of the planets, not only because
they have a common pre-solar and early nebular history, but also because the bombardment of
the planets by small bodies has been a significant part of the planets’ histories.
There are several different categories of “small bodies” in the Solar System that we consider,
but these groups are interrelated, and the boundaries are not always clear. Small bodies we
consider include: 1) Asteroids, remnants of terrestrial planet accretion that are found both in
the Main Belt and as Near-Earth Objects; 2) Comets, bodies that outgas volatiles as they pass
through the inner Solar System but that usually originate in the icy outer Solar System; 3) Outer
Solar System Planetesimals, primarily Kuiper Belt objects but also including the Centaurs and icy
small moons of outer planets that presumably originated in the Kuiper Belt; 4) Meteorites,
remnants of Near-Earth Objects that have collided with Earth, providing samples that can be
analyzed with laboratory instruments; 5) Phobos and Deimos, the enigmatic moons of Mars
whose origin is unclear, but which may be more closely related to asteroids than to the planet
they orbit; and 6) Dust, whose high surface-to-volume ratio makes it atypically bright through
telescopes and also makes it possible for a micrometer-sized object to be captured by Earth’s
atmosphere without being destroyed.
Scientific goals, most of which apply to more than one of these types of objects, are:
a. Understand the census and architecture of small bodies in the Solar System.
A critical part of understanding the history of the small bodies in the Solar System, and
hence the history of the Solar System itself, is understanding exactly what is present.
Size-frequency distributions, distributions of chemical and spectral properties of
astronomical objects, and distributions of properties of all sorts in laboratory samples
have to be known before they can be explained, but knowledge of the existence of
these bodies is a zeroth-order requirement.
i. Continue and enhance search programs for NEOs, MBAs, KBOs, Centaurs and other
small objects.
Because of their small sizes, small bodies are inherently difficult to even identify
with telescopes, much less study. Although the bright tails of comets mean that
they have been observed since antiquity, every other type of small body orbiting
in the solar system has been discovered via telescopes. Most of the discoveries
have been the result of systematic search programs, whether for near-Earth
objects, Kuiper Belt objects, or small moons of the outer Solar System planets.
Furthermore, since objects in different regions of the Solar System orbit at
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vastly different rates, the optimal search parameters for one type of object (e.g.,
Kuiper Belt objects) may be completely inapplicable for some other type (e.g.,
near-Earth objects).
ii. Find and characterize new kinds of samples of small bodies through meteorites,
micrometeorites, interplanetary dust, and returned samples from comets and
asteroids.
Laboratory analysis provides a level of detail that is inaccessible to studies using
telescopes or even spacecraft. However, the level of knowledge of the Solar
System that we can gain from laboratory analysis is limited by the samples
available. Hence, to fully understand the small bodies of the Solar System, we
need samples from as many different objects as we can acquire, including
meteorites of as many different types as possible, micrometeorites,
interplanetary dust, and samples from comets (of both silicate and icy
materials), asteroids, the martian moons, and as many other small bodies as
become accessible to spacecraft technology.
b. Use small bodies in the Solar System to understand the origin of the Solar System
i. Study the mineralogy and elemental and isotopic composition of small bodies
(through ground-based spectroscopy, spacecraft analyses, and returned samples,
and samples of meteoritic material) to constrain their origins.
One of the most fundamental properties of an object is its chemical
composition. Its chemical composition not only speaks to the processes involved
in its formation (for example, does it represent material that would have
condensed at high or low temperatures?) but also to the possible paths its
evolution may take (a body that forms with frozen volatiles may undergo
processes that will not happen on an object made of more refractory material).
Different modes of study lend themselves to different types of analysis.
Chemical compositions can be measured on a grain-by-grain basis for returned
samples or laboratory samples of meteorites or interplanetary dust, while
infrared spectroscopy is one of the most effective tools for telescopic
observation, even though what it really determines is mineralogy. Spacecraft,
meanwhile, can make direct elemental determinations with techniques like
gamma-ray spectroscopy, but without the spatially resolution of laboratory
samples, or can use techniques like infrared spectroscopy to make
measurements with higher spatial resolution than that of ground-based
telescopes, but often at the price of poorer spectral resolution.
ii. Determine the ages of events in the early Solar System, using meteorites and
returned samples.
Knowing what happened when is critical to understanding processes. At one
level, knowing the onset and durations of events, whether it is chondrule
formation, aqueous alteration, or impacts, constrains what processes might be
possible candidates. For example, what is the relation of chondrule formation to
the formation of calcium-aluminum-rich inclusions, in either time or space? How
does the distribution of impact ages for meteorites from Main Belt asteroids
compare to the distribution for samples from the Moon, and what does that say
about the dynamical processes at work?
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iii. Use the distribution of compositions and ages of small bodies in the Solar System to
make testable predictions about observable parameters in forming planetary
systems.
Is the Solar System typical or anomalous? One of the best ways to test is to
figure out what happened when in the early Solar System and then compare
that to what is seen in planetary systems that are currently forming around
other stars. Ironically, although it can be very difficult to observe planets around
other stars, small bodies, or, more accurately, the dust that they generate, can
be much easier to detect. If we know things like when most of the gas cleared
from the Solar System and how frequent collisions were, we can look at other
systems to see if the same behavior is exhibited.
c. Understand the dynamical evolution of the Solar System
i. Use experimental, theoretical and observational studies to understand the
processes that alter orbits, including the Yarkovsky Effect, resonances, planetary
encounters, planetary migration, and other effects.
Because of their sizes, the orbits of small bodies, particularly those that are in
heliocentric orbit, are affected by processes that may affect planetary-sized
bodies little, if at all. For example, the volatile jetting that can drive changes in
cometary orbits and the Yarkovsky Effect that can move small objects around
the inner Solar System are both processes that would be of no importance to
the orbital evolution of Earth or Mars, but are major factors in the current
architecture of the Solar System. On the other hand, the distribution of orbits
within the Main Asteroid Belt, the Kuiper Belt and the Oort Cloud probably all
reflect planetary migration, to some degree. Theoretical studies provide the
underpinning for understanding these processes, but these theoretical models
need to be tested, both by experiments (either at the laboratory level or by
spacecraft on actual small bodies) and by very high-precision measurements of
the short-term evolution of orbits of small bodies, particularly near-Earth
objects.
ii. Combine theoretical and observational studies to study the evolution of the
distribution of small bodies.
While there are many processes that could alter the orbits of small bodies, the
current architecture of the Solar System reflects one specific history. That
history, in turn, affects the planets, including Earth, both through impacts of
small bodies whose orbits were greatly perturbed, and through interactions
between the planets. Small bodies provide the best chance to fully understand
the history of planets like Earth and Mars. The Main Asteroid Belt, for example,
can be thought of as an ensemble of test particles, and the present architecture
of the Main Belt must be a reflection of the same history that the terrestrial
planets experienced.
iii. Use the surface ages of small bodies determined by studies of crater density,
surface morphology, spectral reflectance and other remote sensing techniques, and
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the cosmic-ray exposure ages of meteorites to determine the most recent
dynamical history of these objects.
Some of the effects that can alter the orbits of small bodies, most notably the
Yarkovsky Effect, can be large enough on short enough timescales that they can
be tested by simply following the orbits of specific objects with enough
precision. But other effects, including planetary resonances, close encounters
with planets, and even aspects of the Yarkovsky and YORP Effects occur on
longer timescales, or infrequently enough that we cannot directly observe them.
However, the recent orbital history of an object is recorded on the surface of
small bodies, as a result of the bombardment by meteoroids and
micrometeoroids and of solar and galactic charged particles, and even tidal
effects (during planetary encounters). Determining the extent to which all of
these secondary effects have occurred can provide constraints on the strength
and nature of the orbital processes.
iv. Use the observed distribution of small bodies in the Solar System to understand the
possible pathways of dynamical evolution in other planetary systems.
As our knowledge of other planetary systems explodes, so, too, do models of
the evolution of such systems. It is crucial to ask the question of what those
models would imply for the best-studied system we have, the Solar System. Just
as studies of the Solar System can lead to predictions that can be tested at other
planetary systems, so too can predictions based on observations from other
systems be tested on the Solar System.
d. Understand the evolution of small bodies’ surfaces and interiors, and the relationship to
other events and processes in the Solar System.
i. Understand the structure of the surfaces of the small bodies in various locations in
the solar system.
Our direct analysis of small bodies, whether via spacecraft, telescope or
laboratory analysis of samples, is generally limited to material that has been at
or near the surface of some body, at least in the most recent past. Therefore, it
is essential to understand the processes that affect the surfaces, particularly
those known as “space weathering,” and how they affect various properties.
However, these processes are also worthy of study in their own right.
ii. Understand the overall physical properties of small bodies and how they affect and
are affected by, the structure of interiors (including densities, porosities, and spin
rates).
Although most of our observations of small bodies deal with the surfaces, most
of the material composing those bodies is below the surface. To truly
understand those bodies, we need to understand the interiors, and whether the
surfaces are representative of the entire bodies, or whether there are significant
heterogeneities. While we cannot yet directly access the interiors, they
dominate properties such as density, porosity, and gravity, some of which can
be estimated from ground-based measurements or flybys, others of which could
be measured using geophysical techniques such as gravimetry and radar
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sounding. Many other properties, such as spin rate and, to the extent that it can
be determined, thermal history, are highly dependent on properties of the
interior.
iii. Combine theoretical models with observable results to determine the evolution of
the interiors of small bodies, including differentiation, metamorphism, and
fragmentation/reaccretion.
It is not enough to know what the interiors of small bodies are like at present –
we also need to know how their interiors have evolved to their current states.
Our analysis of the current interiors is necessarily limited, but we have bodies
that once were in the interiors of larger bodies, most notably differentiated
asteroids and meteorites. In addition, theoretical models of the interiors all
kinds of small bodies predict evolutionary paths that can be compared to the
current observed states.
iv. Determine the current and past magnetic fields of small bodies to understand
whether they possess remanent magnetism as a result of past core dynamos arising
from a magma ocean phase, or accretion of magnetized nebular material. This
includes both in situ analyses of small bodies via spacecraft and laboratory analyses
of meteorites and returned samples.
e. Determine the source, amount, and evolution of volatiles in small bodies in the Solar
System.
Life as we know it is based on volatile elements (such as C, N, H, O, and S) and
compounds (including water and organic molecules). In addition, the presence of
volatiles can alter the history of an object, altering minerals, causing outgassing that can
affect orbits, and even contributing to resurfacing. Also, volatiles in small bodies
represent potentially valuable extractable resources.
i. Measure volatiles (including, but not limited to, water, organics, other C-, N-, O- and
S-bearing species and noble gases) in asteroids, comets, KBOs, meteorites,
Phobos/Deimos and other small bodies.
A first-order goal is to understand the present distribution of volatiles in the
Solar System. Volatiles can be measured easily in laboratory samples using a
variety of high-precision techniques, although contamination is often a problem;
techniques such as neutron and gamma-ray spectroscopy can be used by
spacecraft to search for volatiles, and volatile compounds often have distinctive
spectral signatures, particularly in the IR, that can be used to detect them from
the ground. The early stages of contemplated asteroid-mining activities may
result in bulk extraction of volatiles, for example through excavation and
heating, which if analyzed during that stage of processing could provide
scientifically valuable composition estimates of uncontaminated samples.
ii. Compare the chemical and isotopic compositions of volatiles in different groups of
objects to understand the distribution of volatiles in the early Solar system.
We would like to know the present distribution of volatiles in the Solar System,
but to understand the origin and evolution of the Solar System, we also need to
understand what volatiles were present in small bodies at the beginning.
Isotopic measurements are crucial, since many processes that can cause volatile
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loss will also cause isotopic fractionation, particularly for volatiles that end up in
planetary atmospheres, such as the noble gases, carbon dioxide, nitrogen and
water, among others. Isotopes can be measured most precisely in the
laboratory, but some volatile compounds can be readily measured by groundbased telescopes if they are outgassed from a small body. Understanding the
relationship between the amount and isotopic compositions of various volatile
species in various types of small bodies should, in principle, make it possible to
piece together the initial Solar System inventory and composition of volatiles.
iii. Analyze the volatiles in meteorites, comets, or asteroids with different histories to
identify the processes altering volatile content after formation.
Even among objects that are basically similar, volatile contents can vary greatly.
Some meteorites are rich in hydrated materials, while others are almost
completely unequilibrated despite having volatiles present. Similarly, some
asteroid types have both hydrated and OH-free members. Gas-to-dust ratios
among comets vary widely. These are all providing clues to the processes that
occurred, but we need to find ways to decipher the clues, which requires, in
part, finding as many of the clues – obtaining as much data from distinct objects
and samples – as possible.
iv. Determine the amounts of volatiles that different groups of small bodies can deliver
to planets and moons in the Solar System.
Volatiles are crucial to the histories of planets and moons in the Solar System,
but their origin on these bodies is not necessarily well understood. As just one
example, the source of water on Earth remains controversial, but almost
certainly involves small bodies, whether in the form of late impactors or in the
small objects that accreted to become the Earth.
In the supplements that follow, we discuss these scientific goals as they apply to particular
objects or classes of objects, highlighting some of the major scientific questions at present, and
pointing out major missions, research programs, and facilities that are key to addressing the
scientific goals. We note that when we address missions, we explicitly limit ourselves to
discussion of New Frontiers-level missions. Discovery missions have been extremely successful
in addressing the questions surrounding small bodies, and we strongly endorse the continuation
of such missions, but do not wish to intervene in the historically-successful competitive selection
process by highlighting specific missions at that scale.
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Goal I Supplement A: Asteroids
Major Science Questions
(1) What is the compositional structure of the main asteroid belt today, and how has material migrated
from where it initially formed?
(2) What was the compositional gradient of the asteroid belt at the time of initial protoplanetary
accretion, and what was the redox and thermal state/gradient of the early solar system? How did
this affect planetary formation and evolution?
(3) What was the distribution of volatiles in the early solar system, and what role did asteroids play in
delivery of water and organics to the inner solar system?
(4) What are the characteristics of water-rich and/or hydrated asteroids and the role of hydrothermal
processes in formation of brines and organic material?
(5) What are the physical properties and key processes (e.g., differentiation, impact cratering, tectonics,
regolith development, and space weathering) on small bodies and how are they modified over time?
Planetary Mission Priorities
The Decadal Survey identified Trojan Tour as a candidate for the next New Frontiers mission. Missions to
investigate multiple main belt asteroids, and in particular, main belt comets, should be a priority for
future exploration. In-situ exploration and sample return, particularly from objects not well-represented
in the meteorite population, would expedite progress towards the science objectives espoused above.
Research and Analysis Contributions
Recent progress in modeling the dynamic evolution of the early solar system has yielded predictions of
the impact fluxes and compositional gradients that can be tested by missions to visit and map asteroids,
and to some extent telescopic data. Research on the physics and chemistry of ices has yielded important
inferences on the evolution of icy asteroids and their surfaces. Comprehensive models of the evolution
of small bodies, including thermal evolution, hydrothermal and low-temperature chemistry, and surface
processes are key to understanding how to interpret the properties we can measure and to understand
the possible habitats for life in this transitional region between the terrestrial planets and ice outer solar
system bodies.
Key Facilities and Programs
Ground-based facilities provide a wealth of data on the asteroid population and its characteristics,
including the Arecibo and Goldstone solar system radars, the Keck and IRTF telescopes on Mauna Kea
(Hawaii), Pan-STARRS, Catalina Sky Survey (CSS) and the impending Large Synoptic Survey Telescope
(LSST), and well as an international network of smaller telescopes. The Minor Planet Center and the JPL
NEO office record, track and catalog the asteroid population and support planetary defense
assessments. The Hubble Space Telescope and Spitzer Observatory also provide unique and valuable
data on small bodies in the main belt. The Antarctic Search for Meteorites is the largest source of
diverse extraterrestrial materials to support solar system studies.
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Goal I Supplement B: Comets
Major Science Questions
(1) What is the interior structure of comets? How does that structure evolve as the comet undergoes
thermal evolution?
(2) What is the size distribution of comets? Do the different dynamical subclasses have different
distributions?
(3) What are the drivers of cometary activity? Does the nature of cometary activity depend on the
activity driver?
(4) What is the life cycle of a comet as it is perturbed in to the inner solar system? That is, how do
Centaurs become comets? What fraction? For how long do comets survive once they are perturbed
into the inner solar system?
(5) What is the nature of volatiles in comets? What is the Deuterium to Hydrogen ratio of the different
comet populations?
Planetary Mission Priorities
The Decadal Survey identified the Comet Surface Sample Return mission as a top candidate among
future New Frontiers missions. While the material collected in the Stardust mission has provided a
wealth of insights, the volume of material collected was small, and the high velocity collection technique
altered the particles from their original form. A mission that returns a much larger sample of material
from the surface of a comet would likely revolutionize our understanding of primitive bodies.
ESA’s Rosetta mission is already providing a wealth of new information, and will continue to do so as
67P/Churymov-Gerasimenko approaches perihelion.
Research and Analysis Contributions
The use of publicly available archival data is extremely important to long-term characterization of shortperiod comets, as well as population-wide studies of long-period comets. Ongoing analysis of these
data, as funded by R&A programs, helps to leverage additional insights from data already collected by
both ground-based and space-based facilities. Additionally, the continued collection of high-quality data
on new or returning comets is critical, due to the ever-evolving nature of comets.
Key Facilities and Programs
There are several key facilities and programs that contribute to cometary science. The IRFT is a critically
important facility for cometary study, used to identify surface properties and characteristics, finding the
existence of CO and PAHs in comet spectra. Radar observations with Arecibo allow the physical size and
dimensions of comets to be measured, which may lead to insights in cometary activity and evolution.
Publicly available archival data sets, especially those from surveys (e.g., NEAT, NEOWISE, Spitzer, CFHT),
help to characterize long-term cometary behavior. Making more data sets publicly available and easily
searchable would contribute substantially to the understanding of cometary behavior.
In the coming years, ALMA will provide exceptional data at wavelengths that have not been explored,
allowing the study of difficult to observe emission lines such as those from CO and PAHs.
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Goal I Supplement C: Meteorites
Major Science Questions:
(1) What were the conditions under which the earliest solids in the Solar System formed? Objects like
chondrules and calcium-aluminum-rich inclusions (CAIs) clearly reflect high-temperature events, but
what were those events, and how much mixing occurred after formation?
(2) What was the contribution of surviving pre-solar solids? What fraction of material in different
primitive meteorite groups came from what pre-solar environments?
(3) What was the timeline in the earliest Solar System? Relative to CAIs, when did chondrules form and
did their formation overlap that of CAIs? When did chondrites accrete, and how does that compare
in time with the differentiation of the parent bodies of iron meteorites? When did aqueous
alteration of chondrites start, and how long did it progress?
(4) What groups of meteorites correspond to what types of asteroids and/or comets?
(5) What kinds of organics materials are contained in what groups of meteorites? How does the
abundance and distribution of organic materials depend on the history of individual meteorites?
Were those organics synthesized within the solar nebula or on meteorite parent bodies, or were
they synthesized elsewhere and survived in the nebula long enough to be incorporated?
Planetary Mission Priorities:
The community of scientists who study meteorites and interplanetary dust has a near-complete overlap
with the community that studies samples returned by missions from Apollo onward. These missions, and
upcoming sample-return missions, such as OSIRIS-REx and the proposed New Frontiers Comet Surface
Sample Return mission, provide the context of a known parent body, a key piece of information, as well
as providing samples that have not suffered through atmospheric entry.
Research and Analysis Contributions:
The meteorite community is funded almost entirely through R&A programs, so these programs,
including programs to establish and maintain expensive state-of-the-art analytical facilities, are crucial
to progress in this area.
Key Facilities and Programs:
The Antarctic Search for Meteorites (ANSMET) is crucial to meteorite studies. Although collectors find
comparable numbers of meteorites elsewhere, the ANSMET collection represents an unbiased collection
of an area, with well-documented collection circumstances, minimal contamination, and maximum
accessibility to researchers. Collection programs like ANSMET are particularly crucial for identifying new
groups of relatively rare meteorites.
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Goal I supplement D: Phobos and Deimos
Major Scientific Questions:
(1) What are the martian moons composed of? What is the elemental and chemical composition of
Phobos and Deimos? What are the spectral features on Phobos? Are volatiles (i.e.water) present?
Does the composition of the martian moons differ from one another and from Mars?
(2) What are the physical and surface properties of Phobos and Deimos? What is the internal structure
of each of the martian moons? What physical (geology) processes occur (or have occurred) on the
martian moons (weathering, impacts, tidal evolution, groove formation, etc.)? Is the redder unit of
Phobos weathered ultramafic material from Mars or transferred material from Deimos?
(3) What is the origin of Phobos and Deimos? Are they related to primitive/ ultra-primitive D-type
asteroids? Are Phobos and Deimos formed from re-accreted Mars ejecta? Are Phobos and Deimos
captured bodies formed elsewhere in the Solar System? If a captured body, where did they
originate (the asteroid belt, outer main belt, Kuiper Belt, etc.)? Do the two martian moons have the
same origin?
(4) How do Phobos and Deimos relate to processes currently or formerly occurring on other bodies in
the Solar System? Are Phobos and Deimos similar to the sources of water and other volatiles
delivered to terrestrial planets in the early Solar System? Are surface processes on Phobos and
Deimos similar to those on S-type and C-type bodies? How does the origin and formation of Phobos
and Deimos relate to Mars?
Planetary Mission Priorities
Although not specifically targeted at Phobos and Deimos the New Frontiers candidate missions for Comet
Surface Sample Return and Trojan Tour and Rendezvous would contribute to a better understanding of
primitive bodies and surface processes on Phobos and Deimos.
Research and Analysis Contributions
The majority of Phobos and Deimos research is funded through the research and analysis program
within the Planetary Science Division. These NRA’s include: Solar System Workings, Mars Data Analysis,
and Emerging Worlds.
Key Facilities and Programs
Key facilities for investigating Phobos and Deimos are spacecraft orbiting Mars (MRO, Mars Express,
Odyssey, MAVEN, MSL, MER) and The Hubble Space Telescope. The Solar System Exploration Research
Virtual Institute (SSERVI) is a vital program for Phobos and Deimos investigations.
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Goal I Supplement E: Outer Solar System Planetesimals
Major Science Questions
(1) Where in the protoplanetary nebula did the various remnant populations of outer solar system small
bodies form, and what can they reveal about the distinct conditions in nebular regions as
planetesimals accreted and merged into larger bodies? Studies of small bodies can help address
many sub-questions on the protoplanetary nebula, including: How does accretion proceed through
various size regimes? What are the effects of “snow” lines (including volatiles other than H2O)? What
is the extent of radial and vertical mixing? What is the role of pre-solar solids inherited from the
molecular cloud? What chemical processing occurred in various nebular environments?
(2) Subsequent to the initial formation of outer solar system small bodies, what processes altered
objects in specific environments or the population as a whole? Small bodies studies can shed light on
a great variety of processes, including: What is the dynamical evolution of planetesimal and giant
planet orbits, and of binaries and multiples? What is the role of short half-life radionuclides in driving
early internal heating? How do internal volatile transport, compaction, differentiation, and loss of
volatiles to space occur? What is the effect of impacts by dust and larger projectiles? What is the
history of collisional fragmentation and production of dust and comet nuclei? How does the chemical
evolution of complex organics occur inside and on the surfaces of small planetesimals, via radiolysis,
photolysis, and chemical processes that act over long time scales?
Planetary Mission Priorities
NASA's New Horizons mission visits the Pluto system in 2015. Pluto is among the largest Kuiper belt
objects, with a complex satellite system thought to result from a giant impact. Its atmosphere, seasonal
volatile transport cycles, and other size-dependent features will shape our thinking about other large
Kuiper belt objects. An extended mission could explore a small, undifferentiated Kuiper belt object.
Bookending the size distribution by exploring both a planet-sized body and a small planetesimal is an
exciting prospect for Kuiper belt science, and is strongly supported by the community.
The latest Planetary Decadal report recommended no new starts for Kuiper belt exploration in the larger
mission size classes. But of the New Frontiers recommendations, both the Comet Surface Sample
Return and the Trojan Tour are valuable to Kuiper Belt science. The first would return a sample from an
object that formed as an outer solar system planetesimal (albeit only the refractory components). The
second would survey a sample of those planetesimals trapped into Trojan-type orbits 5 AU from the
Sun, where they would be less thermally processed than objects in the main asteroid belt (albeit much
more thermally processed than their siblings in the Kuiper belt). It could also be possible to encounter a
Centaur on the way to Uranus, shedding light on how Kuiper belt objects evolve as they transition to
cometary orbits.
Two flagship class missions in NASA's Astrophysics Division are especially important for outer solar
system small bodies science. Hubble Space Telescope has made many important discoveries in this field
over the past quarter-century, and James Webb Space Telescope is also expected to play a significant
role when it becomes operational.
Research and Analysis Contributions
Dynamical modeling, informed by observed orbital distributions of outer solar system small bodies, has
completely reshaped our view of the early evolution of the solar system. Continuation of this work is
crucial for refining the details of that history via observationally testable predictions and also for linking
present-day small body remnant populations to their places of origin in the protoplanetary nebula,
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enabling their use to study distinct nebular environments. Dynamical modeling needs to be well
supported in the R&A program portfolio, and it needs to be clear what portion of the program (Solar
System Workings? Emerging Worlds?) will be supporting it.
Modeling the mechanical and thermal evolution of planetesimals and the mobility of volatiles within
them is crucial for understanding how the objects available for study today relate to those that formed
in various regions across the protoplanetary nebula.
Further laboratory studies are needed on the fundamental properties of cryogenic materials, as well as
low temperature chemistry occurring over very long timescales and the effects of various types of
energetic radiation.
Key Facilities and Programs
Being small and distant, Kuiper belt objects are especially faint and challenging observational targets.
Their study depends on access to the most capable telescopes: Hubble, JWST, Keck, ALMA, Spitzer, etc.,
and can benefit from future facilities currently under construction or still in planning stages. Support for
observational studies is at present mostly through the SSO program.
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