National Academy of Sciences
National Academy of Engineering
Institute of Medicine
National Research Council
Office of Congressional and government Affairs
At A Glance
: Threat of Near-Earth Asteroids
: 10/03/2002
Session: 107th Congress (Second Session)
: Joseph A. Burns

Irving Porter Church Professor of Engineering and Professor of Astronomy, Cornell University and Member, Solar System Exploration Survey Committee, National Research Council, The National Academies

: House
: Committee on Science


Statement of

Joseph A. Burns, Ph.D.
Member of the Solar System Exploration Survey Committee
National Research Council/The National Academies
Irving Porter Church Professor of Engineering and Professor of Astronomy
Cornell University

before the

Subcommittee on Space and Aeronautics
Committee on Science
U.S. House of Representatives

OCTOBER 3, 2002


Mr. Chairman, Ranking Minority Member, and members of the subcommittee: thank you for inviting me to testify on behalf of the National Academies’ Solar System Exploration Survey. My name is Joseph Burns, and I am Irving Porter Church Professor of Engineering and Professor of Astronomy at Cornell University. I appear today in my capacity as a steering group member of the Solar System Exploration (SSE) Survey, and as a former chair of the National Research Council’s Committee on Planetary and Lunar Exploration (COMPLEX). I was also a member of the Astronomy & Astrophysics Survey’s panel on Ultraviolet and Infrared Astronomy from Space.

As you know, the Astronomy and Astrophysics community has a long history of creating, through the National Research Council (NRC), decadal surveys of their field. These surveys lay out the community’s research goals for the next decade, identify key questions that need to be answered, and propose new facilities with which to conduct this fundamental research.

In April 2001, NASA Associate Administrator for Space Science Edward Weiler asked the NRC to conduct a similar survey for planetary exploration. Our report, New Frontiers in the Solar System, is the result of that activity. The Solar System Exploration Survey was conducted by an ad hoc committee of the Space Studies Board (SSB), overseen by COMPLEX. This committee was comprised of some 50 scientists, drawn from a diverse set of institutions, research areas, and backgrounds; it also received input from more than 300 colleagues. The SSE Survey had four subpanels which focused on issues pertaining to different types of solar system bodies (Inner Planets, Giant Planets, Large Satellites, and Primitive Bodies) and received direct input from COMPLEX on Mars issues and from the Committee on the Origins and Evolution of Life on issues pertaining to Astrobiology.

New Frontiers in the Solar System (the Executive Summary is appended to this statement) recommends a scientific and exploration strategy for NASA’s Office of Space Science that will both enable dramatic new discoveries in this decade and position the agency to continue to make such discoveries well into the future. Your invitation indicated that I should focus on the conclusions that the SSE Survey reached in the area of Near-Earth Objects (NEOs).

Near-Earth Objects

The SSE Survey’s charge from NASA included a request to summarize the extent of our current understanding of the solar system. This task was delegated to the subpanels, which in the particular case of NEOs was handled by the Primitive Bodies Panel.

Scientifically, the history of impacts on the Earth is vital for understanding how the planet evolved and how life arose. For example, it has been suggested that a majority of the water on this planet was delivered by comet impacts. A better known example of the role of impacts is the Cretaceous-Tertiary event that led to global mass extinctions, including that of the dinosaurs. Another case is the 20 megaton (MT) equivalent-energy explosion that devastated 2000 square-kilometers of pine forest in the Siberian tundra in 1908. The SSE Survey identifies the exploration of the terrestrial space environment with regards to potential hazards as a new goal for the nation’s solar system exploration enterprise.

Current surveys have identified an estimated 50 percent of NEOs that have a diameter of 1 kilometer or greater and approximately 10-15 percent of objects between 0.5 and 1 km. The vast majority of these latter objects have yet to be discovered, but a statistical analysis indicates a 1% probability of impact by a 300-m body in the next century. Such an object would deliver 1000 MT of energy, cause regional devastation, and (assuming an average of 10 people per square-kilometer on Earth) result in 100,000 fatalities. The damage caused by an impact near a city or into a coastal ocean would be orders of magnitude higher. As of a year ago, 340 objects larger than a kilometer had been catalogued as Potentially Hazardous Asteroids. In addition, the number of undiscovered comets with impact potential is large and unknown.

The Primitive Bodies panel went on to state:

“Important scientific goals are associated with the NEO populations, including their origin, fragmentation and dynamical histories, and compositions and differentiation. These and other scientific issues are also vital to the mitigation of the impact hazard (emphasis added), as methods of deflection of objects potentially on course for an impact with Earth are explored. Information especially relevant to hazard mitigation includes knowledge of the internal structures of near-Earth asteroids and comets, their degree of fracture and the presence of large core pieces, the fractal dimensions of their structures, and their degree of cohesion or friction.”

While almost all of the SSE Survey’s recommendations involved NASA flight missions, the Primitive Bodies subpanel recommended that ground-based telescopes be used to do a majority of the study of NEOs, supplemented by airborne and orbital telescopes.

A survey for NEOs demands an exacting observational strategy. To locate NEOs as small as 300 m requires a survey down to 24th magnitude (16 million times fainter than the feeblest stars that are visible to the naked eye). If images are to be taken every 10 sec to allow the sky to be studied often, the necessary capability is almost 100 times better than that of existing survey telescopes. NEOs spend only a fraction of each orbit in Earth’s neighborhood, where they are most easily seen. Repeated observations over a decade would be required to explore the full volume of space populated by these objects. Such a survey would identify several hundred NEOs per night and obtain astrometric (positional) measurements on the much larger (and growing) number of NEOs that it had already discovered. Precise astrometry is needed to determine the orbital parameters of the NEOs and to assign a hazard assessment to each object. Astrometry at monthly intervals would ensure against losing track of these fast-moving objects in the months and years after discovery.

Large-aperture Synoptic Survey Telescope

In its most recent decadal survey, the Astronomy and Astrophysics community selected the proposed Large-aperture Synoptic Survey Telescope (LSST) as their third major ground-based priority. In addition, our SSE Survey chose LSST to be its top-ranked ground-based facility. Telescopes like HST and Keck peer at selected, very localized regions of the sky or study individual sources with high sensitivity. However, another type of telescope is needed to survey the entire sky relatively quickly, so that periodic maps can be constructed that will reveal not only the positions of target sources, but their time variability as well. The Large-aperture Synoptic Survey Telescope is a 6.5-m-effective-diameter, very wide field (~3 deg) telescope that will produce a digital map of the visible sky every week. For this type of survey observation, the LSST will be a hundred times more powerful than the Keck telescopes, the world’s largest at present. Not only will LSST carry out an optical survey of the sky far deeper than any previous survey, but also –just as importantly-- it will also add the new dimension of time and thereby open up a new realm of discovery. By surveying the sky each month for over a decade, LSST would revolutionize our understanding of various topics in astronomy concerning objects whose brightnesses vary on time scales of days to years. NEOs, which drift across a largely unchanging sky, are easily identified. The LSST could locate 90 percent of all-near-Earth objects down to 300 m in size, enable computations of their orbits, and permit assessment of their threat to Earth. In addition, this facility could be used to discover and track objects in the Kuiper Belt, a largely unexplored, primordial component of our solar system. It would discover and monitor a wide variety of variable objects, such as the optical afterglows of gamma-ray bursts. In addition, it would find approximately 100,000 supernovae per year, and be useful for many other cosmological observations.

The detectors of choice for the temporal monitoring tasks would be thinned charge-coupled devices (CCDs); the requisite extrapolation from existing systems should constitute only a small technological risk. An infrared capability of a comparably wide field would be considerably more challenging but could evolve as the second phase of the telescope’s operation. Instrumentation for LSST would be an ideal way to involve independent observatories with this basically public facility.

NASA/NSF Cooperation

Historically, the National Science Foundation (NSF) has built and operated ground-based telescopes, whereas NASA has done the same for space-based observatories. Although the Astronomy and Astrophysics Survey was noncommittal on who should build the LSST, the SSE Survey included a recommendation that NASA share equally with NSF in the telescope’s construction and operations costs.

Such an arrangement has precedent. The SSE Survey noted that

“NASA continues to play a major role in supporting the use of Earth-based optical telescopes for planetary studies. It funds the complete operations of the IRTF (InfraRed Telescope Facility), a 3-m diameter telescope located on Hawaii’s Mauna Kea. In return for access to 50 percent of the observing time for non-solar-system observations, the NSF supports the development of IRTF’s instrumentation. This telescope has provided vital data in support of flight missions and will continue to do so. As another example, NASA currently buys one-sixth of the observing time on the privately operated Keck 10-m telescopes. This time was purchased to test interferometric techniques in support of future spaceflight missions such as SIM (Space Interferometry Mission) and TPF (Terrestrial Planet Finder).”

The solar system exploration community is concerned that the NSF is often unwilling to fund solar system research. This is particularly unfortunate given NSF’s charter to support the best science and its leadership role in other aspects of ground-based astronomy.

The shared responsibility between NASA and the NSF that we recommend is also endorsed by the more general findings last year of the NRC’s Committee on the Organization and Management of Research in Astronomy and Astrophysics (COMRAA), chaired by Norman Augustine. COMRAA’s report recommended that NASA continue to “support critical ground-based facilities and scientifically enabling precursor and follow-up observations that are essential to the success of space missions.” COMRAA also noted that in 1980 the NSF provided most of the research grants in astronomy and astrophysics, but today NASA is the major supporter of such research.

The roles of the agencies also affect the ability of scientists to conduct a census of Near-Earth Objects. The SSE Survey commented that:

“interestingly enough, NASA has no systematic survey-capability to discover the population distribution of the solar-system bodies. To do this, NASA relies on research grants to individual observers who must gain access to their own facilities. The large NEOs are being efficiently discovered using small telescopes for which NASA provides instrumentation funding, but all the other solar system populations—e.g., comets, Centaurs, satellites of the outer planets, and Kuiper Belt Objects—are being characterized almost entirely using non-NASA facilities. This is a major deficiency…”

The construction of the LSST would provide a central, federally sponsored location for such research.

LSST Costs and Survey Below 300 Meters

The costs of the LSST are projected by the 2001 Astronomy and Astrophysics Survey as being $83 million for capital construction and $42 million for data processing and distribution for 5 years of operation, for a total cost of $125 million. Routine operating costs, including a technical and support staff of 20 people, are estimated at approximately $3 million per year. The LSST will be able to routinely discover and characterize NEOs down to 300 m in diameter. Increasing the sensitivity of the survey to 100 m would mean increasing the sensitivity of the telescope by a factor of ten. This may represent a "beyond the state-of-the-art" challenge to telescope builder, and certainly a much larger telescope - 3 times the LSST and probably 10 to 100 times the cost unless innovative designs are found. The number of discovered objects would correspondingly increase substantially; this large data set may challenge current capabilities.

Concluding Thoughts

By way of summary, let me place the LSST into the context of a robust scientific program. Systematically building an inventory of the Near-Earth Objects is crucial to an improved understanding of Earth’s environment, especially to the prediction of future hazards posed to our species. It is also a necessary first step towards a rational program of NASA’s exploration of these bodies with spacecraft: many of the most interesting targets may remain, as yet, undiscovered. The ability to create and play a “motion picture” of the night sky will also provide new insights in a wide variety of disciplines from cosmology to astrophysics to solar system exploration. A suitable analog might be the deepened knowledge that is obtained from dynamic movies of swirling clouds and weather patterns, as compared to an occasional static photo.

The immense volume of data from the LSST would provide a reservoir of information for numerous graduate students and researchers, as well as established scientists. Further, LSST will support flight missions – for example, identifying possible fly-by targets for a spacecraft mission to explore the Kuiper Belt. All in all, the SSE Survey committee believes that broad areas of planetary science, particularly NEO studies, would benefit very substantially from the construction of the LSST for a relatively small investment.

Thank you again, Mr. Chairman, for the opportunity to appear before the subcommittee today. I would be glad to answer any questions that you or your subcommittee members may have.


Joseph A. Burns is the I.P.Church Professor of Engineering and Astronomy at Cornell University, where most of his professional life has been spent. He is a member of the Steering Committee of the just-completed Solar System Exploration Decadal Survey of the National Research Council; in the mid-1990s he had chaired a similar survey. He also served on one of the panels for the Astronomy and Astrophysics Decadal Survey (2000). His areas of research are planetary dynamics and the solar system’s structure. Burns is a member of three spacecraft imaging teams. Using ground-based telescopes and spacecraft, his students have discovered several planetary rings and about twenty small satellites of the giant planets.

Starting in the late 1970s Burns edited Icarus, the principal journal of planetary science, for about twenty years. He is presently is a Reviewing Editor of the journal Science. Burns is a Vice President of the American Astronomical Society and he has led its Divisions of Planetary Science (DPS) and on Dynamical Astronomy. He is a fellow of the American Geophysical Union and the American Association for the Advancement of Science, as well as a member of the Russian Academy of Sciences and the International Academy of Astronautics. Burns holds the USSR’s Schmidt Medal and the DPS’ Masursky Prize as well as three NASA medals for scientific achievement.


New Frontiers in the Solar System

Executive Summary

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.

Solar system exploration is a compelling activity. It places within our grasp answers to basic questions of profound human interest: Are we alone? Where did we come from? What is our destiny? Further, it leads to the creation of knowledge that will improve the human condition. Mars and icy satellite explorations may soon provide an answer to the first of these questions. Exploration of comets, primitive asteroids, and Kuiper Belt objects may have much to say about the second. Surveys of near-Earth objects and further exploration of planetary atmospheres will say something about the third. Finally, explorations of all planetary environments will result in a much-improved understanding of the natural processes that shape the world in which we live.

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 identification 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. To accomplish this task, the Solar System Exploration Survey’s (SSE Survey’s) Steering Group and panels have worked with scientists, professional societies, NASA and National Science Foundation (NSF) officials, people at government and private laboratories, and members of the interested public. The remarkable breadth and diversity in the subject are evident in the panel reports that are contained in Part One of this survey. Together they strongly reinforce the idea that a high-level integration of the goals, ideas, and requirements that exist in the community is essential if a practical exploration strategy for the next decade is to emerge. Such an integrated strategy is the objective of Part Two.


Based on the material presented in Part One of this report, the SSE Survey has identified four recurring issues, or crosscutting themes, that form an appropriate basis for an integrated strategy that can be realized by a series of missions to be flown over the next decade. The four crosscutting themes are as follows:

1. The First Billion Years of Solar System History. This first theme covers the formative period that features the initial accretion and development of Earth and its sibling planets, including the emergence of life on our globe. This pivotal epoch in the solar system's history is only dimly glimpsed at present.

2. Volatiles and Organics: The Stuff of Life. The second theme addresses the reality that life requires organic materials and volatiles, notably, liquid water. These materials originally condensed in the outer reaches of the solar nebula and were later delivered to the planets aboard organic-rich comets and asteroids.

3. The Origin and Evolution of Habitable Worlds. The third theme recognizes that our concept of the “habitable zone” has been overturned, and greatly broadened, by recent findings on Earth and elsewhere throughout our galaxy. Taking inventory of our planetary neighborhood will help to trace the evolutionary paths of the other planets and the eventual fate of our own.

4. Processes: How Planetary Systems Work. The fourth theme seeks deeper understanding of the fundamental mechanisms operating in the solar system today. Comprehending such processes—and how they apply to planetary bodies—is the keystone of planetary science. This will provide deep insight into the evolution of all the worlds within the solar system and of the multitude of planets being discovered around other stars.

Devolving from these four crosscutting themes are 12 key scientific questions. These are shown in Table ES.1, together with the names of the facilities and missions recommended as the most appropriate activities to address these questions. The priority and measurement objectives of these various projects are summarized in the next section.


Progress on the tabulated scientific themes and key questions will require a series of spaceflights and supporting Earth-based activities. It is crucial to maintain a mix of mission sizes and complexities in order to balance available resources against potential schemes for implementation. For example, certain aspects of the key science questions can be met through focused and cost-effective Discovery missions (<$325 million), while other high-priority science issues will require larger, more capable projects, to be called New Frontiers. About once per decade, Flagship missions (>$650 million) will be necessary for sample return or comprehensive investigations of particularly worthy targets. Some future endeavors are so vast in scope or so difficult (e.g., sample return from Mars) that no single nation acting alone may be willing to allocate all of the resources necessary to accomplish them, and the SSE Survey recommends that NASA encourage and continue to pursue cooperative programs with other nations. Not only is the investigation of our celestial neighborhood inherently an international venture, but the U.S. Solar System Exploration program will also benefit programmatically and scientifically from such joint ventures.

Discovery missions are reserved for innovative and competitively procured projects responsive to new findings beyond the nation’s long-term strategy. Such missions can satisfy many of the objectives identified in Part One by the individual panels. Given Discovery’s highly successful start, the SSE Survey endorses the continuation of this program, which relies on principal-investigator leadership and competition to obtain the greatest science return within a cost cap. A flight rate of no less than one launch every 18 months is recommended.

Particularly critical in this strategy is the initiation of New Frontiers, a line of medium-class, principal-investigator-led missions as proposed in the President’s fiscal year (FY) 2003 budget. The SSE Survey strongly endorses the New Frontiers initiative. These spacecraft should be competitively procured and should have flights every 2 or 3 years, with the total cost capped at approximately twice that of a Discovery mission. Target selection should be guided by the list in this report.

Experience has shown that large missions, which enable detailed, extended, and scientifically multifaceted observations, are an essential element of the mission mix. They allow the comprehensive exploration of science targets of extraordinarily high interest. Comparable past missions have included Viking, Voyager, Galileo, and Cassini-Huygens. The SSE Survey recommends that Flagship (>$650 million) missions be developed and flown at a rate of about one per decade. In addition, for large missions of such inclusive scientific breadth, a broad cross section of the community should be involved in the early planning stages.

Programmatic efficiencies are often gained by extending operational flights beyond their nominal lifetimes. Current candidates for continuation include Cassini, projects in the Mars Exploration Program, and several Discovery flights. The SSE Survey supports the current Senior Review process for deciding the scientific merits of a proposed mission extension and recommends that early planning be done to provide adequate funding of mission extensions, particularly Flagship missions and missions with international partners.

Because resources are finite, the SSE Survey prioritized all new flight missions within each category along with any associated activities. To assess priorities in the selection of particular missions, it used the following criteria: scientific merit, “opportunity,” and technological readiness. Scientific merit was measured by judging whether a project has the possibility of creating or changing a paradigm and whether the new knowledge that it produces will have a pivotal effect on the direction of future research, and, finally, on the SSE Survey’s appraisal of how that knowledge would substantially strengthen the factual base of current understanding.

Because of wide differences in mission scope and the diverse circumstances of implementation, the SSE Survey, at NASA’s request, prioritized only within three cost classes: small (< $325 million), medium ($325 million to $650 million), and large (> $650 million). Also, since the Mars Exploration Program line is already successfully established as a separate entity within NASA, its missions are prioritized separately in this report.

The recommendations from the SSE Survey’s panels have been integrated with the Solar System Exploration program’s overall goals and key questions in order to arrive at the flight-mission priorities listed in Table ES.2. The SSE Survey has included five New Frontiers missions in its priority list, recognizing that not all might be affordable within the constraints of the budgets available over the next decade.

Recommended Solar System Flight Missions (non-Mars)

Europa Geophysical Explorer

The Europa Geophysical Explorer (EGE), a Flagship mission, will investigate the probable subsurface ocean of Europa and its overlying ice shell as the critical first step in understanding the potential habitability of icy satellites. While orbiting Europa, EGE will employ gravity and altimetry measurements of Europa's tidal fluctuations to define the properties of any interior ocean and characterize the satellite's ice shell. Additional remote-sensing observations will examine the three-dimensional distribution of subsurface liquid water; elucidate the formation of surface features, including sites of current or recent activity; and identify and map surface composition, with emphasis on compounds of astrobiological interest. Prior to Europa-orbit insertion, EGE’s instruments will scrutinize Ganymede and Callisto, moons that also may have subsurface oceans, thereby illuminating Europa's planetary and astrobiological context. Europa’s thorough reconnaissance is a stepping-stone toward understanding the astrobiological potential of all icy satellites and will pave the way for future landings on this intriguing object.

Kuiper Belt-Pluto Explorer

The Kuiper Belt-Pluto Explorer (KBP) will be the first spacecraft dispatched for scientific measurements within this remote, entirely unexplored outer half of the solar system. KBP will fly past Pluto-Charon and continue on to do reconnaissance of several additional Kuiper Belt objects (KBOs). KBP’s value increases as it observes more KBOs and investigates the diversity of their properties. This region should be home for the most primitive material in the solar system. KBP will address the prospect that KBOs have played a role in importing basic volatiles and molecular stock to the inner solar system, where habitable environments were created. The SSE Survey anticipates that the information returned from this mission might lead to a new paradigm for the origin and evolution of these objects and their significance in the evolution of objects in other parts of the solar system.

South Pole-Aitken Basin Sample Return

The South Pole-Aitken Basin Sample Return (SPA-SR) mission will return samples from the Moon in order to constrain the early impact history of the inner solar system and to comprehend the nature of the Moon’s upper mantle. The South Pole-Aitken Basin, the largest impact structure known in the solar system, penetrates through the lunar crust. It is stratigraphically the oldest and deepest impact feature preserved on the Moon. The SPA-SR mission will help determine the nature of the differentiation of terrestrial planets and provide insight into the very early history of the Earth-Moon system. SPA-SR will also enable the development of sample acquisition, handling, and return technologies to be applied on other future missions.

Jupiter Polar Orbiter with Probes

The Jupiter Polar Orbiter with Probes (JPOP) mission will determine if Jupiter has a central core, a key issue that should decide between the two competing scenarios for the planet’s origin. It will measure water abundance, which plays a pivotal role in understanding giant planet formation. This parameter indicates how volatiles (H2O, CH4, NH3, and H2S) were incorporated in the giant planets and, more specifically, the degree to which volatiles were transported from beyond Neptune to the inner solar system. The mission will probe the planet’s deep winds to at least the 100-bar pressure level and may lead to an explanation of the extreme stability of the cloud-top weather systems. From its cloud-skimming orbit, JPOP will investigate the fine structure of the planet’s magnetic field, providing information on how its internal dynamo works. Lastly, the spacecraft will repeatedly visit the hitherto-unexplored polar plasma environment, where magnetospheric currents crash into the turbulent atmosphere to generate powerful aurorae.

Venus In Situ Explorer

On descent, the Venus In Situ Explorer (VISE) mission will make compositional and isotopic measurements of the atmosphere and—quickly—of the surface. It will loft a core sample from Venus’s hellish surface to cooler altitudes, where further geochemical and mineralogical data will be obtained. VISE will provide key measurements of the lower atmosphere and of surface-atmosphere interactions on Earth’s would-be twin. The project will elucidate the history and stability of Venus’s atmospheric greenhouse and its bizarre geological record. It will also advance the technologies required for the sample return from Venus expected in the following decade.

Comet Surface Sample Return

The Comet Surface Sample Return (CSSR) mission will collect materials from the near surface of an active comet and return them to Earth for analysis. These samples will furnish direct evidence on how cometary activity is driven. Information will be provided on the manner in which cometary materials are bound together and on how small bodies accrete at scales from microns to centimeters. By comparing materials on the nucleus against the coma’s constituents, CSSR will indicate the selection effects at work. It will also inventory organic materials in comets. Finally, CSSR will yield the first clues on crystalline structure, isotopic ratios, and the physical relationships between volatiles, ice, refractory materials, and the comet’s porosity. These observations will give important information about the building blocks of the planets.

Small Missions

Recommendations for small missions include a series of Discovery flights at the rate of at least one every 18 months and an extension to the Cassini-Huygens mission (Cassini Extended), presuming that the nominal mission is successful. Discovery missions are, by intent, not subject to long-term planning. Rather, they exist to create frequent opportunities to fly small missions addressing fundamental scientific questions and to pursue new research problems in creative and innovative ways.

Recommended Mars Flight Missions

For Mars exploration, the SSE Survey endorses the current science-driven strategy of seeking (i.e., remote sensing), in situ measurements (science from landers), and sampling to understand Mars as a planet, understand its astrobiological significance, and afford unique perspectives about the origin of life on Earth. The evolution of life and planetary environments are intimately tied together. To understand the potential habitability of Mars, whether it has or has not supported life, we must understand tectonic, magmatic, and hydrologic evolution as well as geochemical cycles of biological relevance. The return of materials from known locations on Mars is essential in order to address science goals, including those of astrobiology, and to provide the opportunity for novel measurements, such as age-dating and ultimate ground-truth.

Mars Smart Lander

The Mars Smart Lander (MSL) mission will conduct in situ investigations of a water-modified site that has been identified from orbit. It will provide ground truth for orbital interpretations and test hypotheses for the formation of geological features. The types of in situ measurements possible include atmospheric sampling, mineralogy and chemical composition, and tests for the presence of organics. The mission should either drill to get below the hostile surface environment or have substantial ranging capability. While carrying out its science mission, MSL should test and validate technology required for later sample return.

Mars Long-Lived Lander Network

The Mars Long-Lived Lander Network (MLN) is a grid of science stations making coordinated measurements around Mars’s globe for at least 1 martian year. The highest-priority objectives for network science on Mars are the determination of the planet’s internal structure, including its core; the elucidation of surface and near-surface composition as well as thermal and mechanical properties; and extensive synoptic measurements of the atmosphere and weather. In addition, heat flow, atmospheric gas isotopic observations (to constrain the size of currently active volatile reservoirs), subsurface oxidizing properties, and surface-atmosphere volatile exchange processes will be valuable. This mission will complement the much-more-limited and localized French NetLander that will have four probes spaced across Mars’s equatorial regions.

Mars Sample Return

Mars Sample Return (MSR) is required in order to perform definitive measurements to test for the presence of life, or for extinct life, as well as to address Mars’s geochemical and thermal evolution. Further, Mars’s atmosphere and now frozen hydrosphere will require highly sophisticated measurements and analytical equipment. To accomplish key science goals, samples must be returned from Mars and scrutinized in terrestrial laboratories. For these reasons, the SSE Survey recommends that NASA begin its planning for Mars Sample Return missions so that their implementation can occur early in the decade 2013-2023. Current studies of simplified Mars sample-return missions indicate that such missions are now within technological reach. Early on, NASA should engage prospective international partners in the planning and implementation of MSR.

Small Missions

Mars Scout missions are required in order to address science areas that are not included in the core program and to respond to new discoveries derived from current and future missions. A series of such small (<$325 million) missions should be initiated within the Mars program for flights at alternating Mars launch opportunities. This program should be modeled on the Discovery program.

Mars Upper Atmosphere Orbiter (MAO) is a small mission dedicated to studies of Mars’s upper atmosphere and plasma environment. This mission would provide quantitative information on the various atmospheric escape fluxes, thus quantifying current escape rates and providing a basis for backward extrapolation in our attempt to understand the evolution of Mars’s atmosphere.

Technology Directions

A significant investment in advanced technology development is also needed for the recommended new and future flight missions to better succeed. Table ES.3 identifies a number of important areas in which technology development is appropriate. The SSE Survey recommends that NASA commit to significant new investments in advanced technology so that future high-priority flight missions can succeed.


In an era of competitively selected missions for space exploration, it will continue to be necessary to improve the technical expertise and infrastructure of organizations providing the vital services that enable the planning and operation of all solar system exploration missions.

For missions to be the most productive scientifically, a level of funding must be ensured that is sufficient not only for the successful operation of the flight but also for the contemporaneous analysis of the data and the publication of scientific results. Moreover, the SSE Survey’s mission priorities rest on a foundation that must be secured and buttressed. This foundation includes fundamental research, technology development, follow-on data analysis, ground-based facilities, sample-analysis programs, and education and public outreach activities.

The entire pipeline that brings data from distant spacecraft to the broad research community must be systematically improved. Insufficient downlink communications capacity through the Deep Space Network (DSN) currently restricts the return of data from all missions, as occasionally does the DSN’s limited geographical coverage. The DSN needs to be continually upgraded as new technologies become available and system demands increase.

Once data are on the ground, they must be swiftly archived in a widely accepted and usable format. The Planetary Data System (PDS) should be included as a scientific partner at the very early stages of missions; its must be sized to accomplish its future tasks. In order to utilize the returned information effectively, analysis programs ought to be in place to fund investigators immediately upon delivery of ready-to-use data to the PDS. Data-analysis programs should be merged across lines (e.g., Discovery, New Frontiers) rather than being tied to individual missions. A healthy research and analysis (R&A) program is the most basic requirement for a successful program of flight missions. The SSE Survey recommends an increase over the decade in the research and analysis programs at a rate above inflation that parallels the increase in the number of missions, amount of data, and diversity of objects studied. Previous National Research Council (NRC) studies have shown that after a serious decline in the early to mid-1990s,i the overall funding for R&A programs in NASA’s Office of Space Science climbed in recent years to approximately 20 percent of the overall flight-mission budget.ii Figures supplied by NASA’s Solar System Exploration program show that the corresponding value for planetary activities is currently closer to 25 percent and is projected to stay at about this level for the next several years. The SSE Survey believes that this is an appropriate allocation of resources.

NASA’s Astrobiology program has appropriately become deeply interwoven into the solar system exploration research and analysis program. The SSE Survey encourages NASA to continue the integration of astrobiology science objectives with those of other space science disciplines. Astrobiological expertise should be called upon when identifying optimal mission strategies and design requirements for flight-qualified instruments that address key questions in astrobiology and planetary science.

Ground-based telescopes have been responsible for several major discoveries in solar system exploration during the past decade. Moreover, many flight missions are greatly enhanced as a result of extensive ground-based characterization of their targets. The SSE Survey recommends that NASA partner equally with the National Science Foundation to build and operate a survey facility such as the Large-aperture Synoptic Survey Telescope (LSST), described in Astronomy and Astrophysics in the New Millennium,iii to ensure that LSST’s prime solar system objectives are accomplished. Other powerful new facilities highlighted in that report—for example, the Next Generation Space Telescope—should be designed, where appropriate, to be capable of observing moving solar system targets. In addition, NASA should continue to support ground-based observatories for planetary science, including the planetary radar capabilities at the Arecibo Observatory in Puerto Rico and in Goldstone, California, the Infrared Telescope Facility on Mauna Kea in Hawaii, and shares of cutting-edge telescopes such as the Keck telescopes on Mauna Kea, as long as they continue to be critical to missions and/or scientifically productive.

In anticipation of the return of extraterrestrial samples from several ongoing and future missions, an analogue to the data pipeline must be developed for cosmic materials. The SSE Survey recommends that well before cosmic materials are returned from planetary missions, NASA should establish a sample-analysis program to support instrument development, laboratory facilities, and the training of researchers. In addition, planetary protection requirements for missions to worlds of biological interest will require investments, as will life-detection techniques, sample quarantine facilities, and sterilization technologies. NASA's current administrative activities to develop planetary protection protocols for currently planned missions are appropriate.

Education and Public Outreach activities connect solar system exploration with its ultimate customers—the tax-paying public—and as such are an extremely important component of the program. Solar system exploration captures the imagination of young and old alike. By correctly illustrating the scientific method at work and demonstrating scientific principles, the planetary science community’s efforts in communicating with students and lay people can be influential in helping to improve science literacy and education. In most implementations today, planetary scientists and education specialists work hand-in-hand to derive innovative and effective activities for communicating about solar system exploration with students, teachers, and the public. Although some problems remain, this program is well managed and is on a solid foundation.


For nearly 40 years, the U.S. Solar System Exploration program has led to an explosion of knowledge and awe with respect to our celestial neighborhood as ground-based telescopes and spacecraft have become much more capable while reaching out farther from Earth. We are now poised to address issues about our origins that have puzzled our forebears since civilization’s beginning. Answers to profound questions about our origins and our future may be within our grasp. This survey describes an aggressive and yet rational strategy to deepen our analysis of such questions and finally resolve many long-standing mysteries during the next decade.


i. Space Studies Board, National Research Council, Supporting Research and Data Analysis in NASA’s Science Programs: Engines of Innovation and Synthesis, National Academy Press, Washington, D.C., 1998, pp. 48-50.

i. Space Studies Board, National Research Council, Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data, National Academy Press, Washington, D.C., 2002, pp. 68-69.

iii. Board on Physics and Astronomy and Space Studies Board, National Research Council, Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C., 2001.


TABLE ES.1 Crosscutting Themes, Key Scientific Questions, Missions, and Facilities

Recommended New Missions and Facilities

The First Billion Years of Solar System History

1. What processes marked the initial stages of planet and satellite formation?
Comet Surface Sample Return

Kuiper Belt-Pluto Explorer

South Pole-Aitken Basin Sample Return

2. How long did it take the gas giant Jupiter to form, and how was the formation of the ice giants (Uranus and Neptune) different from that of Jupiter and its gas giant sibling, Saturn?
Jupiter Polar Orbiter with Probes

3. How did the impactor flux decay during the solar system’s youth, and in what way(s) did this decline influence the timing of life’s emergence on Earth?
Kuiper Belt-Pluto Explorer

South Pole-Aitken Basin Sample Return

4. What is the history of volatile compounds, especially water, across the solar system?
Comet Surface Sample Return

Jupiter Polar Orbiter with Probes

Kuiper Belt-Pluto Explorer

5. What is the nature of organic material in the solar system and how has this matter evolved?
Comet Surface Sample Return

Cassini Extended

6. What global mechanisms affect the evolution of volatiles on planetary bodies?
Venus In Situ Explorer

Mars Upper Atmosphere Orbiter

The Origin and Evolution of Habitable Worlds
7. What planetary processes are responsible for generating and sustaining habitable worlds, and where are the habitable zones in the solar system?
Europa Geophysical Explorer

Mars Smart Lander

Mars Sample Return

8. Does (or did) life exist beyond Earth?
Mars Sample Return

9. Why have the terrestrial planets differed so dramatically in their evolutions?
Venus In Situ Explorer

Mars Smart Lander

Mars Long-Lived Lander Network

Mars Sample Return

10. What hazards do solar system objects present to Earth's biosphere?
Large-aperture Synoptic Survey Telescope

11. How do the processes that shape the contemporary character of planetary bodies operate and interact?
Kuiper Belt-Pluto Explorer

South Pole-Aitken Basin Sample Return

Cassini Extended

Jupiter Polar Orbiter with Probes

Venus In Situ Explorer

Comet Surface Sample Return

Europa Geophysical Explorer

Mars Smart Lander

Mars Upper Atmosphere Orbiter

Mars Long-Lived Lander Network

Mars Sample Return

12. What does the solar system tell us about the development and evolution of extrasolar planetary systems, and vice versa?
Jupiter Polar Orbiter with Probes

Cassini Extended

Kuiper Belt-Pluto Explorer

Large-aperture Synoptic Survey Telescope

NOTE: Since missions in the Discovery and Mars Scout lines might address many of these scientific topics, they are not shown, in order to maintain clarity.

TABLE ES.2 Prioritized List of New Flight Missions for the Decade 2003-2013

Priority in Cost Class
Mission Concept Name


Small (< $325 million)

Discovery missions at one launch every 18 months
Small, innovative, principal-investigator-led exploration missions

Cassini Extended
Orbiter mission at Saturn

Medium (< $650 million)

Kuiper Belt-Pluto Explorer
A flyby mission of several Kuiper Belt objects, including Pluto/Charon, to discover their physical nature and understand their endowment of volatiles

South Pole-Aitken Basin Sample Return
A mission to return samples from the solar system’s deepest crater, which pierces the lunar mantle

Jupiter Polar Orbiter with Probes
A close-orbiting polar spacecraft equipped with various instruments and a relay for three probes that make measurements below the 100+ bar level

Venus In Situ Explorer
A core sample of Venus to be lifted into the atmosphere for compositional analysis; simultaneous atmospheric measurements

Comet Surface Sample Return
Several pieces of a comet’s surface to be returned to Earth for organic analysis

Large (>$650 million)

Europa Geophysical Explorer
An orbiter of Jupiter’s ice-encrusted satellite to seek the nature and depth of its ocean


Small (< $325 million)

Mars Scout line
A competitively selected line of Mars missions similar in concept to Discovery

Mars Upper Atmosphere Orbiter
A spacecraft dedicated to studies of Mars’s upper atmosphere and plasma environment

Medium (< $650 million)

Mars Smart Lander
A lander to carry out sophisticated surface observations and to validate sample-return technologies

Mars Long-Lived Lander Network
A globally distributed suite of landers equipped to make comprehensive measurements of the planet’s interior, surface, and atmosphere

Large (>$650 million)

Mars Sample Return
A program to return several samples of the red planet to search for life, develop chronology, and define ground-truth.

TABLE ES.3 Recommended Technology Developments

Recommended Development

Advanced radioisotope power sources, in-space fission-reactor power source

Nuclear-electric propulsion, advanced ion engines, aerocapture

Ka band, optical communication, large antenna arrays

Autonomy, adaptability, lower mass, lower power

Advanced packaging and miniaturization, standard operating system

Miniaturization, environmental tolerance (temperature, pressure, and radiation)

Entry to landing
Autonomous entry, precision landing, and hazard avoidance

In situ operations
Sample gathering, handling, and analysis; drilling; instrumentation

Autonomy; surface, aerial, and subsurface mobility; access to hard-to-reach places

Means of avoiding forward-contamination

Earth return
Ascent vehicles, in-space rendezvous, and Earth-return systems