Assessment of Mars Science and Mission Priorities (2003)

Within the Office of Space Science of the National Aeronautics and Space Administration (NASA) special importance is attached to exploration of the planet Mars, because it is the most like Earth of the planets in the solar system and the place where the first detection of extraterrestrial life seems most likely to be made. The failures in 1999 of two NASA missions—Mars Climate Orbiter and Mars Polar Lander—caused the space agency’s program of Mars exploration to be systematically rethought, both technologically and scientifically. A new Mars Exploration Program plan (summarized in Appendix A) was announced in October 2000. The Committee on Planetary and Lunar Exploration (COMPLEX), a standing committee of the Space Studies Board of the National Research Council, was asked to examine the scientific content of this new program. The charge to COMPLEX was as follows:

• Review the state of knowledge of the planet Mars, with special emphasis on findings of the most recent Mars missions and related research activities;

• Review the most important Mars research opportunities in the immediate future;

• Review scientific priorities for the exploration of Mars identified by COMPLEX (and other scientific advisory groups) and their motivation, and consider the degree to which recent discoveries suggest a reordering of priorities; and

• Assess the congruence between NASA’s evolving Mars Exploration Program plan and these recommended priorities, and suggest any adjustments that might be warranted.

COMPLEX comprehensively reviewed Mars science in nine disciplinary areas, working its way from the interior of the planet (Chapter 2) outward to the upper atmosphere (Chapter 10). The committee heard presentations by experts in all these areas and wrote chapters with structures modeled after the charge: Each chapter begins with a review of the present state of knowledge and then discusses near-term opportunities, presents recommended scientific priorities, and offers an assessment of priorities in the Mars Exploration Program.

COMPLEX drew on the publications of 11 earlier committees (including reports from both COMPLEX in years past and NASA) to compile its recommended scientific priorities; these sets of previously published recommendations appear in Appendix B. A document prepared in 2001 by James B. Garvin and Orlando Figueroa of the

NASA Office of Space Science, titled “The Mars Exploration Program: A High-level Description” (reprinted in Appendix A of this report), provided the basis for comparisons with the recommendations, which appear in the section “Assessment of Priorities in the Mars Exploration Program” in each of Chapters 2 through 10. Chapter 12 is a synthesis of the assessments of priorities that appear in Chapters 2 through 10.

COMPLEX judged NASA’s responsiveness to the past recommendations of advisory panels to be, on the whole, good, although there is weakness in some areas. COMPLEX acknowledges that budgetary constraints prevent all worthy research goals from being pursued simultaneously, and it endorses the space agency’s concentration of effort in areas related to the fundamental question, Did life ever arise on Mars? It is important that efforts to answer this question be broadly based and equally prepared for a negative or positive answer. The implications of either answer to the question will be fully understood only when a broad and deep understanding of Mars has been acquired.

The new Mars Exploration Program recognizes the importance of gaining information about the surface, atmosphere, hydrosphere, and interior of the planet to arrive at an understanding of the Mars dynamic system and a global context for assessment of the biological potential of Mars (see Chapter 12). However, COMPLEX notes that NASA has no plans for missions that address high-priority questions about the interior of Mars. Similarly, there is an absence of NASA missions that specifically address Mars’s atmosphere, climate, polar science, ionosphere, and solar wind interactions. Direct measurements of the distribution and behavior of near-surface water are needed. Some but not all of these goals will be addressed by upcoming foreign Mars missions such as Japan’s Nozomi, the European Space Agency’s Mars Express, the United Kingdom’s Beagle 2, and France’s NetLander. COMPLEX urges NASA to continue its support for U.S. participation in Mars missions conducted by NASA’s international partners. A full picture of the science of Mars is needed to support the quest for martian life.

Water is a topic of particular interest on Mars, not only for its own sake but because it is a prerequisite for life. This is so widely recognized as to have engendered the slogan in advisory and planning circles, “Follow the water.” In light of this, there is surprisingly little emphasis on spacecraft experiments designed to detect and study crustal water and ice. COMPLEX believes that this subject needs more attention. In Chapter 12 COMPLEX offers for consideration 10 spacecraft experiments that it considers would advance Mars science, but the committee attempts to be realistic about the factors that militate against them.

COMPLEX attaches special importance to the prospect of sample-return missions to Mars (see Chapter 11). The return of Mars samples has been consistently advocated by advisory panels for more than 20 years as the most effective way to greatly increase our understanding of the history of Mars and its surface environment. No other single strategy can answer so many of the questions about martian chemistry, geology, climatology, and the presence of or potential for life, past or present. Irrespective of the number of orbiters or rovers sent to Mars, we will not come to grips with these fundamental issues until documented samples are available for study in terrestrial laboratories.

The committee believes that enough information is at hand already, much of it from the Mars Global Surveyor mission, to choose the first sites to be sampled intelligently, and that sample return need not wait on additional reconnaissance missions (see Chapters 11 and 12). Even if the first returned samples are not optimal in terms of siting, they will provide a greatly enhanced view of the geologic processes on Mars. Even a “grab sample” of soil from a randomly chosen site on the planet would reveal the character of martian surface material: its chemistry, oxidation state, content of organic materials, mineralogy, and the history of weathering reactions that has affected it. Detailed knowledge of the surface material will permit a more intelligent choice of measurements to be made by future remote-sensing missions. Exercise of selectivity in landing sites will open additional doors: Samples from a formerly fluvial environment, for example, may be found to include rocks of diverse composition and age, including sedimentary rocks that contain a record of aqueous activity on the martian surface, conceivably even fossil evidence of life.

Since sample-return missions are expensive and will tend to preempt the resources of the Mars Exploration Program, a key question is how many of them are needed. COMPLEX concluded that it cannot be realistically

anticipated that the first sample return from Mars will unlock all of the planet’s secrets. Orbital observations have shown that Mars’s geologic and climatic history is best exposed in widely separated, isolated locations, and a complete picture of martian history is unlikely to be obtained from samples collected at a single location. Instead, the first sample return should be seen as a trailblazer for future sample-return missions, and it should be used to develop the key technologies, procedures, and infrastructure necessary to embark on a future program in which samples are returned from many locations on the planet. COMPLEX estimates that roughly 10 sample-return missions, necessarily executed over a protracted period of time—perhaps three or four decades to as much as a century—may be required to learn the most important things researchers want to know about Mars. A protracted schedule of exploration will allow time for the information gained by each mission to be digested and fed into the planning of the next mission, and it will permit substantial redesign of the spacecraft and sampling system between missions.

Considerations of planetary protection dictate that stringent measures be taken during a sample-return mission to prevent biological contamination of either Earth or Mars. One essential measure is the construction of a quarantine facility to receive and contain samples when they arrive on Earth. COMPLEX reiterates the conclusion of its recent report on the design and operation of a Mars Quarantine Facility—that a long lead time is required to prepare such a facility.^a On the basis of prior experience with facilities of this type, COMPLEX estimated that 7 years will be required to design, construct, and staff the facility. To this period must be added the time needed to clear an environmental impact statement and to carry out several reconnaissance studies that are needed to inform the design and operation of the facility.^b The aggregate of time required may strain the schedule even of a 2011 launch. The message is plain: Preparations for sample return should not be delayed any longer than they already have been (see Chapter 12).

Chapter 7 elaborates on this recommendation, reiterating the conclusions of COMPLEX’s recent report on the quarantine of martian samples. In summary, these conclusions are as follows:

• The Mars Quarantine Facility in which Mars samples will be processed, stored, and released for scientific study, and in which a very limited range of studies will be carried out, must be designed, built, and certified.

• Research must be initiated on several outstanding questions that will affect the design of the Mars Quaran-tine Facility (e.g., combining biological isolation with clean-room conditions; establishing the efficacy and detrimental effects of sterilization techniques).

• The study of life in extreme environments on Earth, which can aid in the design of life-detection tests, should be supported, as is already being done. In general, research areas that improve the sensitivity of life-detection techniques must be supported, and a life-detection protocol to be implemented and tested in the Mars Quarantine Facility must be developed.

• Techniques must be developed for the collection, packaging, and return of samples.

• The research programs of Mars orbiter and lander missions must be designed to support the collection of those samples with the greatest potential for life detection (this process is underway).

COMPLEX also considered several other topics important to Mars exploration (see Chapter 12), including those addressed below.

An extremely important consideration in establishing the capabilities of landed packages, static or roving, on Mars is the power supply on which they rely—the options being solar panels and radioisotope power systems. The limitations placed on landed spacecraft by solar power supplies are reviewed. From a science viewpoint, the advantages of nuclear power—namely, long-lived missions, night-time operation, and access to any point on Mars—are clear. COMPLEX urges the use of radioisotope power systems, if at all feasible, on advanced Mars lander missions.

There is concern in the scientific community that the Mars Scout Program, the youngest and smallest element of the Mars Exploration Program, may also be the most vulnerable. The fear is that the Scout Program may not achieve its potential because it will be sacrificed in times of budget stringency. COMPLEX considers that this would be unfortunate.

COMPLEX also noted that the Mars Exploration Program, with its missions at 2-year intervals, presents a new problem in fully exploiting the amount and variety of data that will be collected. The volume and quality of data returned by Mars Global Surveyor alone have been extraordinary, and the analysis of these data is only beginning. With the rapid pace of Mars missions planned for the next decade, the flood of data can be expected to increase. This problem should be recognized, and NASA’s data analysis and science programs should be structured to accommodate and support the broad range of Mars science that is to come.

The Mars Exploration Program consists of a queue of flight missions, so the present assessment of the program also discusses flight missions and rarely touches on Earth-based research. However, the latter is an essential component of the total program of Mars research, and in Chapter 1 of this report, COMPLEX acknowledges several areas of Earth-based Mars research, urging continued support of these and other areas of Earth-based research, because they are essential to a balanced program of Mars research.