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Space Studies Board Search: Jump to Top NewsJump to Science in the Subscribe to our FREE e- Headlines newsletter! NATIONAL ACADEMY OF SCIENCES NATIONAL ACADEMY OF ENGINEERING INSTITUTE OF MEDICINE NATIONAL RESEARCH COUNCIL June 18, 2004 Current Operating Status International Cooperation for Mars Exploration and Sample Return 3 Intensive Investigations of Mars GENERAL CHARACTERIZATION OF THE PLANET The martian surface has clearly evolved under the influence of a variety of processes of internal, surficial, and external origin. The major processes that shaped the surface of Mars include eruption and emplacement of volcanic deposits, water erosion and sedimentation, impacts, and faulting and other tectonic processes, as well as glacial phenomena. Valles Marineris, a canyon system more than 4000 kilometers long, seems to have been the result of rifting and other tectonic processes as well as major erosion. Extensive layered deposits are visible in the sides of the canyons and in the associated mesas. Some of these deposits may have arisen as sediments in vast lakes that once filled parts of the canyon system. However, other speculations are that some layered deposits resulted from lava flows, explosive volcanic deposits, or wind-laid sediments. Regardless of the origin, these layered deposits and the canyon walls may reveal critical clues about a large part of martian history, in much the same way that the deposits and walls in Arizona's Grand Canyon reveal much about Earth's history. Some regions of Mars are dissected by large and small channels apparently cut through young rock, indicating that liquid water existed on the surface of Mars relatively late in the planet's history. Other, more degraded, channels dissect ancient terrain and appear to have formed earlier in the history of the planet. Altogether, the present indirect clues suggest the likelihood of profound climatic change on Mars, including the possibility that flowing water occurred at least several times throughout the history of the planet. Mars has distinct seasons, with carbon dioxide cycling between the polar caps driving a major component: of the atmospheric circulation. Layered sedimentary deposits near the martian poles provide additional evidence of long-term climatic changes whose origins are poorly understood and that pose some of the most http://www7.nationalacademies.org/ssb/marscoopch3.html (1 of 4) [6/18/2004 10:03:54 AM]
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Space Studies Board fundamental scientific questions motivating intensive Mars investigation. On Earth, such climatic change has given rise to the occasional ice age, a phenomenon also still poorly understood. The Viking mission indicated the absence of even relatively small amounts of organic molecules on Mars. Viking also confirmed the existence of intensely oxidizing conditions at the martian surface. These factors strongly suggest that living organisms are not now present. Whether Mars was less hostile to the development of life during earlier times, when it may have had a denser atmosphere, higher surface temperatures, and liquid water, is still an open question. So far as is known, Earth is the only planet with surface conditions, an atmosphere, and a hydrosphere that have allowed the formation of life as well as its sustenance and evolution over a long period of time. Terrestrial life forms have substantially altered the chemistry of the atmosphere, oceans, and major sedimentary rocks on Earth's surface. Fundamental questions to be addressed through investigations of Mars also include questions about the role' that life plays in the evolution of a planetary surface and environment; these questions are most effectively addressed through detailed investigation of another planet on which life seems to have played a much smaller role than it has on Earth, or no role at all. Other basic questions about Mars include the state and evolution of the planet's interior, the physical processes that have shaped the surface, the fate of the apparently missing water, and the nature of current and past hydrological cycles that link the polar caps, ground water, and atmosphere. THE SCIENTIFIC AND TECHNICAL CHARACTER OF MARS EXPLORATION The scientific objectives of intensive Mars investigation are to understand the planet's gross planetological characteristics, the principal processes that govern its present state, the history of variation in the martian environment, and phenomena that have been responsible for such environmental change. It is also a principal objective to ascertain whether any stages of chemical and biological evolution might have occurred on Mars and to determine whether evidence can be found for the existence of life at any time during the history of the planet. Strategies and approaches for achieving these scientific goals have been analyzed in previous Space Studies Board and NASA reports. 1,5,6,10 In this report the committee briefly summarizes those conclusions in order to define the context of scientific objectives in which its recommendations about cooperation are made. Investigation of the structure and dynamics of the martian interior will require the use of a globally distributed network of sensitive seismometers—at least three—on the surface of the planet, with a substantial period of simultaneous operation extending over the order of 1 year or more. Investigation of the atmospheric circulation and climate will require at least a similar number of widely spaced monitoring stations distributed over the martian globe in latitude and longitude and operating for an overlapping interval lasting at least 1 martian year. http://www7.nationalacademies.org/ssb/marscoopch3.html (2 of 4) [6/18/2004 10:03:54 AM]
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Space Studies Board To obtain the variety of samples needed to answer the principal scientific questions, it will be necessary to obtain planetary material of a variety of ages, including material from the most ancient sites on the heavily cratered terrains, material more recently brought to the planet's surface on the intermediate-aged, resurfaced plains areas, and materials from the youngest identifiable volcanic deposits. Material spanning this range of planetary age will be necessary for tracing the planet's interior and crust. Material capturing stratigraphic records will be recoverable from crater ejecta as well as from material on channel walls. Sedimentary deposit material—including such material from beneath the surface—will be important for exploring questions pertaining to the history and nature of flowing water on Mars, and to possible biochemical and biological aspects of the planet's history. The margins of the polar ice caps, seasonal ice- related deposits, and the ice sheets themselves hold important information about the planet's volatile inventory and about climatic variation on Mars; the polar margins are also essential targets of study for questions about the past and present biological potential of the planet. Identifiable regions of contemporaneous volcanism would be important targets of investigation for studying geochemical and geophysical questions, as well as questions pertaining to the planet's biological potential. Altogether, Mars exhibits a variety of geological terrains and environments that are widely separated and distributed over the planet. The scientific objectives dictate that a variety of sites be investigated for several reasons: investigation of the global questions requires an absolute minimum of three widely separated sites; and the varieties of materials required for scientific analysis are distributed widely over the planet's surface; and the varieties of environments and manifestations of evolutionary history are distributed in many different locations on the planet. The.exact number of missions needed in the next phase of Mars intensive investigation will depend on technical details not yet resolved, including such questions as rover range and maneuverability, accuracy of lander targeting, and feasible modes of deploying scientific instruments. To obtain answers to the major scientific questions and to build an understanding, of Mars at the level needed to address comparative planetological questions will require the exploration of, and sample return from, several diverse sites—in the range of four to six. A program of this nature would also provide the base of information needed to determine the value of possible human exploration of Mars and to assess the technical questions involved in planning for possible future human exploration. Investigations of Mars will play a critical role in achieving a general understanding of the terrestrial planets and their environments. Because of the importance of a Mars program in terms of the quality and significance of the scientific objectives, the prestige and scientific importance associated with the return of the martian materials, and the substantial implications for new technologies such as robotics and artificial intelligence, this committee concurs with previous recommendations of the Space Studies Board and recommends the vigorous scientific exploration of Mars, with investigations on the martian surface and the return of marcian materials from several diverse sites, ranging from equatorial to polar, in order to http://www7.nationalacademies.org/ssb/marscoopch3.html (3 of 4) [6/18/2004 10:03:54 AM]
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