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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 1990 Update to Strategy for Exploration of the Inner Planets 6 Mars PROGRESS Although only one spacecraft, the short-lived Soviet PHOBOS mission, has encountered Mars since 1978, the last decade has produced a significant evolution of thought in many areas. Further, both the United States and the Soviet Union have begun to build new spacecraft. Viking observations continued through 1982, and major advances in data analysis and modeling have added to our previous understanding of the planet. The discovery that SNC-class meteorites are likely pieces of Mars that have been transported to Earth possibly provides a direct sample of some part of the Martian surface. Viking orbiter imaging data provided as much as an order-of-magnitude increase in visible detail and facilitated a major increase in our understanding of the global stratigraphy and the geologic history of the planet. A broad picture of the evolution of the planet's surface since about 4 billion years ago has emerged, but there are stall major uncertainties concerning the events in the earliest history of Mars;, and about the nature and timing of specific geologic processes since then. Some of these include the mechanisms responsible for the global crustal dichotomy, the tectonic history within and outside of the Tharsis region, the chronicling of erosional processes, and the role and history of water in forming channel systems on the older and on younger terrains. A global understanding of aspects of the climate system has also developed. Detailed analyses and modeling have been done of the seasonal variations of water vapor in the atmosphere and of the seasonal exchange and transport processes, the polar-cap energy balance, and an entire Mars year of atmospheric dust opacity measurements. Combined with a dramatic improvement in our understanding of and ability to model the atmospheric dynamics, these have led to major advances in our understanding of the atmospheric circulation and radiative (1 of 5) [6/18/2004 10:07:00 AM]

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Space Studies Board processes. One important result was to establish that global dust storms occur during some years but not during others, with different dynamical regimes being represented. In conjunction with chemical analysis of the surface materials, these data also constrain the history of the near-surface deposits. The distribution and properties of materials within the near-surface layer have also been mapped using thermal infrared and Earth-based radar remote sensing data and imaging observations of variable features. In combination with information on the abundance and transport of dust within the atmosphere, these data constrain the present Martian aeolian environment. The search for life dominated the Viking lander science interests. The conclusions, after a fair amount of discussion, are that the data are most consistent with the absence of life. The complete absence of organic material in the soil is the strongest argument against the extant existence of biological material in the form with which we are familiar. Nevertheless, consistent with the SSB report Planetary Biology and Chemical Evolution: Progress and Future Directions (National Academy Press, Washington, D.C., 1990), the committee endorses the continued search for evidence of past life and biochemical evolution on Mars, as well as the continuing study of the history of water on Mars. SCIENTIFIC OBJECTIVES The 1978 strategy described five broad categories of prioritized primary scientific objectives for Mars. These were as follows: 1. The intensive study of local areas. Of special importance were the mineralogical, chemical, and petrological properties of the surface; the nature and chronology of major surface-forming processes; the nature of surface, subsurface, and atmospheric volatiles and their interaction with the surface; and the interactions of radiation with the surface. 2. The study of the structure and circulation of the Martian atmosphere. Global atmospheric and boundary layer processes were specifically called out, requiring orbital remote sensing and multiple ground stations measuring several meteorological parameters. 3. The study of the structure and dynamics of Mars's interior. Specific areas of study included topography and gravity field investigations, seismological study of the interior, and surface beacon tracking to directly determine the planet's precessional constant and thus its moment of inertia. 4. The study of the nature of the Martian magnetic field and the character of the upper atmosphere, and their interactions with the solar wind. These processes and phenomena remain essentially unexplored. 5. The study of the .global chemical and physical properties of the Martian surface. (2 of 5) [6/18/2004 10:07:00 AM]

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Space Studies Board Measurements of these properties would provide constraints on the global crustal composition and its spatial variations, and would place the results of local intensive studies into a global context. UPDATED RECOMMENDATIONS Although the primary objective for Mars laid out in the 1978 report involved the intensive study of local areas, the intervening decade has seen a major research emphasis in areas addressed by some of the other objectives. This shift of emphasis was primarily fueled by analysis and modeling of Viking data, as well as additional Earth-based telescopic data. These studies showed the importance of global and regional processes on Mars, especially in comparison with similar processes on the Earth and Venus. Examples include the triggering of global dust storms, the `history of the; Martian climate, surface-atmosphere interactions affecting the history of volatiles, polar processes, and the role of the Tharsis uplift. From this perspective, while intensive local studies remain the single highest- priority objective, COMPLEX considers that the importance of the other four objectives has increased relative to their standing in the 1978 report and should norv be treated as having equal priority. Furthermore, the discussion of the first objective in the 1978 report and the quantitative specifications given there for the types and precision of measurements required to satisfy it point unambiguously to in situ investigations on the surface of the planet and to sample return. The objective can certainly be implemented in full only in this way. The committee notes, however, that a decade later the unexpected sensitivity and spatial and; spectral resolution of several types of instruments are such that certain orbital measurements are capable of providing information on a local surface scale that bears on some aspects of this objective. As described in the 1978 report, the detailed analysis of surface materials involved samples to be collected from a region within easy reach of a landed vehicle. The current. scientific consensus is that such samples are no longer considered. adequate to address this objective. Rather, samples need to be obtained. from a variety of locations spread out over perhaps hundreds to thousands of kilometers, and they need to be identified with sufficient information to provide the geologic context for each sample. A collection of materials chosen from those present only in the immediate vicinity of a single landed vehicle would not be adequate. The lowest-priority objective in the 1978 report involved the global chemical and physical characterization of the Martian surface. Since this task was nevertheless included as a primary scientific objective, the committee at that time explicitly recognized the importance of characterizing whole-planet, major regional-scale and intermediate-scale features, as distinguished from information at the local (a few kilometers) scale. However, only determination of whole-planet and major-unit chemical composition at low spatial resolution from orbit is called out specifically in the 1978 statement of measurement requirements. Remote sensing instruments that are either available now or are under development permit the committee to (3 of 5) [6/18/2004 10:07:00 AM]

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Space Studies Board extend this objective to include regional and .intermediate-scale surveys of surface mineralogy and physical properties (e.g., density and grain size)—a particularly important consideration for Mars, with its chemical and physical diversity at various scales. From its present perspective, the committee perceives this objective as being on an equal footing with objectives 2, 3, and 4 above. Understanding of the spatial and temporal distribution of minor species in the Martian atmosphere would provide insight into the global atmospheric chemistry and the stability and evolution of the atmosphere. Photochemically produced species such as CO, O2, and OH and species that evolve over time, such as those including deuterium, need to be measured at altitudes up to 80 km. Direct measurements of the wind velocity profile as well as of surface winds are also required. An understanding of the global distribution of ice clouds is necessary due to its possible importance in the hydrologic cycle. Because of the importance of the polar caps in controlling the present climate, their seasonal behavior needs to be better understood. Measurements of the energy balance and seasonally variable composition are required, along with observations pertinent to .the interactions with the atmosphere, net annual loss or gain of different constituents from the caps, and year-to-year variations in their behavior. The importance of these processes in the evolution of the polar layered terrain and the implications of the structure of the layered terrain for understanding the integrated effects of these processes provide impetus for detailed study of the layered terrain as well. Global Viking imaging at 100-m resolution and some imaging at 10-m resolution have not adequately and uniquely determined all details of the geologic history of the surface. Global compositional mapping at kilometer-scale resolution, combined with imaging of selected areas at higher resolution, would give us significant new information in this area. Determination of the global and local heat flux from the interior, along with the presence or absence of an intrinsic magnetic field, would provide important constraints on the bulk composition and thermal history of the interior. As noted at the outset, observations of the surface and atmosphere of Mars were made in 1989 by the Soviet PHOBOS orbiter. Measurements made by several instruments were relevant to a better understanding of atmospheric and surface properties and composition, primarily in the equatorial regions, and have provided data on the Martian magnetosphere and its interaction with the solar wind. Although these data have not been completely analyzed, it is unlikely, due to the short mission lifetime and limited geographic extent of observations, that any of the major goals outlined in the 1978 report were completely addressed. The U.S. Mars Observer mission is a near-polar orbiting spacecraft scheduled for launch in 1992, with global mapping to begin in 1993. Its goal is to map the surface and atmosphere for an entire Martian year. (4 of 5) [6/18/2004 10:07:00 AM]

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Space Studies Board If Mars Observer is successful, the original COMPLEX objectives of establishing the nature of the magnetic field and characterizing the global distribution of chemical and physical characteristics of the surface will be partly accomplished. In addition, contributions will be made to the objectives of exploring atmospheric structure and circulation, establishing the distribution of volatiles, and constraining the planet's interior structure by means of topography and gravity data: Mars Observer will also provide a base of data to guide the selection of sampling sites for a Mars sample return mission and to identify resources to be used in potential future human exploration of the planet. The principal components of the 1978 report's objectives that will remain largely unaddressed after a successful Mars Observer mission are the prime objective of in situ (or remotely sampled) elemental, mineralogical, and petrological studies of selected areas; seismological and precessional studies of the interior structure of the planet; and the dynamical and chemical properties of the upper atmosphere and its interactions with the solar wind. Also open will be the question of past life on Mars. If life developed in the more clement ages on Mars, it may have left chemical and fossil evidence. COMPLEX therefore recommends that the geochemical, isotopic, and paleontological study of Martian surface material for evidence of previous living material be a prime objective of future in situ and sample return missions. Last update 9/26/00 at 2:29 pm Site managed by Anne Simmons, Space Studies Board Site managed by the SSB Web Group. To comment on this Web page or report an error, please send feedback to the Space Studies Board. Subscribe to e-newsletters | Feedback | Back to Top Copyright © 2004. National Academy of Sciences. All rights reserved. 500 Fifth St. N.W., Washington, D.C. 20001. Terms of Use and Privacy Statement (5 of 5) [6/18/2004 10:07:00 AM]