Draft 0 Mars Science Goals, Objectives, Investigations, and Priorities: 2008
C. Objective: Polar, Glacial and Periglacial Processes
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C. Objective: Polar, Glacial and Periglacial Processes:The modern Martian record of volatile reservoirs and their dynamics is uniquely manifested in the polar regions. The NRC Decadal Survey (2003) has suggested that a more complete understanding of the sources and sinks of major volatiles systems within the Solar System is a potentially paradigm-shifting priority across the next decade of planetary exploration. This overarching objective ties the modern record of climate to the migration pathways within the accessible Mars “system” of primary volatile species, including CO2 and H2O. It also serves as the context within which to document and quantify climate variability and the modern history of water in three dimensions, which links it directly to priorities within Geology and Geophysics. Given the role of volatile reservoirs in the broad theme of “habitability”, pursuit of polar processes and climatology is of significant importance in the science of Mars. The most likely location of a preserved record of recent Mars climate history is contained within the north and south polar deposits and circumpolar materials. The polar layered deposits (PLD) and residual ice caps may reflect the last few hundred thousand to few million years, while terrain softening, periglacial features, and glacial deposits at mid to equatorial latitudes reflect recent high obliquity cycles within the last few million years. Dune and mantling deposits around the northern PLD span the entire Amazonian period, ~ 3Ga to the present, and multiple sequences of deposition and erosion are recorded. Understanding the interaction between the current climate and current residual ice caps will act as a 'Rosetta stone' which we can use to interpret the layered deposits in terms of the previous climates which formed them. New observations of the permanent and seasonal polar caps have shown the complex dynamics involved in the layers active today and also the extent and consistency of layering in the polar caps themselves. Investigations specifically related to the processes and history of climate evolution include: 1. Investigation: Determine the mass, volume & energy budgets of both seasonal and residual volatile deposits, and what processes control these budgets on seasonal and longer timescales. The presence of extensive layered deposits suggests that the climate of Mars has undergone frequent and geologically recent change. A key to understanding the climatic and geologic record preserved in these deposits is to determine the environmental conditions and processes that were necessary to produce them. Specific examples of the type of information these deposits may preserve include a stratigraphic record of volatile mass balance; insolation variations; atmospheric composition; dust storm, volcanic and impact activity; cosmic dust; catastrophic floods; solar luminosity (extracted by comparisons with terrestrial ice cores); supernovae and perhaps even a record of microbial life. 2. Investigation: Understand how volatiles and dust exchange between polar and atmospheric reservoirs. Determine how this exchange has affected the past and present distribution of surface and subsurface ice as well as the PLD. 3. Investigation: Determine the chronology, including absolute ages, compositional variability, and record of climatic change that are expressed in the stratigraphy of the PLD. Other keys to understanding the climatic and geologic record preserved in these deposits is to determine (i) the relative and absolute ages of the layers, (ii) their thickness, extent and continuity, and (iii) their petrologic/geochemical characteristics (including both isotopic and chemical composition). Addressing this investigation requires high-resolution imaging, in situ and remote sensing measurements of stratigraphy and layer properties, and absolute ages determined either in situ or from returned samples. III. GOAL: DETERMINE THE EVOLUTION OF THE SURFACE AND INTERIOR OF MARS Insight into the composition, structure, and history of Mars is fundamental to understanding the solar system as a whole, as well as providing insight into the history and processes of our own planet. There are compelling scientific motivations for the study of the surface and interior of the planet in its own right. The renewed interest in the possibility of life on Mars provides additional emphasis for these investigations. The geology of Mars sheds light on virtually every aspect of the study of conditions potentially conducive to the origin and persistence of life on that planet, and the study of the interior provides important clues about a wide range of topics, such as geothermal energy, the early environment, and sources of volatiles. A critical aspect of Mars is the evidence for the presence and activity of liquid water on or near the surface over an extended period of time. This has enormous geological implications affecting, for example, erosion, weathering, heat flow, and the possibility of life (which can, in turn, have significant effects on geological processes). A. Objective: Determine the nature and evolution of the geologic processes that have created and modified the Martian crust (investigations in priority order) The Martian crust contains the record of all the processes that shaped it, from initial differentiation and volcanism, to modification by impact, wind, and water. Understanding that record will help us understand the early environment (as reflected, for example, in the alteration mineralogy), the total inventory and role of water, regions likely to have been habitable, processes involved in surface-atmosphere interactions, and the planet’s thermal history. Many of the listed investigations are interrelated and can be addressed by common data sets and/or methodologies; in many cases, the reasons for separating some subjects into different investigations have to do with issues of scale (both vertical and lateral) or geologic/geophysical process. For the purposes of Goal III, “regolith” refers to the upper few meters to hundreds of meters of the Martian surface; greater depths are treated as part of the crust. 1. Investigation: Determine the primary and alteration mineralogies of major geologic units on Mars as they relate to the formation and modification of the Martian crust and regolith. The regolith is a filter through which we view most of the Martian surface by remote sensing. In addition, it may provide a valuable record of the history of surface conditions and processes. Understanding Mars’ geologic/environmental history, including regolith formation and modification, requires quantitative measurement of mineralogy and chemistry. Identification of alteration processes requires characterization of both altered and unaltered rock. There have been considerable advances in the understanding of surface mineralogy based on remote sensing and limited in situ observations. Orbital remote sensing with high spatial and spectral resolution has demonstrated the ability to correlate mineralogy with specific geologic units. However, calibration of the orbital data with in situ direct determination of mineralogy is critical, both to ensure the interpretations based on orbital data are correct and to understand those species that either have limited spatial extent or concentration. 2. Investigation: Evaluate volcanic, fluvial/laucustrine, hydrothermal, and other sedimentary processes that have modified the Martian landscape over time. Sediments and sedimentary rocks formed in and near fluvial, laucustrine, and hydrothermal environments are the most likely materials to preserve traces of prebiotic compounds and evidence of life. In addition to connections with the earliest evolution of life on the Earth, hydrothermal systems also may play an important role in the chemical and isotopic evolution of the atmosphere, and the formation of the regolith and may record the histories of these events. Sediments and sedimentary rocks record the history of water processes. Aeolian sediments record a combination of globally averaged and locally derived fine-grained sediments and weathering products. Pyroclastic deposits record a style of volcanism that commonly involves interactions with or compositions containing relatively abundant volatiles. Understanding this wide variety of sedimentary processes requires knowledge of the ages, sequences, and mineralogies of sedimentary rocks; as well as the rates, durations, environmental conditions, and mechanics of weathering, cementation, and transport.. High spatial resolution thermal systems are required to locate active hydrothermal anomalies. 3. Investigation: Characterize the composition and dynamics of the polar layered deposits. The focus of this investigation is understanding the composition and history of the polar layered deposits (the extent to which ice and non-ice materials occur and their composition), and the rates of formation and removal of the layered materials, from seasonal to geologic time scales. This should include measurements of the physical characteristics of the polar deposits and how the different geologic units within, beneath, and surrounding the polar layered deposits are related. This should also include determining the age of the polar layered deposits and their glacial, fluvial, depositional and erosional histories, as well as in-situ analysis of multiple layers to complement and enhance constraints obtained from remote observations.
The evolution of the interior and surface, as well as the possible evolution of life, must be placed in an absolute timescale, which is presently lacking for Mars. Without an understanding of the absolute timing of events, the potential for current geologic/biologic activity remains unknown. Developing this chronology requires determining the absolute ages of crystallization or impact metamorphism of individual units with known crater densities. This will allow calibration of Martian cratering rates and interpretations of relative ages of geologic units. This investigation can be approached with both in situ and returned sample analysis, although with different precision. For example, age constraints on sedimentation, weathering, hydrothermal activity, and diagenesis could be obtained either by dating igneous materials interbedded with sedimentary rocks or in the laboratory using returned samples. 5. Investigation: Evaluate igneous processes and their evolution through time. This investigation includes the broad range of igneous processes such as the mineralogy and petrology of the rocks as well as, for example, volcanic outgassing and volatile evolution. In addition to dramatically shaping the surface of the planet, volcanic processes are the primary mechanism for release of water and atmospheric gasses. Sites of present day volcanism, if any, may be prime sites to investigate. Understanding primary lithologies also is key to interpreting alteration processes that have produced secondary mineralogies. 6. Investigation: Characterize surface-atmosphere interactions on Mars, as recorded by polar, aeolian, chemical, weathering, mass-wasting, glacial/periglacial, cratering and other processes The focus of this investigation is on processes that have operated within the recent past. Studying surficial features resulting from recent hydrologic, glacial/periglacial, cratering, mass-wasting, and atmospheric processes contributes to our understanding of which features may (or may not) indicate possible locations for near-surface water and helps us interpret features formed in past environments. Integrating information about the morphology, chemistry and mineralogy of surface deposits is essential for understanding alteration processes. It requires orbital and surface-based remote sensing of the surface (microns to centimeters) and shallow subsurface (meters to 10s of meters), and direct measurements of sediments and atmospheric boundary layer processes. 7. Investigation: Determine the tectonic history and large-scale vertical and horizontal structure of the regolith and crust, including present activity. This includes, for example, the structure and origin of hemispheric dichotomy. Understanding the tectonic record and the structures within the regolith and crust over large vertical and horizontal scales is crucial for understanding the geologic history as well as the temporal evolution of internal processes. This, in turn, places constraints on release of volatiles from differentiation and volcanic activity and the effect of tectonic structures (faults and fractures in particular) on subsurface hydrology. Determining these structures requires gravity data, deep subsurface sounding (100s of meters to kilometers), detailed geologic and topographic mapping (including impact mapping/studies), and determination of the compositions of surface materials. A seismic network is required to understand the distribution and intensity of current tectonic activity. 8. Investigation: Determine the present state, 3-dimensional distribution, and cycling of water on Mars. Water is an important geologic agent on Mars, influencing most geological processes including the formation of sedimentary, igneous and metamorphic rocks, the weathering of geological materials, and deformation of the lithosphere. Determining the distribution of water in its various phases requires global observations using subsurface sounding and remote sensing, coupled with detailed local and regional sounding and measurements. 9. Investigation: Determine the nature of crustal magnetization and its origin. The magnetization of the Martian crust is only poorly understood from Mars Global Surveyor data, but is intimately related to the geothermal history of the planet. Addressing this problem requires high-resolution (spatial and field strength) mapping of the magnetic field and knowledge of the crustal mineralogy, geothermal gradient, and magnetization of the surface. 10. Investigation: Evaluate the effect of large-scale impacts on the evolution of the Martian crust. Impact are one of the most important of the processes shaping the crust and surface of Mars. A firm understanding of effects of impact impact events (e.g., those producing quasi-circular depressions and basins) on the structural, topographic and thermal history of Mars is a prerequisite for any broad understanding of the Martian crust and surface. Understanding impact effects requires geologic mapping using global topographic data combined with high-resolution images and remote sensing. B. Objective: Characterize the structure, composition, dynamics, and evolution of Mars’ interior (investigations in priority order) Investigating the internal dynamics and structure of Mars contributes to understanding the bulk chemical composition of the planet, the evolution of its crust and mantle, the origin of its magnetic field, and the nature and origin of the minerals that record the field. These are fundamental aspects of Mars that form the basis of comparative planetology. 1. Investigation: Characterize the structure and dynamics of the interior. Understanding the structure and dynamical processes of the mantle and core is fundamental for understanding the origin and evolution of Mars, its surface evolution, and the release of water and atmospheric gasses. For example, the thickness of the crust and the size of the core provide strong constraints on the bulk composition of the planet and the manner in which it differentiated. This investigation requires seismology (e.g., passive and active experiments and understanding of the seismic state of the planet), heat flow, and gravity data 2. Investigation: Determine the origin and history of the magnetic field. Evidence that Mars had a magnetic field early in its history has important implications for its formation and early evolution, as well as for the retention of an early atmosphere and for the shielding of the surface from incoming radiation. The collection of high-precision, high-resolution global, regional, and local magnetic measurements, calibration of the ages of surfaces, and measurements of the magnetic properties of samples are now required. 3. Investigation: Determine the chemical and thermal evolution of the planet. Knowledge of the chemical and thermal evolution places constraints on the composition, quantity, and rate of release of volatiles (water and atmospheric gasses) to the surface. This investigation requires measurements of the internal structure, thermal state, surface composition and mineralogy, and geologic relationships. 4. Investigation: Study the structure, dynamics and composition of Phobos and Deimos. Dynamical arguments suggest that the origin of Phobos and Deimos may be intimately connected with that of Mars itself. The dynamics of their orbits may provide constraints on the structure of Mars’ interior and their composition may provide further clues to its evolution. This investigation would be aimed at understanding if Phobos and Deimos are related to Mars and if so, understanding their properties as constraints on the composition and evolution of Mars. IV. GOAL: PREPARE FOR HUMAN EXPLORATION Robotic missions serve as logical precursors to eventual human exploration of space. In the same way that the Lunar Orbiters, Ranger and Surveyor landers paved the way for the Apollo moon landings, a series of robotic Mars Exploration Program missions is charting the course for future human exploration of Mars. Goal IV of the MEPAG document differs from the previous Goals in that it addresses science and engineering questions specific to increasing the safety, decreasing the cost, and increasing the productivity of human crews on Mars. To address these issues this section describes both the data sets that are to be collected and analyzed (Objective A), and the demonstrations of critical technologies that must be validated in the actual Martian environment (Objective B). Finally, Objective C highlights mission critical atmospheric measurements that will reduce mission risk and enhance overall science return, benefiting all future missions to the planet. No attempt has been made to prioritize these risk mitigation and engineering related measurements since all are important. The 2004 National Vision for Space Exploration provides guidance for a broad range of human and robotic missions to the moon, Mars and destinations beyond. Robotic missions serve as one component of a “system of systems”, the sum of which work together to accomplish the goals of implementing a safe, sustained, and affordable robotic and human program to explore and extend human presence across the solar system and beyond. One of the Vision’s main points is to conduct robotic exploration of Mars to prepare for human exploration, and NASA has adopted a “level zero” requirement to “conduct robotic exploration of Mars to search for evidence of life, to understand the history of the solar system, and to support future human exploration activities.” Specifically, robotic precursor missions would be used in part to acquire and analyze data for the purpose of reducing cost and risk of future human exploration missions, would perform technology and flight system demonstrations for the purpose of reducing cost and risk of future human exploration missions, and would deploy infrastructure to support future human exploration activities. As part of the momentum associated with the 2004 National Vision for Space Exploration, in 2004-2005 MEPAG undertook a major reassessment of the issues associated with preparing for the human exploration of Mars. This work is summarized in the following two documents, which represent analyses of Goal IV Objective A, and Goal IV Objective B, respectively. The logic associated with the investigations and measurements is described in these reports. Beaty, D.W., Snook, K., Allen, C.C., Eppler, D., Farrell, W.M., Heldmann, J., Metzger, P., Peach, L., Wagner, S.A., and Zeitlin, C., (2005). An Analysis of the Precursor Measurements of Mars Needed to Reduce the Risk of the First Human Missions to Mars. Unpublished white paper, 77 p, posted June 2005 by the Mars Exploration Program Analysis Group (MEPAG) at http://mepag.jpl.nasa.gov/reports/index.html. Hinners, N.W., Braun, R.D., Joosten, K.B., Kohlhase, C.E., and Powell, R.W., (2005), Report of the MEPAG Mars Human Precursor Science Steering Group Technology Demonstration and Infrastructure Emplacement (TI) Sub-Group, 24 p. document posted July, 2005 by the Mars Exploration Program Analysis Group (MEPAG) at http://mepag.jpl.nasa.gov/reports/index.html. Objective A. Obtain knowledge of Mars sufficient to design and implement a human mission with acceptable cost, risk and performance.4 Investigations #1A-1D are judged to be of indistinguishable high priority. Investigation 1A. Characterize the particulates that could be transported to hardware and infrastructure through the air (including both natural Aeolian dust and other materials that could be raised from the martian regolith by ground operations), and that could affect engineering performance and in situ lifetime. Analytic fidelity sufficient to establish credible engineering simulation labs and/or performance prediction/design codes on Earth is required. Measurements a. A complete analysis, consisting of shape and size distribution, mineralogy, electrical and thermal conductivity, triboelectric and photoemission properties, and chemistry (especially chemistry of relevance to predicting corrosion effects), of samples of regolith from a depth as large as might be affected by human surface operations. Note #1: For sites where air-borne dust naturally settles, a bulk regolith sample is sufficient—analysis of a separate sample of dust filtered from the atmosphere is desirable, but not required. Note #2: Obtaining a broad range of measurements on the same sample is considerably more valuable than a few measurements on each of several samples (this naturally lends itself to sample return). Note #3: There is not consensus on adding magnetic properties to the list of measurements. b. Characterize at least one regolith deposit with fidelity sufficient to establish credible engineering simulation labs and/or software codes on Earth to solve engineering problems related to differential settlement of the regolith, and plume/regolith interactions (see Note #4). 1. For one site on Mars (see Note #5), measure the following properties of the regolith as a function of depth to 1 meter:
2. Repeat the above measurements at a second site in different geologic terrane: c. The same measurements as in a) on a sample of air-borne dust collected during a major dust storm. d. Subsets of the complete analysis described in a), and measured at different locations on Mars (see Note #2). For individual measurements, priorities are: i. shape and size distribution and mineralogy ii. electrical iii. Chemistry Note #4. Because there is a large engineering lead-time required to solve the geotechnical problems, these data must be obtained early in the precursor program. Note #5. These measurements should be made in a competent regolith deposit as opposed to loose drift material (cohesionless sand dunes), as landing is expected to attempt to avoid the looser material. Also, if mission planners would select high latitude polar deposits for a human landing site, geotechnical data will be required from a representative location of those deposits. These measurements should include polarity and magnitude of charge on individual dust particles suspended in the atmosphere and concentration of free atmospheric ions with positive and negative polarities. Measurement should be taken during the day in calm conditions representative of nominal Extra Vehicular Activity (EVA) excursions. Investigation 1B. Determine the atmospheric fluid variations from ground to >90 km that affect EDL and TAO including both ambient conditions and dust storms. Measurements:
Particular emphasis on measurements between 0-20 km to quantify boundary layer wind and turbulence and 30-60 km where vehicle dynamic pressure is large.
Note particular emphasis on measurements between 0-20 km to quantify boundary layer wind and turbulence and 30-60 km where vehicle dynamic pressure is large.
Note #6: We have not reached agreement on the minimum number of atmospheric measurements described above, but it would be prudent to instrument all Mars atmospheric flight missions to extract required vehicle design and environment information. Our current understanding of the atmosphere comes primarily from orbital measurements, a small number of surface meteorology stations and a few entry profiles. Each landed mission to Mars has the potential to gather data that will significantly improve our models of the martian atmosphere and its variability. It is thus desired that each opportunity be used to its fullest potential to gather atmospheric data. Reconstructing atmospheric dynamics from tracking data is useful but insufficient. Properly instrumenting entry vehicles is required. 1C. Determine if each martian site to be visited by humans is free, to within acceptable risk standards, of biohazards that may have adverse effects on humans and other terrestrial species. Sampling into the subsurface for this investigation must extend to the maximum depth to which the human mission may come into contact with uncontained martian material. Measurements:
Note #7: To achieve the necessary confidence, this would require sample return and analyses in terrestrial laboratories. Note #8: The samples could be collected from any site on Mars that is subjected to wind-blown dust. Note #9: At any site where dust from the atmosphere is deposited on the surface, a regolith sample collected from the upper surface would be sufficient--it is not necessary to filter dust from the atmosphere.
Note #10: It is recommended that a decision on whether human landing sites after the first one require a lander with biological screening abilities be deferred until after Measurement a) has been completed. Investigation 1D. Characterize potential sources of water to support In Situ Resource Utilization (ISRU) for eventual human missions. At this time it is not known where human exploration of Mars may occur. However, if ISRU is determined to be required for reasons of mission affordability and/or safety, then the following measurements for water with respect to ISRU become necessary (these options cannot be prioritized without applying constraints from mission system engineering, ISRU process engineering, and geological potential): Measurement Options:
Measurements for water at other locations and depths are not precluded but require further scientific measurements and/or analysis to warrant consideration. This option would specifically include accessing a deep aquifer. The following investigations are listed in descending priority order. Investigation 2. Determine the possible toxic effects of martian dust on humans. Measurements: a. For at least one site, assay for chemicals with known toxic effect on humans. Of particular importance are oxidizing species such as CrVI. (May require Mars Sample Return (MSR)). b. Fully characterize soluble ion distributions, reactions that occur upon humidification and released volatiles from a surface sample and sample of regolith from a depth as large as might be affected by human surface operations. c. Analyze the shapes of martian dust grains sufficient to assess their possible impact on human soft tissue (especially eyes and lungs). d. Determine if martian regolith elicits a toxic response in an animal species that are surrogates for humans.
Investigation 4. Determine the processes by which terrestrial microbial life, or its remains, is dispersed and/or destroyed on Mars (including within ISRU-related water deposits), the rates and scale of these processes, and the potential impact on future scientific investigations. Measurements:
Investigation 5. Characterize in detail the ionizing radiation environment at the martian surface, distinguishing contributions from the energetic charged particles that penetrate the atmosphere, secondary neutrons produced in the atmosphere, and secondary charged particles and neutrons produced in the regolith. Measurements: a. Measurement of charged particles with directionality. Identify particles by species and energy from protons to iron nuclei in the energy range 20-1000 MeV/nuc. b. Measurement of neutrons with directionality. Energy range from 1 keV (or lower) to 100 MeV (or higher). c. Simultaneous with surface measurements, a detector should be placed in orbit to measure energy spectra in Solar Energetic Particle events. Investigation 6. Determine traction/cohesion in martian regolith (with emphasis on trafficability hazards, such as dust pockets and dunes) throughout planned landing sites; where possible, feed findings into surface asset design requirements. Measurements: a. Determine vertical variation in in-situ regolith density within the upper 30 cm for rocky areas, on dust dunes, and in dust pockets to within 0.1 g cm-3. b. Determine variation in in-situ internal angle of friction of regolith for dust dunes and dust pockets to within 1 degree. c. Determine regolith cohesion for rocky areas, dust dunes and in dust pockets to within 0.1 kN m-2.
For basic design of mobility systems, the following measurements are needed (not just at the dust pockets and dunes, but also on the consolidated regolith surfaces where we may do most of the driving): (i) rolling resistance (the torque that regolith applies to a rolling wheel while driving), (ii) traction test (torque required to spin a wheel while the rover is held stationary), and (iii) shape/size of the resulting wheel ruts while driving normally. Note #11: These three things would probably be measured routinely on all Mars rovers. Note #12: ISRU excavation could require hauling larger loads (regolith/ice payload) than what we have ever hauled in the past. Therefore they will need these data to properly design wheels and chases (e.g., rover and large structure mobility systems), avoiding energy-wasteful designs or risk of getting bogged down. Investigation 7. Determine the meteorological properties of dust storms at ground level that affect human occupation and EVA. Measurements:
Table 1. Summary of Location Considerations for high-priority human Precursor Investigations.
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