Vision and Voyages for Planetary Science in the Decade 2013-2022 (2011) / Chapter Skim
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6 Mars: Evolution of an Earth-Like World
6 Mars: Evolution of an Earth-Like World
Pages 137-174
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From page 137... ...
The spacecraft exploration of Mars began in 1965 with an exploration strategy of flybys, followed by o rbiters, landers, and rovers with kilometers of mobility. This systematic investigation has produced a detailed knowledge of the planet's character, including global measurements of topography, geologic structure and processes, surface mineralogy and elemental composition, the near-surface distribution of water, the intrinsic and r emanant magnetic field, gravity field and crustal structure, and the atmospheric composition and time-varying state (Figure 6.1)
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From page 138... ...
In addition, the program has produced missions that support one another both scientifically and through infrastructure, with orbital reconnaissance and site selection, data relay, and critical event coverage significantly enhancing the quality of the in situ missions.11,12,13 Finally, this program has allowed the Mars science
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From page 139... ...
Mustard, and J.-P. Bibring, Discovery of Diverse Martian Aqueous eposits D from Orbital Remote Sensing, presentation from the Curation and Analysis Planning Team for Extraterrestrial Materials Workshop on Ground Truth from Mars, Science Payoff from a Sample Return Mission, April 21-23, 2008, Albuquerque, New Mexico, available at http://www.lpi.usra.edu/captem/msr2008/presentations/.
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From page 140... ...
community to construct a logical series of missions each of which is modest in scope and systematically advances our scientific understanding of Mars. Over the past decade the Mars science community, as represented by the Mars Exploration Program Analysis Group (MEPAG)
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Mars is central to the planetary habitats theme, which also includes two questions that are key components of the scientific exploration of Mars -- What were the primordial sources of organic matter, and where does organic synthesis continue today? and, Beyond Earth, are there modern habitats elsewhere in the solar system with n ecessary conditions, organic matter, water, energy, and nutrients to sustain life, and do organisms live there now?
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From page 142... ...
Therefore, the committee's specific objectives for pursuing the life goal are as follows: • Assess the past and present habitability of Mars, • Assess whether life is or was present on Mars in its geochemical context, and • Characterize carbon cycling and prebiotic chemistry. Subsequent sections examine each of these objectives in turn, identifying critical questions to be addressed and future investigations and measurements that could provide answers.
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From page 143... ...
.26,27,28 Early Mars also witnessed extensive volcanism and high impact rates. The formation of large impact basins likely developed hydrothermal systems and hot springs that might have sustained locally habitable environments.29,30,31 Since approximately 3.5 billion years ago, rates of weathering and erosion appear to have been very low, and the most characteristic fluvial features are outflow channels formed by the catastrophic release of near-surface water.32 Groundwater is likely to be stable at greater depths, and it might sustain habitable environments.
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From page 144... ...
Analyses of returned samples in Earth-based laboratories are essential in order to establish the highest confidence in any potential martian biosignatures and to interpret fully the habitable environments in which they were formed and preserved.36,37,38,39,40 Key technological developments for surface exploration and sampling include modest-size rovers capable of selecting samples and documenting their context. These rovers should include imaging and remote sensing spectroscopy adequate to establish local geologic context and to identify targets.
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2009. Mars exploration, comparative planetary history, and the promise of Mars Science Labora tory, Nature Geoscience 2:1-3.
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45,46,47,48 Assess Whether Life Is or Was Present on Mars in Its Geochemical Context and Characterize Carbon Cycling and Prebiotic Chemistry Assessing whether life is or was present on Mars will include characterizing complex organics, the spatial distribution of chemical and isotopic signatures, and the morphology of mineralogic signatures, and identifying temporal chemical variations requiring life. Characterizing the carbon cycle will include determining the distribution and composition of organic and inorganic carbon species; characterizing the distribution and composition of inorganic carbon reservoirs through time; characterizing the links between carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur; and characterizing the preservation of reduced carbon compounds on the near-surface through time.
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From page 147... ...
Understanding the current climate includes investigating the processes controlling the present distributions of water, carbon dioxide, and dust; determining the production and loss, reaction rates, and global distribution of key photochemical species; and understanding the exchange of volatiles and dust between surface and atmospheric reservoirs. Understanding past climates includes determining how the composition of the atmosphere evolved to its present state, what the chronology of compositional variability is, and what record of climatic change is expressed in the surface stratigraphy and morphology.
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From page 148... ...
Recent observations from Mars Global Surveyor, Mars Reconnaissance Orbiter, Mars Express, and Phoenix have also shown puzzling structures in the vertical profiles of airborne dust, unexpected distributions of water vapor, and surprising precipitating ice clouds. 51,52 The carbon dioxide cycle itself is more complex than anticipated, with a condensation phase controlled by atmospheric precipitation, subsurface heating, and noncondensable gas enrichment and with a sublimation phase characterized by the formation of high-velocity carbon dioxide vents that erupt sand-size grains in jets able to form spots and control the polar cap albedo.53 The residual carbon dioxide ice cap near the south pole has been found to lie on a water-ice substrate but appears to be only a few meters thick.54,55 This discovery is surprising, because models suggest that this ice cap should either grow thick or disappear on a decadal timescale, unless it is the product of climate variations on such timescales; the discovery is also surprising because the thinness of the ice cap indicates that the readily available carbon dioxide reservoir may be smaller than previously thought.
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MARS: EVOLUTION OF AN EARTH-LIKE WORLD 149 FIGURE 6.4 Examples of recent climate changes on Mars as seen in the surface morphology. The image shows an area 3.05 km wide.
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These investigations include the detection and mapping of possible trace gases and key isotopes, with the highest sensitivity achievable, as a window into underlying geological and possible biological activity -- to be addressed by the ESA-NASA Mars Trace Gas Orbiter now under development. Fundamental advances in our understanding of modern climate would come from a complete determination of the three-dimensional structure of the martian atmosphere, from the surface boundary layer to the exosphere.
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From page 151... ...
It will also be crucial to investigate the physical and chemical record constraining past climates, particularly regarding the polar layered deposits.78 In order to follow up on scientific results and discoveries from the Phoenix and Mars Reconnaissance Orbiter missions, an in situ analysis of laterally or vertically resolved measurements of grain size, dust content, composition, thickness and extent of layers, elemental and isotopic ratios relevant to age (e.g., deuterium/hydrogen) and astrobiology (CHNOPS)
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From page 152... ...
indicate that large hot spots likely played a significant role in the geologic, tectonic, and thermal evolution of the planet, as well as in the surface history through the release of acidic volatiles to the martian atmosphere,104 the transport of aqueous fluids over immense distances, and the formation of hydrothermal deposits.105 It is likely that the cessation of the magnetic field had a major effect on the evolution of the early martian atmosphere.106,107 Thus, the history of the interior is closely connected to the atmosphere, surface mineralogy, and potential habitability, and the measurement of interior properties, identification of possible mantle phase transformations, and petrological and geochemical studies of martian meteorites would provide crucial constraints on magmatic processes on early Mars. Recent Mars (post approximately 3.0 billion years)
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MARS: EVOLUTION OF AN EARTH-LIKE WORLD 153 FIGURES 6.5 Top: Examples of the record of martian mineralogic diversity accessible from a surface rover mission. Bottom: Quartz-rich subsurface material exposed in the rover's tracks.
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From page 154... ...
Wiseman, R.E. Arvidson, et al., A synthesis of martian aqueous mineralogy after one Mars year of observations from the Mars Reconnaissance Orbiter, Journal of Geophysical Research 114:E00D06, 2009, doi: 10.1029/2009JE003342, copyright 2009 American Geophysical Union, modified by permission of American Geophysical Union.
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From page 155... ...
Future Directions for Investigations and Measurements Key investigations to advance our understanding of geologic processes that have governed Mars's evolution include understanding the origin and nature of the sedimentary units by applying physical and geochemical models, remote and in situ observations of diverse suites of sedimentary materials on Mars, and laboratory investigations of Mars analog materials to study the formation, transport, and deposition of sedimentary materials by fluvial, aeolian, impact, and mass wasting processes. Major advances will come from the investigation of the petrologic, mineralogic, isotopic, and geochronologic properties of rock suites in returned martian samples, martian meteorites, and Mars analog materials in order to understand environmental conditions and habitability over time; the history and timing of core separation and differentiation; past tectonic processes; Mars's past and present geophysical properties; the bulk, mantle, and core compositions; and the relationship between martian meteorites and igneous rocks on Mars's surface.
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From page 156... ...
Mars is in the Sun's "habitable zone," it likely had liquid water at some points in the past, and it might have had a thicker atmosphere that protected the prebiotic and biotic material from radiation. Mars today contains the essential ingredients to support and sustain life, and the geologic record shows numerous promising ancient habitable environments.
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From page 157... ...
,124,125,126,127,128 several major recent reports by MEPAG,129,130,131 and a significant recent contribution by the International Mars Exploration Working Group.132 Numerous white papers submitted to the NRC decadal survey indicated substantial community support by way of signatories and addressed the importance and significance of Mars Sample Return as the keystone of future Mars exploration.
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It is these aqueous and altered materials that will provide the opportunity to study aqueous environments and potential prebiotic chemistry. Two approaches to the study of martian materials exist -- that using in situ measurements and that employing returned samples.
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The encapsulation of at least some samples must retain any released volatile components.11,12 Technical Implementation and Feasibility A three-element, step-by-step sample return campaign would reduce scientific, technical, and cost risks. It would build on technologies developed over the past decade of Mars exploration, although major technical challenges remain that must be addressed in a technology development effort that would be an integral part of the sample return campaign.
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From page 160... ...
Thus, a critical next step toward answering these questions would be provided through the analysis of carefully selected samples from geologically diverse and wellcharacterized sites that are returned to Earth for detailed study. Existing scientific knowledge of Mars makes it possible to select a site from which to collect an excellent suite of rock and soil samples to address the life and habitability questions, and the technology to implement the sample return campaign exists, or will be developed -- including required entry, descent, and landing (EDL)
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7 Mars Exploration Program Analysis Group Next Decade Science Analysis Group.
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TECHNOLOGY DEVELOPMENT As Mars exploration moves toward sample return, surface networks, and sophisticated in situ analysis, it will require a suite of technology development efforts, primarily focused in the areas of sample acquisition and handling, Mars ascent, and orbital rendezvous. Improvements in instrumentation, ground-based infrastructure, and data analysis are also critical to the long-term success of the Mars exploration program.
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From page 163... ...
The recommendations of the NRC's 2002 report The Quarantine and Certification of Martian Samples142 may need to be examined and updated as necessary based on the current plans for the nature and quantity of the returned samples. Supporting Laboratory and Theoretical Studies Relevant laboratory studies have in the past been deferred, due largely to their expense, but they are essential for supporting sample return.
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From page 164... ...
A critical next step toward answering these questions will be provided through the analysis of carefully selected samples from geologically diverse and wellcharacterized sites that are returned to Earth for detailed study using a wide diversity of laboratory techniques. Therefore, the highest-priority missions for Mars in the coming decade are the elements of the Mars Sample Return campaign -- the Mars Astrobiology Explorer-Cacher to collect and cache samples, followed by the Mars Sample Return Lander and the Mars Sample Return Orbiter (Figure 6.7)
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From page 165... ...
The cache systems will be designed to prevent cross-contamination between samples, prevent exposure to the martian atmosphere, keep the samples within the temperature range that they experienced prior to collection, and preserve the samples in this condition for up to 20 years. Mars Sample Return Lander The Mars Sample Return Lander (MSR-L)
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From page 166... ...
Mars Returned-Sample-Handling Facility The Mars returned-sample-handling facility will meet the planetary protection requirements and will be based on practices and procedures at existing biocontainment laboratories, NASA's Lunar Sample Facility, and pharmaceutical laboratories. Mars Trace Gas Orbiter The Mars Trace Gas Orbiter is currently conceived as a joint ESA-NASA collaboration to study the temporal and spatial distribution of trace gases, atmospheric state, and surface-atmosphere interactions on Mars.
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From page 167... ...
Examples of potential Mars missions that could be performed in the Discovery program, in no priority order, include the following: • A one-node geophysical pathfinder station, • A polar science orbiter, • A dual satellite atmospheric sounding and/or gravity mapping mission, • An atmospheric sample-collection and Earth return mission, • A Phobos/Deimos surface exploration mission (see Chapter 4) , and • An in situ aerial mission to explore the region of the martian atmosphere and remanant magnetic field that is not easily accessible from orbit or from the surface.
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From page 168... ...
2006. Science Analysis of the November 3, 2005 Version of the Draft Mars Exploration Program Plan.
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White paper submitted to the Planetary Science Decadal Survey, National Research Council, Washington, D.C. 14 Mars Exploration Program Analysis Group (MEPAG)
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Working Group. Mars Exploration Program Analysis Group, Jet Propulsion Laboratory, Pasadena, Calif.
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White paper submitted to the Planetary Science Decadal Survey, . National Research Council, Washington, D.C.
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2008. Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument.
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White paper submitted to the Planetary Science Decadal Survey, National Research Council, Washington, D.C.
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A Scientific Rationale for a Mars Sample-Return Campaign as the Next Step in Solar System Exploration. White paper submitted to the Planetary Science Decadal Survey, National Research Council, Washington, D.C.
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