Vision and Voyages for Planetary Science in the Decade 2013-2022 (2011) / Chapter Skim
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5 The Inner Planets: The Key to Understanding Earth-Like Worlds
5 The Inner Planets: The Key to Understanding Earth-Like Worlds
Pages 111-136
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From page 111... ...
The planetary habitats theme includes the question, Did Mars or Venus host ancient aqueous environments conducive to early life, and is there evidence that life emerged? The workings of the solar systems theme includes two questions that can be answered by the study of the inner planets.
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From page 112... ...
The goals for research concerning the inner planets for the next decade are threefold: • Understand the origin and diversity of terrestrial planets. How are Earth and its sister terrestrial planets unique in the solar system, and how common are Earth-like planets around other stars?
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From page 113... ...
Key questions, such as those concerning the development and evolution of life and the intricacies of planetary climate change, can only be formulated and addressed by building this base of knowledge. Fundamental objectives associated with the goal of understanding the origin and diversity of terrestrial planets include the following: • Constrain the bulk composition of the terrestrial planets to understand their formation from the solar nebula and controls on their subsequent evolution; • Characterize planetary interiors to understand how they differentiate and dynamically evolve from their initial state; and • Characterize planetary surfaces to understand how they are modified by geologic processes.
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From page 114... ...
Future investigations and measurements should include the development of improved understanding of the various types of rock and regolith making up the crusts and mantles of the inner planets, through remote sensing of Mercury's crust, in situ investigation of Venus's crust, and sample return of crust and mantle materials from the Moon. Key geophysical objectives include the characterization of the Moon's lower mantle and core and the development of an improved understanding of the origin and character of Mercury's magnetic field.
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From page 115... ...
Characterize Planetary Interiors to Understand How They Differentiate and Dynamically Evolve from Their Initial State Knowledge of the internal structure of the terrestrial planets is key to understanding their histories after accretion. Differentiation is a fundamental planetary process that has occurred in numerous solar system bodies.
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From page 116... ...
and over what timescales? Future Directions for Investigations and Measurements Advancing the understanding of the internal evolution of the inner planets can be achieved through research and analysis activities as well as by data from new missions at the Moon, Mercury, and Venus.
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From page 117... ...
The diversity of terrains observed by MESSENGER suggests a complex evolution, including extensive tectonism and young volcanism and pyroclastic activity.14,15,16 Important Questions Some important questions concerning the characterization of planetary surfaces to understand how they are modified by dynamic geologic processes include the following: • What are the major surface features and modification processes on each of the inner planets? • What were the sources and timing of the early and recent impact flux of the inner solar system?
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From page 118... ...
Understand the Composition and Distribution of Volatile Chemical Compounds To address objectives relating to the composition and distribution of volatile chemical compounds, it is crucial to improve the understanding of the sources, sinks, and physical states of water and of chemical compounds containing hydrogen, carbon, oxygen, sulfur, phosphorus, and nitrogen on and in the inner planets (including Mars) , as functions of time and position in the solar system.
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From page 119... ...
• How are planetary magnetic fields initiated and maintained? Future Directions for Investigations and Measurements Progress can be made in understanding how internal processes affect planetary habitability through focused measurements and research that "follow the volatiles" from the interiors, to the surfaces, to escape from the atmospheres of the inner planets.
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From page 120... ...
Future Directions for Investigations and Measurements Fundamental models of delivery and loss of volatiles relevant for understanding how processes external to a planet can enable or thwart life and prebiotic chemistry can be constrained by investigation of the rates of loss of volatiles from planets to interplanetary space, in terms of solar intensity, gravity, magnetic-field environment, and atmospheric composition. Also key are the characterization of reservoirs of volatiles that feed volatiles onto terrestrial planets after the main phases of planetary accretion (e.g., a late chondritic veneer, heavy bombardment)
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From page 121... ...
Fundamental objectives on the path to understanding the processes that control climate on Earth-like planets include the following: • Determine how solar energy drives atmospheric circulation, cloud formation, and chemical cycles that define the current climate on terrestrial planets; • Characterize the record of and mechanisms for climate evolution on Venus, with the goal of understanding climate change on terrestrial planets, including anthropogenic forcings on Earth; and • Constrain ancient climates on Venus and search for clues into early terrestrial planet environments so as to understand the initial conditions and long-term fate of Earth's climate. Subsequent sections examine each of these objectives in turn, identify critical questions to be addressed, and suggest future investigations and measurements that could provide answers.
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From page 122... ...
Recent results for the other inner planets have placed better constraints on rates and mechanisms of volatile loss (e.g., MESSENGER spacecraft data on Mercury's exosphere and Venus Express SPICAV results for Venus hydrogen and oxygen loss)
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From page 123... ...
Constrain Ancient Climates on Venus and Search for Clues into Early Terrestrial Planet Environments So As to Understand the Initial Conditions and Long-Term Fate of Earth's Climate Planetary exploration provides unique opportunities to study the most ancient or primordial climates of the terrestrial planets. By establishing the early climate conditions on Venus and Mars, finding clues on the Moon to the earliest terrestrial environment, and characterizing the primordial impact environment throughout the inner solar system, the initial conditions that led eventually to the current climate systems of Earth and the other terrestrial planets can be determined.
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From page 124... ...
INTERCONNECTIONS Connections with Other Solar System Bodies The processes that occur in the atmospheres, surfaces, and interiors of the inner planets are governed by the same principles of physics and chemistry that govern the processes found on other solar system bodies. Comparing and contrasting the styles of past and present interior dynamic, volcanic, tectonic, aeolian, mass wasting, impact, and atmospheric processes can provide significant insight into such processes.
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From page 125... ...
Studies of the origin and evolution of volatiles on the terrestrial planets, including loss of water from Venus and Mars and the effects of early planetary magnetic fields and variation in the solar wind over time are critical to our understanding of where environments might have existed for the development of life. Although recent orbital and rover missions on Mars have identified early environments on that planet that may have fostered life, there is no evidence from the low-resolution images from past missions of the existence of early terrains on Venus.
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From page 126... ...
New capabilities for in situ age dating are of particular importance, as they can help to provide constraints on models of the surface and interior evolution of all the terrestrial planets. ADVANCING STUDIES OF THE INNER PLANETS Previously Recommended Missions A series of National Research Council (NRC)
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From page 127... ...
Achieving all of these objectives represents a flagship-class investment, 29 but achieving a majority is considered feasible in the New Frontiers program.30 In the 2003 planetary science decadal survey, the long-term goal was extraction and return to Earth of samples (solid and gas) from the Venus surface, clearly a flagship-class mission, and VISE was considered in terms of its contribution to this sample return.
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From page 128... ...
A robotic lunar sample return mission has extensive "feed-forward" to future sample return missions from other locations on the Moon as well as Mars and other bodies in the solar system. New Missions: 2013-2022 Flagship Class The most recent report from the Venus Exploration Analysis Group (VEXAG)
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From page 129... ...
SOURCE: Courtesy of David Grinspoon and Carter Emmart. Venus Climate Mission The Venus Climate Mission will greatly improve our understanding of the current state and dynamics and evolution of the strong carbon dioxide greenhouse climate of Venus, providing fundamental advances in the understanding of and ability to model climate and global change on Earth-like planets.
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From page 130... ...
New Frontiers Class Important contributions can be made by a lunar geophysical network (LGN) to the goals for the study of the inner planets.
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From page 131... ...
• Determine the size of structural components (e.g., crust, mantle, and core) making up the interior of the Moon, including their composition and compositional variations, to estimate bulk lunar composition and how it relates to that of Earth and other terrestrial planets, how the Earth-Moon system was formed, and how planetary compositions are related to nebular condensation and accretion processes.
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From page 132... ...
(See Box 5.2.) • Technology development -- The development of technology is critical for future studies of the inner planets.
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From page 133... ...
Elements of an inner planets roadmap are outlined below. For Mercury, the current MESSENGER mission will provide a wealth of new information that could further redefine our understanding of the planet and modify priorities for future missions.
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From page 134... ...
NOTES AND REFERENCES 1 . The term inner planets is used here to refer to Mercury, Venus, and the Moon, whereas the term terrestrial planets is used to refer to Earth, Mercury, Venus, Mars, and the Moon.
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From page 135... ...
Earth and Planetary Science Letters 285(3-4)
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From page 136... ...
26 . See, for example, National Research Council, Strategy for Exploration of the Inner Planets 1977-1987, National Academy of Sciences, Washington, D.C., 1978.
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