Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
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8 Question 5: Solid Body Interiors and Surfaces
8 Question 5: Solid Body Interiors and Surfaces
Pages 219-245
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From page 220... ...
The thermal evolution of icy bodies is controlled by melting of the ice phases and alteration of silicate minerals to clays, resulting in segregation of an ice-rich surface layer and sometimes a subsurface ocean. Melting is driven either by decay of short-lived radionuclides (which are most abundant in icy satellites that formed earliest)
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From page 221... ...
and icy bodies. For terrestrial bodies, the core is the metallic central region, with the exterior mantle being silicate; for icy bodies, it is the rock + metal central region, with the exterior mantle being ice (for consistency, Io is categorized as an icy body but with an ice fraction of zero)
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From page 222... ...
or Discrete Regions Occur in Solid Bodies, What Are Their Characteristics, Where Are They, and How Long Do They Persist? The existence, locations, and compositional variations of liquid layers and discontinuous liquid regions (e.g., molten cores, partly melted magma source regions, brine lakes, subsurface oceans)
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From page 223... ...
At the surface, tectonic activity and eruptions are a consequence of internal evolution or external tidal forces. Below the surface, liquid metal cores generate magnetic fields whose histories reflect changes in the temperature and composition of the core and overlying mantle.
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From page 225... ...
These liquid layers can be responsible for generating magnetic fields and producing fluids that can erupt onto planetary surfaces. Liquid metal cores, partially to totally melted layers in mantles, and subsurface oceans require sufficient heat to melt and remain molten, while crystallization of these layers will produce latent heat.
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From page 226... ...
Studying the composition of materials exposed on planetary surfaces, such as changing compositions of volcanic products erupted on the surfaces of rocky bodies and ocean worlds, thus provides an opportunity 2 While cryovolcanism can be regarded as a subset of volcanism, this report draws a distinction between the two processes for clarity. Thus, (cryo)
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From page 227... ...
Q5.3 HOW HAVE SURFACE/NEAR-SURFACE CHARACTERISTICS AND COMPOSITIONS OF SOLID BODIES BEEN MODIFIED BY, AND RECORDED, INTERIOR PROCESSES? Planetary surfaces, the most external portion of the solid body, are influenced by complex physical and chemical processes within the body's interior.
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From page 228... ...
Volcanic eruptions shed light on the internal compositions, temperatures, and degree of processing of subsurface materials on solid bodies without having to directly sample their interiors. Eruptions on planetary bodies are controlled by numerous, interrelated factors, including (but not limited to)
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From page 229... ...
Similarly, understanding emplacement processes is hampered by the difficulty in determining internal flow structures and subtle compositional variations. These issues are particularly problematic on Venus and icy bodies, where an array of unique, likely volcanic landforms have been identified but cannot be fully described, classified, or explained (e.g., Crumpler et al.
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From page 230... ...
As water-rock interactions are only sustainable if fresh rock is available, constraining the timing and duration of water-rock interactions on ocean worlds also provides information on the exposure or production rates of fresh rock surfaces, giving insight into other geological processes. Hydrothermal processes may also be responsible for synthesis of some of the organic compounds on ocean worlds, dwarf planets, and asteroids.
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From page 231... ...
. Titan has modern fluvial activity, but with PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 8-13
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From page 232... ...
These different ices and mixtures of ices create glaciers with distinct physical properties compared to Earth, so further study of such glacial processes is important for understanding and further investigating surface processes and their records on bodies farther out in the solar system. The record of glaciation on icy bodies and dwarf planets remains uncertain, as does the exact composition of the glaciers, and the processes controlling their accumulation, movement, and destruction.
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From page 233... ...
Chemical weathering and alteration of surface materials represent the main way atmospheres and hydrospheres interact chemically with the solid surfaces of planetary bodies, and produce secondary minerals from reactions between minerals and species in atmospheric gases or fluids. The specific secondary minerals formed are determined by the initial mineralogy of the surface, chemical species in the atmosphere or fluid, concentration of gas/fluid species, and the pressure and temperature conditions of the near-surface environment.
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From page 234... ...
Q5.5 HOW HAVE SURFACE CHARACTERISTICS AND COMPOSITIONS OF SOLID BODIES BEEN MODIFIED BY, AND RECORDED, EXTERNAL PROCESSES? Planetary surfaces often retain records of the external environments in which planetary bodies formed and evolved.
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From page 235... ...
Developing a general understanding of how different space weathering processes modify the surfaces of planetary bodies and how those vary with local conditions will help to determine rates of geologic processes, understand duration of surface exposure of materials, understand surface composition, and provide a valuable framework that can be used to better interpret remote sensing observations across the solar system. Q5.5b How Have Impacts Affected Surface and Near-Surface Properties?
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From page 237... ...
● Investigate the role of space weathering processes on airless rocky bodies using high-resolution imaging and spectroscopy of planetary surfaces coupled with laboratory studies of representative/analog materials and laboratory analyses of returned samples. ● Determine how small bodies (asteroids and comets)
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From page 238... ...
Other proposed regions of convection include the Sputnik Planitia basin on Pluto, where a cellular floor structure is proposed to form from localized convection in a kilometers-thick surface nitrogen ice sheet, and a similar process may occur in Triton's so-called cantaloupe terrain in the geologic past. Convection and crustal recycling on the icy bodies is poorly understood.
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From page 239... ...
For icy bodies in particular, tectonic processes can illuminate the evolution of their oceans. Fractures may transport materials from subsurface oceans, or other extensive fluid pockets within these worlds, to their surfaces.
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From page 240... ...
. The dearth of in situ seismological investigations on Venus, ocean worlds and dwarf planets, and in many cases, the lack of global, high resolution imagery, limits our ability to tie tectonic activity and deformation to processes occurring in their interiors.
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From page 241... ...
Regolith formation occurs on icy bodies by various processes; for instance, when unconsolidated, icy material is emplaced on their surfaces as a result of impact cratering and, in the case of Enceladus, plume eruptions. Because active regolith formation may erase craters and mute surface topography on ice-rich worlds, constraining the composition and thickness of these unconsolidated layers, as well as the rate at which these layers form, allow us to place improved constraints on the evolution of dwarf planet and satellite surfaces.
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From page 242... ...
SUPPORTIVE ACTIVITIES FOR QUESTION 5 ● Measure optical constants of the range of materials expected in the solar system under relevant pressure and temperature conditions (from Venus to airless icy satellites) to serve as the basis by which we constrain the compositions of planetary surfaces from remote sensing data.
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From page 244... ...
2016. Space weathering on airless bodies.
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