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Pages 219-245

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From page 219...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 219 directly onto the surface, although they have been suggested to be more common on some planets and planetesimals (e.g., eucrites on Vesta)
From page 220...
... 220 ORIGINS, WORLDS, AND LIFE Q5.3d Where and How Are Surfaces Modified by Hydrothermal/Geothermal Processes? Materials that have been mineralogically or geochemically altered by hydrothermal processes in the interior can be exposed on the surface, thus modifying its composition.
From page 221...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 221 Q5.4 HOW HAVE SURFACE CHARACTERISTICS AND COMPOSITIONS OF SOLID BODIES BEEN MODIFIED BY, AND RECORDED, SURFACE PROCESSES AND ATMOSPHERIC INTERACTIONS? The surfaces of solid bodies record evidence of atmospheric interaction, and thereby provide information about how the atmosphere may have evolved through time (see also Question 6, Chapter 9)
From page 222...
... 222 ORIGINS, WORLDS, AND LIFE related glacial activity may be occurring on Triton and on other dwarf planets in the Kuiper belt. 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.
From page 223...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 223 weathering is on Mars, and what it can reveal about the presence (or absence) of surface water or groundwater, and the compounds dissolved into that water through Mars's history.
From page 224...
... 224 ORIGINS, WORLDS, AND LIFE Charged particles (from the solar wind, and/or the relevant planetary magnetosphere for planetary satellites) collide with individual regolith grains and lose energy as they are implanted into grains, breaking bonds.
From page 225...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 225 Developing a general understanding of how different space weathering processes modify the surfaces of p­ lanetary 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?
From page 226...
... 226 ORIGINS, WORLDS, AND LIFE (Khurana et al.
From page 227...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 227 Q5.6 WHAT DRIVES ACTIVE PROCESSES OCCURRING IN THE INTERIORS AND ON THE SURFACES OF SOLID BODIES? Activity is present on the surfaces and in the interiors of both rocky and icy bodies throughout the solar system.
From page 228...
... 228 ORIGINS, WORLDS, AND LIFE planet's history. Despite abundant evidence for the work of volcanism in shaping the surfaces of the terrestrial planets and our own Moon, only Io is demonstrably volcanically active, although Venus has provided us with tantalizing hints of present-day volcanic eruptions.
From page 229...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 229 FIGURE 8-4  Frequency of quakes as a function of size for different bodies. No seismometer has been placed on Europa.
From page 230...
... 230 ORIGINS, WORLDS, AND LIFE weather regolith particles through formation of nanophase iron, also known as space weathering (Q5.5a)
From page 231...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 231 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.
From page 232...
... 232 ORIGINS, WORLDS, AND LIFE Jolliff, B.L., S.A. Wiseman, S.J.
From page 233...
... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 233 Stähler, S.C., A
From page 234...
... Q6 PLATE:  A view of Venus's atmosphere in the ultraviolet from the Akatsuki mission in 2016. Venus's north pole is to the top in this image.
From page 235...
... 9 Question 6: Solid Body Atmospheres, Exospheres, Magnetospheres, and Climate Evolution What establishes the properties and dynamics of solid body atmospheres and exospheres, and what governs material loss to and gain from space and exchange between the atmosphere and the surface and interior? Why did planetary climates evolve to their current varied states?
From page 236...
... 236 ORIGINS, WORLDS, AND LIFE FIGURE 9-1  Overview of atmospheric characteristics for the solid planets and moons discussed in this chapter. Top panel: Bodies with collisionless exospheres only.
From page 237...
... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 237 These are but a few of a fascinating array of questions that remain to be answered about the atmospheres of the planets and moons in today's solar system. The committee highlights the major outstanding issues below.
From page 238...
... 238 ORIGINS, WORLDS, AND LIFE the young Sun would have made this process particularly important to atmospheric evolution in the first few hundred million years after the planets formed (Lammer et al.
From page 239...
... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 239 early atmosphere, and this may help explain why Mars's early climate was relatively warm despite the faintness of the young Sun (Ramirez et al.
From page 240...
... 240 ORIGINS, WORLDS, AND LIFE • Develop physical and chemical constraints on early atmosphere–interior exchange by performing laboratory experiments on volatile partitioning in silicate melts, meteorite shock chemistry, and related phenomena.
From page 241...
... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 241 during the ensuing Proterozoic and Phanerozoic eons is a research topic of great interest to astrobiologists because it is poorly understood and because it is relevant to the question of whether O2 is a good biomarker on extrasolar planets (see Question 12, Chapter 15)
From page 242...
... 242 ORIGINS, WORLDS, AND LIFE between samples of ancient Mars (in returned rock samples and meteorites) and the present-day atmosphere provides information on atmospheric source and sink processes over time.
From page 243...
... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 243 • Constrain the timing of martian climate transitions by performing geochronological dating of samples from multiple locations on the planet's surface. • Constrain atmospheric evolution processes on Mars by returning samples of the atmosphere to Earth of sufficient concentration and fidelity to allow noble gas abundance and isotopic fractionation to be measured.
From page 244...
... 244 ORIGINS, WORLDS, AND LIFE FIGURE 9-3  Processes influencing solid body collisional atmospheres, including interior-surface-atmosphere and solar environment interactions. Note that the relative heights of where processes are shown to occur are not drawn to scale.
From page 245...
... QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, AND CLIMATE EVOLUTION 245 angular-momentum gradient. Yet while mechanisms for driving this have been proposed, most of the atmospheric waves involved have not been observed.

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