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From page 192... ... 192 ORIGINS, WORLDS, AND LIFE One of the arguments against the LHB is that the Imbrium basin could have distributed ejecta across much of the lunar nearside, and thus be dominating the observed impact record from the Apollo samples (which are all from the lunar nearside, potentially contaminated by Imbrium) Read the entire page →
From page 193... ... QUESTION 4: IMPACTS AND DYNAMICS 193 this type of investigation is to obtain material that can be placed in geologic context; ages derived from lunar or martian meteorites are useful but cannot be fully exploited because they have an unknown provenance. Additional pathways to enhance current knowledge would be to obtain robust techniques for measuring planetary crater populations accurately, improving our understanding of how small body populations evolve and the impact cratering process itself, and establishing independent constraints on outer solar system chronologies. Read the entire page →
From page 194... ... 194 ORIGINS, WORLDS, AND LIFE problem for planetary satellites stems from how to interpret the contributions from impactors that orbit the planet (planetocentric) , rather than the Sun. Read the entire page →
From page 195... ... QUESTION 4: IMPACTS AND DYNAMICS 195 With that said, though, a good impact flux model will still leave us with challenges in estimating absolute surface ages. For example, as discussed below, comets striking giant planet satellites often produce enormous ejecta showers, which in turn produce numerous secondary and sesquinary craters. Read the entire page →
From page 196... ... 196 ORIGINS, WORLDS, AND LIFE As we improve our understanding of the formation and evolution of planetary bodies, we continue to dis cover that collisions were often -- although not always -- responsible for major planetary-scale events. One of the most poignant examples is the formation of the Earth–Moon system (see Question 3, Chapter 6) Read the entire page →
From page 197... ... QUESTION 4: IMPACTS AND DYNAMICS 197 Q4.3b How Do Impacts Affect Surface and Near-Surface Properties of Solar System Worlds? Impacts modify surface morphologies on planetary bodies (see Q5.5b) Read the entire page →
From page 198... ... 198 ORIGINS, WORLDS, AND LIFE FIGURE 7-2 Topographic perspective views of planetary bodies highlighting many of the large impact events (dashed circles) that have scarred their surfaces and possibly altered their interiors. Read the entire page →
From page 199... ... QUESTION 4: IMPACTS AND DYNAMICS 199 Heating produced by large impact events has also been proposed to explain the putative differences in the interior structures of Ganymede and Callisto (see Questions 5 and 8; Chapters 8 and 11, respectively) Read the entire page →
From page 200... ... 200 ORIGINS, WORLDS, AND LIFE FIGURE 7-3 Top panel: An artist's impression of a complex crater shortly after an impact. The crater is fractured by the impact and filled with impact melt. Read the entire page →
From page 201... ... QUESTION 4: IMPACTS AND DYNAMICS 201 Q4.3e What Exogenic Volatile and Nonvolatile Materials Are Delivered to Planetary Bodies? Impactors deliver materials from one world to another, although the extent to which exogenic materials survive an impact event is not well known. Read the entire page →
From page 202... ... 202 ORIGINS, WORLDS, AND LIFE • Characterize uplifted deeper icy crustal materials and projectile contaminants on icy bodies by obtaining high-resolution spectroscopic identification of mineralogy, crystallinity, and chemistry of impact crater floors, peaks, and ejecta. • Determine the distribution of exogenic materials in comets to identify impactor material conditions by performing high-resolution spectroscopic and imaging observations, and by identifying exogenic materials in sampled materials. Read the entire page →
From page 203... ... QUESTION 4: IMPACTS AND DYNAMICS 203 Last, there is still limited knowledge about how the entire impact process plays out to its end. Impacts consist of multiple physical processes (i.e., contact and compression, excavation, and modification, as well as ejecta formation and deposition, and subsequent relaxation) Read the entire page →
From page 204... ... 204 ORIGINS, WORLDS, AND LIFE • Map structural deformation and characterize impact mechanics in icy target bodies by performing high-resolution imaging of impact crater morphology, with example high-value targets, including the uranian satellites, Europa, Ganymede, and trans-neptunian objects. • Improve crater counts on icy bodies to characterize secondary crater mechanics and constrain smaller projectile populations (especially focused on gaps in the observational record on Europa, Ganymede, in the uranian system, and on additional >100 km trans-neptunian objects) Read the entire page →
From page 205... ... QUESTION 4: IMPACTS AND DYNAMICS 205 Bottke, W.F., D Nesvorný, R.E. Read the entire page →
From page 206... ... 206 ORIGINS, WORLDS, AND LIFE Jewitt, D., H Hsieh, J Read the entire page →
From page 207... ... QUESTION 4: IMPACTS AND DYNAMICS 207 Pajola, M., S Höfner, J.B. Read the entire page →
From page 208... ... Q5 PLATE: A portion of an approximately true-color mosaic of the martian surface near the "Mont Mercou" outcrop, taken by the Curiosity rover in 2021. SOURCE: Courtesy of NASA/JPL-Caltech/MSSS/© T Read the entire page →
From page 209... ... 8 Question 5: Solid Body Interiors and Surfaces How do the interiors of solid bodies evolve, and how is this evolution recorded in a body's physical and chemical properties? How are solid surfaces shaped by subsurface, surface, and external processes? Read the entire page →
From page 210... ... 210 ORIGINS, WORLDS, AND LIFE Q5.1a How Much Variability in Composition and Internal Structure Is There Within and Between Solid Bodies, and How Did Such Variability Arise and Evolve? Many factors influence the initial structure of silicate bodies, including the interior oxidation state. Read the entire page →
From page 211... ... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 211 FIGURE 8-1 "Core" mass fraction for rocky (terrestrial) and icy bodies. Read the entire page →
From page 212... ... 212 ORIGINS, WORLDS, AND LIFE Q5.1b What Kinds of Internal Liquid Layers (e.g., Oceans) or Discrete Regions Occur in Solid Bodies, What Are Their Characteristics, Where Are They, and How Long Do They Persist? Read the entire page →
From page 213... ... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 213 of impurities present; thus, the temperature and ice content of the crust of icy bodies will control its mechanical properties. Particularly on small icy or rocky worlds, the low conductivity of the porous near-surface material will keep the interior warm, although high temperatures will close pores by viscous flow. Read the entire page →
From page 214... ... 214 ORIGINS, WORLDS, AND LIFE FIGURE 8-2 Internal evolution of selected solid surface bodies in the inner solar system. The conversion from geologic period boundaries to absolute ages uses commonly accepted values based on the estimated frequency of meteoroid impacts but is somewhat uncertain. Read the entire page →
From page 215... ... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 215 FIGURE 8-3 Diagram showing three different modes of planetary heat transfer, with various bodies as examples. As planets cool, melt production decreases and a heat-pipe planet may transition to plate tectonics or stagnant-lid heat transfer. Read the entire page →
From page 216... ... 216 ORIGINS, WORLDS, AND LIFE Q5.2b What Processes Control the Production and Evolution of Magnetic Fields? Within solid planetary bodies, dynamo-generated magnetic fields are typically produced by motion of conductive fluid within a metallic core. Read the entire page →
From page 217... ... QUESTION 5: SOLID BODY INTERIORS AND SURFACES 217 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 to reconstruct internal evolution and ongoing differentiation. For example, remote sensing data, in situ measurements of rocks by Mars rovers and analysis of martian meteorites record changes in composition that have been attributed to progressive cooling of the martian mantle (e.g., Baratoux et al. Read the entire page →
From page 218... ... 218 ORIGINS, WORLDS, AND LIFE Q5.3a What Internal Processes Control Surface Topography and Produce Tectonic Features? Surface topography is supported through a combination of dynamic, active processes (such as a plume of hot rising mantle material pushing up on the lithosphere, creating a topographic rise) Read the entire page →

From page 192...

... 192 ORIGINS, WORLDS, AND LIFE One of the arguments against the LHB is that the Imbrium basin could have distributed ejecta across much of the lunar nearside, and thus be dominating the observed impact record from the Apollo samples (which are all from the lunar nearside, potentially contaminated by Imbrium)