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From page 183... ... 7 Question 4: Impacts and Dynamics How has the population of solar system bodies changed through time owing to collisions and dynamical interactions, and how to match questions in Table 3.1 has bombardment varied across the solar system? How have collisions af fected the evolution and properties of planetary bodies? Read the entire page →
From page 184... ... 184 ORIGINS, WORLDS, AND LIFE body populations both in relatively stable zones and on unstable orbits. Some of the latter found their way onto orbits where they could strike the planets and satellites (e.g., Zahnle et al. Read the entire page →
From page 185... ... QUESTION 4: IMPACTS AND DYNAMICS 185 zones hitting the Moon and terrestrial planets over a billion years later. Depending on the impact signatures left behind on various worlds, the size and nature of the initial asteroid populations can be discerned by modeling the dynamical process by which these bodies are transported out of the main asteroid belt. Read the entire page →
From page 186... ... 186 ORIGINS, WORLDS, AND LIFE For the trans-neptunian belt, the extent of collisional evolution is dependent on the nature of the primordial population, when it was dynamically dispersed by a migrating Neptune (via the giant planet instability; see Questions 2 and 3) , how it was collisionally bombarded by external populations, such as the numerous planetesimals residing in the giant planet zone, and the disruption law controlling these bodies (e.g., Morbidelli et al. Read the entire page →
From page 187... ... QUESTION 4: IMPACTS AND DYNAMICS 187 resultant family members agglomerations of ice and rock, thereby allowing near-surface ice to sublimate when exposed by impacts, YORP spin-up, or some other process. It is often challenging to identify the specific process that led to mass loss on a given asteroid. Read the entire page →
From page 188... ... 188 ORIGINS, WORLDS, AND LIFE The primary source of interplanetary dust particles (IDPs) in the inner solar system is thought to be from Jupiter-family comets that disrupt at relatively small perihelion distances (Nesvorný et al. Read the entire page →
From page 189... ... QUESTION 4: IMPACTS AND DYNAMICS 189 • Benchmark the ages of asteroid families and the nature of family-forming events by observing asteroid family members in situ, counting craters on their surfaces, and comparing their model ages to dynamical evolution models of how the family members evolve. • Determine how carbonaceous chondrite asteroids and comets disrupt as they approach the Sun by observing primitive asteroids or comets at low perihelion and tracking how they evolve. Read the entire page →
From page 190... ... 190 ORIGINS, WORLDS, AND LIFE FIGURE 7-1 (A) Qualitative illustration of the early impact record of the Moon. Read the entire page →
From page 191... ... QUESTION 4: IMPACTS AND DYNAMICS 191 main belt asteroids still warm from being heated by the decay of the aluminum isotope 26Al (Q1.2c) (Bottke et al. 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) 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 183...

... 7 Question 4: Impacts and Dynamics How has the population of solar system bodies changed through time owing to collisions and dynamical interactions, and how to match questions in Table 3.1 has bombardment varied across the solar system? How have collisions af fected the evolution and properties of planetary bodies?