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From page 164... ... 164 ORIGINS, WORLDS, AND LIFE An overall goal is to find evidence for or against these dynamical set pieces through missions to small bodies and/or meteorite analysis. We need to determine precisely how the signatures of post-nebula giant planet migration are recorded in small body populations and whether the nature of the asteroid belt can tell us how many giant planets existed prior to the giant planet instability. Read the entire page →
From page 165... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 165 reflect the original feedstock of both bodies. Remarkably, the silicate Earth and Moon have nearly identical isotopic compositions for many elements (e.g., oxygen, titanium, chromium, silicon, and tungsten) Read the entire page →
From page 166... ... 166 ORIGINS, WORLDS, AND LIFE non-Earth-like, one would expect measurable differences between Earth and the Moon. Instead, Earth and the Moon are nearly isotopically indistinguishable for all nonvolatile elements (e.g., Figure 6-1) Read the entire page →
From page 167... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 167 • Seek evidence for post-giant impact equilibrium between Earth and the Moon by analyzing terrestrial and lunar samples for stable refractory element isotopic compositions. • Differentiate between giant impact concepts by developing model predictions for observable properties of the Moon and Earth and comparing them with lunar compositional and geophysical data. Read the entire page →
From page 168... ... 168 ORIGINS, WORLDS, AND LIFE Q3.4b What Was the Nature of Mars's Formation and How Did Its Small Moons Originate? Mars's small mass compared to those of Earth and Venus may be evidence that some process depleted material from its orbital region before it formed (e.g., giant planet migration; Q3.2) Read the entire page →
From page 169... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 169 idea of volatile depletion through giant impact processes for large planet-size bodies has not been adequately demonstrated, and Mercury's volatile-rich nature may not disqualify the giant impact model (Ebel and Stewart 2018) Read the entire page →
From page 170... ... 170 ORIGINS, WORLDS, AND LIFE differentiated as they formed. Decay of long-lived radionuclides and accretional heating are thought to be the dominant heat sources for larger bodies. Read the entire page →
From page 171... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 171 isotopic system has been used to obtain core formation ages from samples derived from both metal cores as well as silicate mantles and crusts. This system has revealed that iron meteorites represent pieces of planetesimal cores formed in the first 1–2 million years of the solar system history (Kruijer et al. Read the entire page →
From page 172... ... 172 ORIGINS, WORLDS, AND LIFE that provided an important heat source during early times and stages of accretion. Large bodies such as Mars seem to have completed differentiation tens of millions of years later. Read the entire page →
From page 173... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 173 projectiles and how the addition of large, differentiated projectiles affect planetary surface composition and chemistry is of great importance. Addition of cometary material with its copious amounts of ices would be substantially different from accreting a volatile element depleted body like the Moon, for example. Read the entire page →
From page 174... ... 174 ORIGINS, WORLDS, AND LIFE There is a wide range of explanations for the origin and timing of observed volatile depletions and isotopic compositions. For example, some models suggest that depletion occurred prior to the assembly of the rocky parent bodies (e.g., owing to partial condensation in the nebula) Read the entire page →
From page 175... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 175 Q3.6b How Was the Inner Solar System Populated with Volatiles and How Did Volatile Delivery Evolve with Time? Hydrogen, carbon, nitrogen, and oxygen were likely incorporated into growing planetesimals in the form of ice and organic dust after the solar system had cooled following its initial formation. Read the entire page →
From page 176... ... 176 ORIGINS, WORLDS, AND LIFE Noble gas abundance patterns of the three planets are comparable, but this is difficult to reconcile with different atmospheric escape processing otherwise suggested by isotope variations. All three planetary atmospheres show a depletion of xenon relative to lighter noble gases. Read the entire page →
From page 177... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 177 SUPPORTIVE ACTIVITIES FOR QUESTION 3 • Improve knowledge of chemical and isotopic abundances through analysis of existing samples of meteorites, including martian and lunar meteorites, and continued collection of meteorites, which affords the possibility of finding meteorite samples of the other inner planets. • Continued observations of the Venus atmosphere from ALMA and other Earth- and space-based observatories to detect species potentially indicative of volcanic processes. Read the entire page →
From page 178... ... 178 ORIGINS, WORLDS, AND LIFE Canup, R.M. Read the entire page →
From page 179... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 179 Hartmann, W.K., and D.R. Davis. Read the entire page →
From page 180... ... 180 ORIGINS, WORLDS, AND LIFE Nimmo, F., and T Kleine. Read the entire page →
From page 181... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 181 Wadhwa, M., Y Amelin, O Read the entire page →
From page 182... ... Q4 PLATE: An enhanced-color image of Haulani crater on Ceres, taken by the Dawn mission in 2017. The crater has a diameter of 34 kilometers. 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? 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 164...

... 164 ORIGINS, WORLDS, AND LIFE An overall goal is to find evidence for or against these dynamical set pieces through missions to small bodies and/or meteorite analysis. We need to determine precisely how the signatures of post-nebula giant planet migration are recorded in small body populations and whether the nature of the asteroid belt can tell us how many giant planets existed prior to the giant planet instability.