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From page 157... ... 6 Question 3: Origin of Earth and Inner Solar System Bodies How and when did the terrestrial planets, their moons, and the asteroids accrete, and what processes determined their initial properties? To what extent were outer solar system materials incorporated? Read the entire page →
From page 158... ... 158 ORIGINS, WORLDS, AND LIFE is a critical component for constraining both the physical and chemical characteristics of the terrestrial planets, as well as for understanding the processes that occurred in the protoplanetary gas nebula. However, many fundamental questions remain unanswered. Read the entire page →
From page 159... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 159 The innermost planet, Mercury, has a highly reduced surface, with low iron contents and unexpectedly high sulfur contents, consistent with a planet formed from highly reduced materials. Information about the composition of Venus is extremely limited, a fundamental gap in our understanding of the compositional variations among the terrestrial planets. Read the entire page →
From page 160... ... 160 ORIGINS, WORLDS, AND LIFE obtained or recognized if they exist within our meteorite collection. Refined in situ geochemical characterization of surface materials at Mercury and Venus would transform our knowledge of these bodies, especially in the absence of samples. Read the entire page →
From page 161... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 161 treating many stages of evolution and planetary size scales simultaneously in numerical models, which may be needed to ultimately link large-scale planet accretion to the meteoritic record and small body populations. We also may not fully understand the dynamic interplay between nebular gas, dust, nascent planetesimals, and the Sun. Read the entire page →
From page 162... ... 162 ORIGINS, WORLDS, AND LIFE Strategic Research for Q3.1 • Determine the compositional diversity of the terrestrial planets and inner solar system feedstocks by obtaining mineralogical, geochemical, and isotopic data from the surfaces and atmospheres of Mercury, Venus, the Moon, and the less explored regions of the Moon and Mars, as well as the currently unsampled small body population. • Determine the diversity of compositions and nature of remnant planetesimals residing in the inner solar system and establish links between the small body taxonomy and meteorite types through Earth based and spacecraft-based remote sensing, in situ measurements, and laboratory analyses of meteorites and returned samples. Read the entire page →
From page 163... ... QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 163 in distinct chemical reservoirs (Q1.3) 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. 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 157...

... 6 Question 3: Origin of Earth and Inner Solar System Bodies How and when did the terrestrial planets, their moons, and the asteroids accrete, and what processes determined their initial properties? To what extent were outer solar system materials incorporated?