Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
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6 Question 3: Origin of Earth and Inner Solar System Bodies
6 Question 3: Origin of Earth and Inner Solar System Bodies
Pages 164-191
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From page 164... ...
Our inner solar system has the four terrestrial planets, Mercury, Venus, Earth, and Mars, along with Earth's large Moon, two small moons of Mars, dwarf planet Ceres, numerous 100-km class asteroids, and a multitude of small bodies that populate the asteroid belt and the inner planet region. 1 To what extent does this structure reflect a deterministic outcome of general solar system formation processes, and how much of it is instead a consequence of stochastic events that would change in unpredictable ways if the system's formation could be rerun?
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Mars, the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-2
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From page 166... ...
If not a coincidence given the small number of inner planets, this could reflect a radial gradient in oxidation fugacity among planetesimals in the early solar system, which in turn would imply limited dynamical mixing among early planetesimal reservoirs, such that the terrestrial planets mainly formed from local materials in the protoplanetary disk. In addition, two reservoirs of planetary building blocks have been identified through the analysis of both primitive and differentiated meteorites.
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Some of this reflects difficulty in implementing a multi-disciplinary approach involving expertise in diverse fields ranging from numerical modeling to chemical behavior and characteristics of potential planetary PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-4
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From page 168... ...
. Thus, at least some of the building blocks of the terrestrial planets and giant planet cores are likely to have experienced melting and differentiation prior to their incorporation into these bodies.
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From page 169... ...
Understanding the range and extent of these evolutionary processes is important to interpreting the nature of the asteroid population and for constraining the building blocks that formed the inner planets. 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, Moon, and the less explored regions of the Moon and Mars, as well as the currently unsampled small body population.
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From page 170... ...
Other outer solar system planetesimals may have struck the growing terrestrial planets, providing a source of water-rich material (Morbidelli et al. 2015 and references therein)
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● Investigate how giant planet migration after gas nebula dissipation affected the asteroid belt and terrestrial planet accretion by observing comet-like asteroids (i.e., D- and P-type bodies) within the main asteroid belt and using their properties to constrain if and how migration led to their capture into the main belt, and through dynamical and collisional models coupled to compositional constraints.
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Uncertainty persists because the spin-slowing mechanisms depend sensitively on the nature of PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-10
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From page 175... ...
compared to the much more limited isotopic compositions observed in lunar and terrestrial samples. Mars's tungsten, neodymium, as well as strontium, isotopic compositions nominally suggest that it accreted earlier than the assembly of Earth and the Moon, although these results are sensitive to the nature of core formation, late accretion, and details of the isotopic evolution models.
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. Another possible explanation for Mercury's PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-13
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Geologic activity on all of the terrestrial planets has all but destroyed the surface evidence of these primary crusts. However, this record is preserved at the Moon, where plagioclase (the first buoyant minerals that crystallize out of a magma ocean)
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From page 179... ...
. While differentiation ages of planetesimals and asteroids have not been as well determined, the observation that basaltic samples from Vesta crystallized within a few million years of the beginning of the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-16
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can contain up to ~10 percent equivalent water in hydrated minerals and a few percent carbon and nitrogen as PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 6-19
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From page 183... ...
Importantly, hydrogen, carbon, nitrogen, and oxygen trapped in chondrites, comets, and the atmospheres of the terrestrial planets have elemental and isotopic compositions markedly different from those of the protoplanetary disk as determined from the ISM or local gaseous reservoirs such as the giant planets, precluding a direct genetic relationship between the building blocks that make up the terrestrial planets and the gaseous solar nebula (e.g., Dauphas and Morbidelli 2014)
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From page 184... ...
indicating volatile elements have been added to the terrestrial planets by this process as well. Further research is needed to constrain the characteristics and abundances of nebular gas added to planetary interiors during initial accretion.
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From page 186... ...
2016. Late veneer and late accretion to the terrestrial planets.
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