Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
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7 Question 4: Impacts and Dynamics
7 Question 4: Impacts and Dynamics
Pages 192-218
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From page 192... ...
Q4.1 HOW HAVE PLANETARY BODIES COLLISIONALLY AND DYNAMICALLY EVOLVED THROUGHOUT SOLAR SYSTEM HISTORY? The major set pieces of early solar system evolution, namely planet formation and giant planet migration, depleted early small body reservoirs, created new ones, and reconfigured most through mutual collisions between planetesimals (e.g., see Questions 2 and 3; Nesvorný 2018 and references therein)
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From page 193... ...
. These former Kuiper belt planetesimals produced most early impacts on outer solar system worlds, and they were a strong component in the initial bombardment of terrestrial planets and asteroid belt as well.
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From page 194... ...
The events involved with planet formation and giant planet migration (see Questions 2 and 3) left the solar system with two primary small body reservoirs within our observational reach: the asteroid and transNeptunian belts, and several smaller ones, such as those populations captured in mean motion resonance with giant planets (e.g., Trojan asteroids of Jupiter and Neptune, the Hilda asteroids)
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From page 195... ...
2021) , there are PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-4
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From page 198... ...
Despite the usefulness of crater records, there are many potential sources of error -- including observational errors and errors caused by geologic disruptions -- that need to be better understood if impact crater populations are to be used for reliable age determinations. Most critically, the contribution of secondary craters and sesquinary craters, together with the processes that degrade, relax, or remove craters, PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-7
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From page 199... ...
Their relative importance depends on how the impact flux from those populations changed with time as well as the context of the worlds in question, namely when did they form and what happened to them when they were struck. Starting with comets, their impacts dominate the bombardment of outer solar system worlds, with the magnitude of the early flux dependent on the timing of giant planet migration and the size of the primordial Kuiper belt (see Question 2)
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From page 200... ...
If the LHB was a real uptick in the impact flux hundreds of millions of years after the end of planet formation, the late timing needs an explanation, because this is not expected from the declining remnants PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-9
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From page 202... ...
A requirement for 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.
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From page 203... ...
Eventually, these collisional cascades will deliver bodies to a main belt escape route, such as a powerful resonance with the giant planets, where they can be driven onto orbits from where they can strike the terrestrial planets. This process keeps the planet-crossing asteroid population fairly steady over time, and it helps explain why the main belt, planet-crossing asteroids, and terrestrial crater populations have similar size frequency distributions (e.g., Bottke et al.
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From page 204... ...
For example, as discussed below, comets striking giant planet satellites often produce enormous ejecta showers, which in turn produce numerous secondary and sesquinary craters. The contribution of these types of craters to small crater populations on a wide range of terrains is uncertain, partly because impact events produce variable ejecta size distributions but also because our understanding of small comet populations is limited.
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From page 205... ...
In the case of the Moon, this event would have provided enough energy to melt a large portion and form a deep PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-14
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From page 211... ...
● 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 Q4.4 HOW DO THE PHYSICS AND MECHANICS OF IMPACTS PRODUCE DISRUPTION OF AND CRATERING ON PLANETARY BODIES? Impact events have been ubiquitous across the solar system.
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From page 212... ...
The redeposition and orbital distribution of fragments and ejecta becomes more complex as a body's size decreases, with an increasing portion of an ejecta field escaping or entering into a long-lived orbit. For some impacts, ejecta can become distributed globally across the body and can cause measurable PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-21
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From page 213... ...
● 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) by performing high resolution imaging of impact crater morphology on various outer solar system bodies ● Determine how impacts crush porous structures and materials on comets and asteroids in microgravity by characterizing the density variations beneath impact craters based on impact experiments, high-resolution gravity measurements, and remote sensing observations SUPPORTIVE ACTIVITIES FOR QUESTION 4 ● Establish a well constrained chronology for events in the solar system through improved cataloging of impactor reservoirs using ground- and space-based assets, improved dynamical simulations of the formation and evolution of small bodies, improved mapping of new craters on all planetary surfaces, more complete observations of present-day small body impacts in different contexts, remote dating of planetary surfaces, dating of samples via in situ methods and/or returned samples from diverse bodies, and improved modeling of crater formation.
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