AuthorRichardson Jr., James Edward
asteroid cratering records
AdvisorMelosh, Henry J.
Greenberg, Richard J.
Committee ChairMelosh, Henry J.
Greenberg, Richard J.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractImpact-induced seismic vibrations have long been suspected of being an important surface modification process on small satellites and asteroids. In this study, I use a series of linked seismic and geomorphic models to investigate the process in detail. I begin by developing a basic theory for the propagation of seismic energy in a highly fractured asteroid, and I use this theory to model the global vibrations experienced on the surface of an asteroid following an impact. These synthetic seismograms are then applied to a model of regolith resting on a slope, and the resulting downslope motion is computed for a full range of impactor sizes. Next, this computed downslope regolith flow is used in a morphological model of impact crater degradation and erasure, showing how topographic erosion accumulates as a function of time and the number of impacts. Finally, these results are applied in a stochastic cratering model for the surface of an Eros-like body (same volume and surface area as the asteroid), with craters formed by impacts and then erased by the effects of superposing craters, ejecta coverage, and seismic shakedown. This simulation shows good agreement with the observed 433 Eros cratering record at a Main Belt exposure age of $400 \pm 200$ Myr, including the observed paucity of small craters. The lowered equilibrium numbers (loss rate = production rate) for craters less than $\sim 100$ m in diameter is a direct result of seismic erasure, which requires less than a meter of mobilized regolith to reproduce the NEAR observations.This study also points to an upper limit on asteroid size for experiencing global, surface-modifying, seismic effects from individual impacts of about 70-100 km (depending upon asteroid seismic properties). Larger asteroids will experience only local seismic effects from individual impacts.In addition to the study of global seismic effects on asteroids, a chapter is also included which details the impact ejecta plume modeling I have done for the Deep Impact mission to the comet Tempel I. This work will also have direct application to impacts on asteroids, and will be used in the future to refine the cratering history modeling performed thus far.
Degree ProgramPlanetary Sciences
Degree GrantorUniversity of Arizona
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Anatomy of an Asteroid Breakup: The Case of P/2013 R3Jewitt, David; Agarwal, Jessica; Li, Jing; Weaver, Harold; Mutchler, Max; Larson, Stephen; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2017-04-21)We present an analysis of new and published data on P/2013 R3, the first asteroid detected while disintegrating. Thirteen discrete components are measured in the interval between UT 2013 October 01 and 2014 February 13. We determine a mean, pair-wise velocity dispersion among these components of Delta nu = 0.33. +/- 0.03 ms(-1) and find that their separation times are staggered over an interval of similar to 5 months. Dust enveloping the system has, in the first observations, a cross-section of. similar to 30 km(2) but fades monotonically at a rate consistent with the action of radiation pressure sweeping. The individual components exhibit comet-like morphologies and also fade except where secondary fragmentation is accompanied by the release of additional dust. We find only upper limits to the radii of any embedded solid nuclei, typically similar to 100-200 m (geometric albedo 0.05 assumed). Combined, the components of P/2013 R3 would form a single spherical body with a. radius of less than or similar to 400 m, which is our best estimate of the size of the precursor object. The observations are consistent with rotational disruption of a weak (cohesive strength of similar to 50 to 100 N m(-2)) parent body, similar to 400 m in radius. Estimated radiation (YORP) spin-up times of this parent are. less than or similar to 1 Myr, shorter than the collisional lifetime. If present, water ice sublimating at as little as 10-3 kg s(-1) could generate a torque on the parent body rivaling the YORP torque. Under conservative assumptions about the frequency of similar disruptions, the inferred asteroid debris production rate is greater than or similar to 10(3) kg s-1, which is at least 4% of the rate needed to maintain the Zodiacal Cloud.