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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LINK ANALYSIS FOR THE NEAR EARTH ASTEROID PROSPECTORBarton, Randal L.; New Mexico State University (International Foundation for Telemetering, 1998-10)The Near Earth Asteroid Prospector (NEAP) has a scheduled launch date between mid- 1999 and mid-2000, and will encounter a yet to be determined near Earth asteroid (1.1 - 2.2 AU distance from Earth) some ten months later . The purpose of this mission is not only to collect valuable scientific and geological data, but to also determine the value of the asteroid’s materials for possible mining and exploitation , . The purpose of this paper is to detail frequency allocation issues and to determine possible return (space to Earth) data rates associated with deep space communications with the NEAP spacecraft.
HUBBLE SPACE TELESCOPE OBSERVATIONS OF ACTIVE ASTEROID 324P/La SAGRAJewitt, David; Agarwal, Jessica; Weaver, Harold; Mutchler, Max; Li, Jing; Larson, Stephen; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2016-09-06)Hubble Space Telescope observations of active asteroid 324P/La Sagra near perihelion show continued mass loss consistent with the sublimation of near-surface ice. Isophotes of the coma measured from a vantage point below the orbital plane are best matched by steady emission of particles having a nominal size. of. a similar to 100 mu m. The inferred rate of mass loss, dM(d)/dt similar to 0.2 kg s(-1), can be supplied by sublimation of water ice in thermal equilibrium with sunlight from an area as small as 930 m(2), corresponding to about 0.2% of the nucleus surface. Observations taken from a vantage point only 0.degrees 6. from the orbital plane of 324P set a limit to the velocity of ejection of dust in the direction perpendicular to the plane, V-perpendicular to < 1 m s(-1). Short-term photometric variations of the near-nucleus region, if related to rotation of the underlying nucleus, rule-out periods <= 3.8 hr and suggest that rotation probably does not play a central role in driving the observed mass loss. We estimate that, in the previous orbit, 324P lost about 4 x 10(7) kg in dust particles, corresponding to 6 x 10(-5) of the mass of a 550 m spherical nucleus of assumed density rho = 1000 kg m(-3). If continued, mass loss at this rate would limit the lifetime of 324P to similar to 1.6 x 10(4) orbits (about 10(5) years). To survive for the 100-400 Myr timescales corresponding to dynamical and collisional stability requires a duty cycle of 2 x 10(-4) <= f(d) <= 8 x 10(-4). Unless its time in orbit is overestimated by many orders of magnitude, 324P is revealed as a briefly active member of a vast population of otherwise dormant ice-containing asteroids.
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