<p>Many surface and dynamical processes affect the evolution of asteroids in our solar system today. The spectral slopes of S and Q-type asteroids are altered by the weathering of their surfaces due to solar wind interactions and micrometeorite impacts, as well as any processes that work to remove that weathered material. These processes of space weathering and asteroid resurfacing compete with each other to determine the spectral slope of each asteroid, with space weathering raising the spectral slope</p> <p>and resurfacing lowering it. By considering the distribution of spectral slopes with respect to orbital location and size, we can determine which potential resurfacing processes are the most dominant. I show that the distribution of spectral slopes with respect to size is present in all populations of S and Q-type asteroids in the inner solar system, regardless of orbit. I also show that the spectral slopes of S and Q-type Near-Earth Asteroids (NEAs) decrease with decreasing perihelion, but only for perihelia q < 0.9 AU.</p> <p>By building Monte Carlo and models N-body simulations of asteroids, I test which resurfacing mechanisms are consistent with these trends in spectral slopes. I find that spin-up and failure from the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect is an important resurfacing mechanism that creates the observed weathering trends with size. I also show that resurfacing asteroids due to close encounters with the terrestrial planets cannot explain the spectral slope vs. perihelion trend at q .</p> <p>0.9 AU, but that resurfacing asteroids due to thermally induced surface degradation, by assuming a power law relationship between the resurfacing timescale and the solar distance, gives much more consistent results.</p> <p>I also explore the creation rate of asteroid pairs, which are asteroids that have very similar orbits but are not gravitationally bound. The majority of pairs are formed by YORP spin-up and fission, followed by a separation of the two members. Asteroid pairs are then disassociated over time as their orbits become less similar due to chaos, resonances, and the Yarkovsky effect. I simulate both the formation of asteroid pairs in the inner main belt via YORP and their subsequent disassociation. By comparing the distribution of orbital similarity distances from observations and from our model, I estimate that asteroids fission and create an asteroid pair every 8 − 13 YORP cycles, where a YORP cycle is twice the time it takes the YORP effect to change the spin rate of an asteroid from zero to its critical spin rate. I argue that the rate of fissioning via the YORP effect is not substantially limited by any stagnation or stochastic evolution, and that losing mass via rotational fission is much less effective than collisional disruption, even for small asteroids.</p>

Thesis (Ph. D.)--University of Hawaii at Manoa, 1983. / Microfiche. / xv, 201 leaves, bound ill. 29 cm

Thesis (M.A.)--Lehigh University, 1910. / Current name of asteroid is "691 Lehigh." Manuscript. Also available online.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 246-257).

We analyzed data from the first year of a survey for Near-Earth Objects (NEOs) that we are carrying out with the Dark Energy Camera (DECam) on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory. We implanted synthetic NEOs into the data stream to derive our nightly detection efficiency as a function of magnitude and rate of motion. Using these measured efficiencies and the solar system absolute magnitudes derived by the Minor Planet Center for the 1377. measurements of 235. unique NEOs detected, we directly derive, for the first time from a single observational data set, the NEO size distribution from 1. km down to 10 m. We find that there are 106.6 NEOs larger than 10 m. This result implies a factor of 10 fewer small NEOs than some previous results, though our derived size distribution is in good agreement with several other estimates.

Title: Distribution functions of asteroid physical properties Author: Helena Cibulková Institute: Astronomical Institute of Charles University Supervisor: Mgr. Josef Ďurech, Ph.D., Astronomical Institute of Charles Univer- sity Abstract: In this thesis, I utilize photometric data sparse in time produced by all-sky surveys and investigate physical properties of large asteroid populations. In principle, the individual approach to asteroid modeling cannot compass all objects because new asteroids are continually discovered and we do not have enough data for them. Therefore, in this work I present an essentially different, statistical approach. In a series of papers, we developed two independent methods which use a triaxial-ellipsoid approximation, and we test their applicability and limits. We prove they can be used to the photometric databases like Lowell Observatory database or Pan-STARRS. The output quantities are distributions of the spin axis directions and shape elongations for asteroid populations, and using the Kolmogorov-Smirnov test we search for differences among them. The main result of my work is that the distribution of ecliptical longitudes of spin axes is nonuniform. Moreover, this nonuniformity is more significant for asteroids with low orbital inclinations and the distribution is dependent on...

No description available.

The asteroid (16) Psyche is of scientific interest because it contains similar to 1% of the total mass of the asteroid belt and is thought to be the remnant metallic core of a protoplanet. Radar observations have indicated the significant presence of metal on the surface with a small percentage of silicates. Prior ground-based observations showed rotational variations in the near-infrared (NIR) spectra and radar albedo of this asteroid. However, no comprehensive study that combines multi-wavelength data has been conducted so far. Here we present rotationally resolved NIR spectra (0.7-2.5 mu m) of (16) Psyche obtained with the NASA Infrared Telescope Facility. These data have been combined with shape models of the asteroid for each rotation phase. Spectral band parameters extracted from the NIR spectra show that the pyroxene band center varies from similar to 0.92 to 0.94 mu m. Band center values were used to calculate the pyroxene chemistry of the asteroid, whose average value was found to be Fs(30)En(65)Wo(5). Variations in the band depth (BD) were also observed, with values ranging from 1.0% to 1.5%. Using a new laboratory spectral calibration method, we estimated an average orthopyroxene content of 6% +/- 1%. The mass-deficit region of Psyche, which exhibits the highest radar albedo, also shows the highest value for the spectral slope and the minimum BD. The spectral characteristics of Psyche suggest that its parent body did not have the typical structure expected for a differentiated body or that the sequence of events that led to its current state was more complex than previously thought.

Thèse de doctorat : Sciences mathématiques : Paris, Faculté des sciences : 1880. / Titre provenant de l'écran-titre. Notes bibliogr.

High-resolution Fourier spectra in the 0.9-2.5 μm region were measured for sixteen asteroids. These data were combined with 0.3-1.1 μm spectrophotometry and 3.0-3.5 μm narrowband photometry for compositional analysis. Comparison spectra of meteorites and terrestrial minerals were measured in the laboratory, some under simulated asteroidal conditions of pressure and temperature. Spectra of eleven representative S-type asteroids show a range of olivine/pyroxene ratios overlapping those of ordinary and carbonaceous chondrites, but not approaching those of common differentiated meteorite types. The reddening in the asteroid spectra implies the presence of metallic iron, but if the metal is finely divided its abundance could be low. S-type asteroids have spectra most consistent with undifferentiated compositions, and some of them, especially 8 Flora, could be ordinary chondrite parent bodies. 4 Vesta and 349 Dembowska are unusual asteroids which have spectra resembling those of achondritic meteorites. Vesta has a pyroxene-feldspar mineralogy intermediate in composition between eucrites and howardites. If shergottite-like basalts are present, they must be in low abundance. Dembowska has an olivine-pyroxene mineralogy similar in some ways to ordinary chondrites, but there is considerable evidence that it is actually a fragment of the mantle of a differentiated Vesta-like parent body. The most diagnostic spectral feature seen on three low-albedo asteroids is the 3 μm band due to water of hydration. 1 Ceres must consist mostly of a low-iron clay mineral with some hydrated salts. 2 Pallas has a low abundance of hydrated minerals relative to Ceres, with the bulk of its composition being anhydrous iron-free silicates. 324 Bamberga probably contains clay minerals, but its spectrum is dominated by abundant magnetite. These and other C-type asteroids have surface compositions consistent with massive aqueous alteration of primary carbonaceous chondrite minerals. These results all indicate that the compositions of main belt asteroids are more closely related to the compositions of meteorites than was previously believed. S-type and C-type asteroids are undifferentiated assemblages of which ordinary and carbonaceous chondrites are an incomplete sample. Differentiated meteorites could be derived from the other relatively rare asteroid types.