In order to search for evidence of hydration on M-type asteroid (16) Psyche, we observed this object in the 3 mu m spectral region using the long-wavelength cross-dispersed (LXD: 1.9-4.2 mu m) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope Facility. Our observations show that Psyche exhibits a 3 mu m absorption feature, attributed to water or hydroxyl. The 3 m absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to OH- and/or H2O-bearing phases (phyllosilicates). The detection of a 3 mu m hydration absorption band on Psyche suggests that this asteroid may not be a. metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 Gyr. Our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of Psyche.

No description available.

The inner main asteroid belt is an important source of near-Earth objects and terrestrial planet impactors; however, the dynamics and history of this region are challenging to understand, due to its high population density and the presence of multiple orbital resonances. This dissertation explores the properties of two of the most populous inner main belt family groups - the Flora family and the Nysa-Polana complex - investigating their memberships, ages, spin properties, collision dynamics, and range in orbital and reflectance parameters. Though diffuse, the family associated with asteroid (8) Flora dominates the inner main belt in terms of the extent of its members in orbital parameter space, resulting in its significant overlap with multiple neighboring families. This dissertation introduces a new method for membership determination (the core sample method) which enables the distinction of the Flora family from the background, permitting its further analysis. The Flora family is shown to have a signature in plots of semimajor axis vs. size consistent with that expected for a collisional family dispersed as a result of the Yarkovsky radiation effect. The family's age is determined from the Yarkovsky dispersion to be 950 My. Furthermore, a survey of the spin sense of 21 Flora-region asteroids, accomplished via a time-efficient modification of the epoch method for spin sense determination, confirms the single-collision Yarkovsky-dispersed model for the family's origin. The neighboring Nysa-Polana complex is the likely source region for many of the carbonaceous near-Earth asteroids, several of which are important targets for spacecraft reconnaissance and sample return missions. Family identification in the Nysa-Polana complex via the core sample method reveals two families associated with asteroid (135) Hertha, both with distinct age and reflectance properties. The larger of these two families demonstrates a correlation in semimajor axis and eccentricity indicating that its family-forming collision occurred near the parent body's aphelion. In addition, the Eulalia family is connected with a possible second component, suggesting an anisotropic distribution of ejecta from its collision event.

Thèse--Faculté des sciences de Paris, 1877.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographic references (leaves [106]-109).

Thesis (Ph. D.)--University of Chicago, 1915. / "A Private edition distributed by the University of Chicago Libraries." Reprinted from the Astronomical journal, v. 29, nos. 11-12. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, 1915. / "A Private edition distributed by the University of Chicago Libraries." Reprinted from the Astronomical journal, v. 29, nos. 11-12. Includes bibliographical references. Also available on the Internet.

Dwarf planet Ceres (empty set similar to 940 km) is the largest object in the main asteroid belt. Investigations suggest that Ceres is a thermally evolved, volatile-rich body with potential geological activity, a body that was never completely molten, but one that possibly partially differentiated into a rocky core and an ice-rich mantle, and may contain remnant internal liquid water. Thermal alteration and the infall of exogenic material contribute to producing a (dark) carbonaceous chondritic-like surface containing ammoniated phyllosilicates. Here we report imaging and spectroscopic analyses of data on the bright Oxo crater derived from the Framing Camera and the Visible and Infrared Spectrometer on board the Dawn spacecraft. We confirm that the transitional complex crater Oxo (empty set similar to 9 km) exhibits exposed surface water-ice. We show that this water-ice-rich material is associated exclusively with two lobate deposits at pole-facing scarps, deposits that also contain carbonates and admixed phyllosilicates. Due to Oxo's location at -4802 m below the cerean reference ellipsoid and its very young age of only 190 ka (1 sigma: +100 ka, -70 ka), Oxo is predestined for ongoing water-ice sublimation.

Understanding asteroid collisions is a key part of Solar System science. To in- terpret observations of more than 100 asteroid families, various numerical sim- ulations are used. In this work, we prefer the smoothed particle hydrodynamics (SPH), which allows a detailed description of impact mechanics, shock wave propagation, fragmentation of the target, ejection, or reaccumulation controlled by self-gravity and secondary collisions. Since the respective time scale may reach the orbital time scale, the SPH is often complemented by efficient N-body integrators and collisional handlers. In the review part of the thesis, we describe details of numerical methods and their implementation in the new OpenSPH code. We also thoroughly test the code, using analytical solutions and labora- tory experiments as references, and discuss its stability and convergence with respect to spatial resolution. In the refereed papers, included in the thesis, we focus on collisions with targets of particular sizes (D = 10 and 100 km). We explore the dependence of outcomes on the target size, the projectile size, the impact speed, the impact angle, and most importantly, the initial spin rate. We demonstrate that rotation significantly decreases the effective strength of the targets and increases the ejected mass. We self-consistently...

In the last few years, two major contributions to the asteroid database have been the eight-color and thermal radiometric surveys. The former consists of broad-band photometric measurements through eight filters spanning the 0.3 to 1.1 μm wavelength range. The latter consists of thermal flux measurements at 10 and/or 20 μm, and when combined with measures of the reflected light, can yield reliable estimates of their geometric albedos. Visual display of the eight-color survey data can be simplified by reducing the dimensionality of the problem. A principal components analysis was performed to accomplish this task. The analysis shows that 95 percent of the information contained in the seven independent color indices is contained in two principal components. This result is due to the fact that most asteroid spectra can be explained in terms of two absorption features, one at ultraviolet and the other at near-infrared wavelengths. The photometric and radiometric data sets were also used, along with cluster analysis techniques, to produce an improved asteroid taxonomic system. Seven major classes are now recognized and are designated A, C, D, E, M, P, and S. Three interesting minor classes are also identified: B, F, and G. Marginal evidence for an eighth major class, here called T, exists in the data, but the reality of this class awaits confirmation by further observations of potential members. Three asteroids do not fall into any of the above classes and are assigned unique designations: R (349 Dembowska), Q (1862 Apollo), and V (4 Vesta). Four E-class asteroids are now known to exist in the main belt, yet nearly twice this number exist in or near the Hungaria region. Twenty eight D-class asteroids have been identified in the outer belt, where they represent a significant fraction of the population. Five D asteroids exist in the main belt, which one lying near the inner edge of the belt, which is dominated by S-class asteroids. Two of the interesting minor classes are associated with particular dynamical families. The Nysa family, with the single exception of Nysa itself, consists entirely of class F asteroids, while the B asteroids are found almost exclusively in the Themis family. The earth-approaching population is represented by at least two objects similar to Vesta and Dembowska, which are as many as are in the entire main belt, while most of the earth-approachers are of class S.