Io's mountains are cataloged in order to investigate their formation. Of the 101 mountains imaged with sufficient coverage and resolution for further analysis, 4 are volcanoes, and 97 are tectonic massifs. Of the 97 tectonic mountains, ≥40 abut paterae (volcanic or volcano-tectonic depressions). This juxtaposition is unlikely to be coincidental as the probability of it occurring by chance is ∼1.08%. The observed mountain-patera association may be due to orogenic faults acting as conduits for magma ascent, thus fueling patera formation near mountains. As resurfacing buries a shell of material from Io's surface to the base of the lithosphere, its effective radius is reduced and it heats up. The volume change due to subsidence and thermal expansion is calculated as a function of lithospheric thickness. Conservation of volume dictates that this material is uplifted at Io's surface. By estimating the total volume of mountains, Io's average lithospheric thickness is constrained to ≥12 km. A kinematic analysis of Nefertiti Corona, Venus, reveals that the corona's interior moved east as a relatively coherent thrust sheet with most deformation occurring on the distal margin. Additionally, an en-echelon array indicates a history of semi-brittle deformation on the northern side of Nefertiti's tectonic annulus. Regional heating from the thermal diapir that formed Nefertiti probably reduced the crustal viscosity and enabled the semi-brittle deformation. The "Odessa Craters" in the Channeled Scabland of eastern Washington State are basaltic ring structures (BRSs) 50-500 m in diameter that are comprised of discontinuous, concentric outcrops of subvertically-jointed basalt and autointrusive basaltic dikes. It is postulated that they formed as follows: phreatovolcanic activity disrupted a relatively thin, active lava flow forming rootless cones; the lava flow inflated around the cones; tensile stresses caused concentric fracturing; dikes exploited the fractures and fed lava to the surface; and subsequent erosive floods excavated the structures. A second population of BRSs near Tokio Station, WA, are morphologically analogous to quasi-circular structures in Athabasca Valles, Mars (a region that is geologically similar to the Channeled Scabland). If the martian features formed as BRSs, then they indicate local water-lava interactions and at least two floods through Athabasca Valles.

We present a study of a sample of starburst galaxies. The systems chosen for study range in age and strength. We have obtained high-quality infrared spectroscopy and imaging of 18 starburst galaxies and 4 early-type galaxies as a comparison sample of an old stellar population. The spectra consist of high-resolution data (R ∼ 3000) in the H (1.65μm) and K (2.2μm) bands and, in a few cases, the J (1.25μm) band; most of the J-band spectra were obtained at a resolution of 800. We obtained broadband images of all the galaxies in the J, H, and K bands, as well as narrowband images of several of the galaxies in the (1.0)S(1) line of H₂ and in Brγ. We use these data and data from the literature to constrain models of the nuclear starbursts for these galaxies. The high sensitivity and resolution of the spectra plus the use of a long slit allows us to derive kinematic properties of the nuclear region in addition to other constraints on the starburst population, such as ionizing flux and CO index. We compare the properties of these galaxies and suggest that a burst of star formation can account for the galaxy properties and that the range of properties observed is derived from a range of burst ages and strengths. Our high-quality data allow us to examine the properties of the (Fe II) and H₂ emission regions. We measure, for the first time, the density in the (Fe II) -emitting region of a starburst galaxy and find that this density is consistent with the origin of this emission in supernova remnants. We find, in contrast to earlier studies, that fluorescence plays a large role in the H₂ emission of some starburst galaxies.

A new λ = 1.3 mm polarimeter, Cyclops, was constructed to make observations of dust continuum emission from star formation regions. The polarization of the inner arcminute of DR 21 was mapped with Cyclops. The polarization percentage and position angle are remarkably constant, indicating a uniform magnetic field throughout the cloud. Turbulent gas motions are a more significant source of support against self gravity in the cloud core than thermal pressure or magnetic fields. The polarization toward the cloud core increases slightly from λ = 100 μm to λ = 2 mm and is consistent with the standard dust composition of silicates and graphite. A small continuum polarization survey of cloud cores with embedded protostars was made with Cyclops and combined with observations from the literature. There is no clear tendency for any preferred alignment of cloud core elongations with respect to magnetic field lines, especially for the bright, high mass star forming regions. This confirms that the massive cloud cores are magnetically supercritical. The magnetic field lines appear randomly oriented with respect to the local Galactic plane position angles, implying that the random component of the Galactic magnetic field dominates the spiral component in this sample. Three-σ upper limits of 0.4%, 1.2%, and 1.2% were placed on the polarization of the HCO⁺ J = 1-0 emission line from the DR 21 and Mon R2 molecular outflows, and the CS J = 2-1 line from the IRAS 16293-2422 molecular outflow, respectively. These polarizations are an order of magnitude lower than predicted by theoretical models. In the case of DR 21, the lack of polarization is probably due to a disordered magnetic field in clumpy, turbulent gas, although multiple scattering may also diminish the polarization. CS J = 2-1 polarizations of 0.9% ± 0.1% and 5.1% ± 1.5% were observed from the envelopes of the evolved stars IRC+10216 and CRL 2688, respectively. An anisotropic optical depth to escape of infrared photons from the central star, perhaps caused by a toroidal dust distribution, could generate the IRC+10216 polarization.

The relationship between the radio and optical properties of quasars and the connection between these properties and the quasar host galaxies are investigated. Radio data have been analyzed for 359 of the 1055 quasars in the Large Bright Quasar Survey (LBQS). A major result of this work is that the radio-loud fraction is mostly insensitive to redshift and quasar optical luminosity, remaining at ≈ 10% over the absolute magnitude range -28 ≤ M(B) ≤ -23 and from redshifts z = 0.2 to z ∼ 5. Two deviations from these flat distributions occur at z ∼ 1, where there is a modest increase in the radio-loud fraction, and for absolute magnitudes brighter than M(B) = -28, where the fraction climbs to 20-30%. The rise in radio-loud fraction at z ∼ 1 is reproduced by a model based on the optical and radio quasar luminosity functions. The increase at high optical luminosities is consistent with the existence of two radio emission mechanisms, one correlated with optical luminosity, the other independent. The nearly flat distributions in the LBQS differ markedly from those of the optically selected Palomar-Green Bright Quasar Survey and the X-ray selected Extended Medium Sensitivity Survey. A subset of 16 LBQS quasars was imaged with the Hubble Space Telescope to study the dependence of radio and optical luminosity on the absolute magnitudes and morphologies of the host galaxies. There is no distinction in host galaxy magnitude between radio-loud and radio-quiet quasars, assuming they are all of the same galaxy type. The magnitudes of the hosts are ≳ L*, and the optical luminosities of the hosts and nuclear components are positively correlated. Many of the host galaxies have small axial ratios, which may indicate that they are inclined disk systems; or else they have bright elongated features which are visible while the bulk of the underlying lower surface brightness components of the host galaxy are not.

A geologic study of lithospheric displacements on the Jovian moon Europa reveals lateral motions and plate flexure. Tectonics are governed by the rotation rate, nature of the lithosphere and underlying decoupling layer, the nature and causes of lateral displacements, plus mechanisms for creating and consuming surface area, and for restoring lithospheric rigidity. Astypalaea Linea is an 810-km-long strike-slip fault near the south pole, with 42 km of right-lateral offset, and includes a large pull-apart. Considering scale and contaminants, the lithosphere may have a tensile strength of ∼2.5 bars. The fault probably formed as a crack due to stresses from nonsynchronous rotation and diurnal tides, and was displaced by "walking" due to diurnal tides. Adjacent regional structures record earlier episodes of strike-slip. Wedge-shaped bands in the antijovian fracture zone are reconstructed, confirming the occurrence of block rotation and episodic dilation. A band on the leading side of the satellite is also reconstructed. Whether these bands formed under the influence of the same stress patterns which caused Astypalaea Linea is unclear; regional structures in the antijovian region suggest deformation by distributed shear. Dilation has also occurred across at least one ridge representative of a type independently interpreted as dilational based on ridge morphology. Other ridges apparently flex the underlying lithospheric plate downward. The lithosphere is inferred from flexural parameters at one locality to be 0.25-3.5 km thick. New lithosphere forms by ratchet-type spreading at bands and some ridges. Surface area may be removed by chaos formation or other processes. A global time marker based on a shift in ridge size is used to show that displacement was probably long-lived as well as widespread. During displacement, lithospheric plates were rigid and integral despite the appearance of cracks, perhaps due to annealing processes. Tides are the primary driving force for Europan tectonics and have produced a complex geologic history, consistent with Greenberg et al. (1997). A subsurface ocean, maintained by tidal heating, probably existed at the time of the displacements, which are relatively recent, and may well exist today.

We present detailed studies of the kinematics and star formation properties of low surface brightness (LSB) galaxies. A total of five giant LSB galaxies including the prototype, Malin 1, were imaged in the 21-cm line of H sc I to provide the first glimpse into the kinematics of these systems. We find that these are some of the first examples to be uncovered of galaxies that are both massive and dark matter dominated. We also find that most of the galaxies have gas surface densities that lie below the critical density for star formation at all radii, consistent with their lack of star formation. In a couple of cases, though, the gas exceeds the critical density where there is no star formation implying a higher gas velocity dispersion or strong flaring of the gas disk. Long-slit optical spectroscopy and broadband CCD imaging are presented for a total of 71 LSB galaxies. We find that these galaxies follow a Fisher-Tully relation with a slope that is in good agreement with the slopes found for other samples of LSB and HSB galaxies. We interpret both the optical and H sc I rotation curves in terms of mass models consisting of a halo only or a stellar component plus a halo of either an isothermal form or an NFW halo of the form described by Navarro et al. (1996) and find that the rotation curves are generally best modeled by low mass-to-light ratio stellar components. By modeling the rotation curves with only an NFW halo and comparing the results with the predictions of cosmological simulations we find that these data are marginally consistent at best with Standard Cold Dark Matter and generally favor lower density models. However, we also find that when including the stellar component, the NFW halo gives a significantly worse fit than an isothermal halo in many cases. This suggests that the inner parts of galactic halos may not be well described by the NFW halo profile.

Tides due to orbital eccentricity may have a substantial effect on the rotation and tectonics observed on Jupiter's moon, Europa. A direct measurement of Europa's rotation rate has been made by measuring the positions of surface features relative to the terminator in both Voyager and Galileo images. From these measurements I have found that the rotation of Europa relative to the direction of Jupiter is <0.5° over a 17 year period, i.e. one rotation with respect to Jupiter would require at least 12,000 years. Non-synchronous rotation is also a significant source of global stress which, combined with the diurnal tidal stress, provides a failure mechanism resulting in tensile cracks on a global scale. The stress associated with rotational and diurnal tides can also explain the orientations and age relationships observed regionally in Europa's northern hemisphere. Additional global scale linear features also strongly correlate to these stress fields suggesting that they too may have also formed as cracks. After crack formation, diurnal tides may significantly affect the evolution of cracks through either ridges formation, regional extension, or strike-slip motion. The process of tidal shear displacement is analagous to actual walking. Mapping of five different regions on Europa has revealed 121 strike-slip faults. Based on these observations, Europa appears to support the formation of right-lateral faults in the southern hemisphere and left-lateral faults in the northern hemisphere. The theory of tidal walking predicts exactly that dichotomy on average over the hemispheres. Additionally, all of the mapped strike-slip faults were associated with double ridges and bands, but none were detected along cracks. Thus, cracks (even older ones) without ridges apparently have not generally penetrated to a decoupling layer, consistent with models for ridge formation that require cracks to penetrate to a liquid water ocean.

We study thermally induced density perturbations during inflation. This scenario is characterized by two thermodynamic conditions: (i) the primordial perturbations originate in the epoch when the inflationary universe contains a thermalized heat bath; (ii) the perturbations of the inflationary scalar field are given by the fluctuation-dissipation relation. We show that (1) the power spectrum of the primordial density perturbations follows a tilted power law behavior; (2) the relation between the amplitude and the power index of the spectrum exhibits a "thermodynamic" feature--it depends mainly on the thermodynamic variable M, the inflation energy scale; (3) both the adiabatic mode and the isocurvature mode of density perturbations appear during the inflation epoch, and the resultant power spectrum on super-horizon scales is substantially suppressed. These results are found to be very consistent with observations of the temperature fluctuations in the cosmic microwave background if the energy scale of the inflation is about 10¹⁵-10¹⁶ GeV.

I have used the SALE2D hydrocode to study spall in impacts into layered terrains. Application of my results to the problem of martian meteorite provenance resolves two outstanding paradoxes. First, the minimum size crater previously thought to be required to eject martian meteorites is so large (12 km) that it is highly unlikely such an event occurred on shergottite age terrain in the last few million years. The geochemical evidence supports four launch events. This issue I have resolved by establishing a new lower limit to the minimum size crater of 3 km. Second, the martian meteorites are dominated by shergottites (62%) which come from the youngest and apparently rarest martian terrains. The vast majority of Mars appears to be under represented. This paradox lies on the false premise that all terrains are equally efficient in launching material during an impact. I have found that the presence of a weak, low density layer suppresses spall velocity and increases shock pressures in an impact. Since the regolith on Mars can be expected to be largely impact-generated, the older terrains are covered by a greater depth of regolith. Qualitatively, older terrains are under represented in the martian meteorites because they require larger (rarer) impacts to launch material into space. I have shown this quantitatively for shergottites, nakhlites, and Chassigny. An extension of my work provides some constraints on the extent of martian ancient terrain.

The solar system began with the collapse of a dense molecular cloud, which is rich in atoms, dust grains and diverse molecules. The complexity of different physical and chemical processes which happened during the formation of the early solar system constitute a major topic within our scientific community, even though a complete model of the solar nebula including all such processes has not been constructed. This thesis deals with some of these chemical and physical processes and consists of two phases. In the first phase of my work, I have studied the heating of water-ice grains during infall into the solar nebula from the surrounding collapsing cloud. The investigations in this phase extend previous studies (Lunine et al., 1991) in two aspects. Firstly, we revise the previous grain heating model. The calculations for large fluffy grains (up to 10μm) are conducted. Secondly, we explicitly incorporate terms associated with various exothermic and endothermic reactions which contribute to the thermal evolution of the grains in our computation. By tracking the threshold temperatures reached as a function of grain size, density and infall velocity, we are able to quantify the evolution of infalling interstellar grains. Once the volatiles were brought in by the ice grains, codeposition of diversed volatiles on the surface of refractory grains happened in the cold solar nebula region. Disk dynamical evolution leads to a background temperature below 50K at distance beyond 20AU. Studies have shown that amorphous water ice forms at this temperature range. Amorphous ice can volumetrically absorbs a large amount of volatiles. My work in the second phase consists of investigations of amorphous water ice, especially its property of trapping various volatiles under conditions well outside the stability field of the condensed phases of the volatiles. A statistical thermodynamical model has been established. It is used to predict fractional abundances of trapped volatiles in different temperature and pressure conditions. Our investigations involve both theoretical and experimental studies.